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#41
Posted to rec.audio.tubes
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Explanation still required for triode superiority
On Tue, 26 Sep 2006 10:01:18 +0100, Eeyore
wrote: It's a subject that truly intruiges me. Where I suspect I'd differ with you is that I'd expect a DSP simulation to sound just the same as the beloved triode. It is something that I'm looking into btw. Could we begin by agreeing that a simulation is at least *possible*, including *all* possible issues, including non-linearities in time and amplitude, and at all levels; and will happen, for reproduction (not real time) soon. Slightly, a few orders of magnitude, no biggie, of horsepower will extend this to close-enough-to-real time for performance. Again, soon... ish. The first step to that goal is right here, right now, to define the actual things that need to be captured. There are *real* things to be captured, not fantasies. And I'd suggest that it's a worthwhile and potentially interesting target. Much thanks, as always, Chris Hornbeck |
#42
Posted to rec.audio.tubes
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Explanation still required for triode superiority
On Wed, 27 Sep 2006 02:44:56 GMT, Chris Hornbeck
wrote: Could we begin by agreeing that a simulation is at least *possible*, including *all* possible issues, including non-linearities in time and amplitude, and at all levels; Should add that I don't actually know if this can be done. Randy Yates seemed to feel quite differently about a related issue, and I don't have the mental horsepower to dispute his opinion. But, maybe as a talking point... Much thanks, Chris Hornbeck |
#43
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Chris Hornbeck wrote: On Tue, 26 Sep 2006 10:01:18 +0100, Eeyore wrote: It's a subject that truly intruiges me. Where I suspect I'd differ with you is that I'd expect a DSP simulation to sound just the same as the beloved triode. It is something that I'm looking into btw. Could we begin by agreeing that a simulation is at least *possible*, Very much so I think. including *all* possible issues, including non-linearities in time and amplitude, and at all levels; I don't see where time comes into it actually. Do feel free to comment on this point. and will happen, for reproduction (not real time) soon. What do you mean by not real time ? I'm entirely sure it's possible to simulate in real time. Modern inexpensive DSPs offer ~ 100MIPS. Using say 96kHz sampling that allows ~ 1000 instructions per sample period which I'm sure will suffice. Slightly, a few orders of magnitude, no biggie, of horsepower will extend this to close-enough-to-real time for performance. Again, soon... ish. The first step to that goal is right here, right now, to define the actual things that need to be captured. Yes, I'd agree there. I'm still considering the best way to approach the 'modelling' required. There's a few ways of doing it. There are *real* things to be captured, not fantasies. And I'd suggest that it's a worthwhile and potentially interesting target. It certainly has my interest. Graham |
#44
Posted to rec.audio.tubes
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Explanation still required for triode superiority
On 26 Sep 2006 15:30:25 -0700, "Andre Jute" wrote:
3. We make totally unwarranted assumptions of monotonicity. This is a fatal flaw in our thinking, and we all do it, all the time. 4. We make often unwarranted assumptions about input signal bandwidth. 5. We *always* *without exception* forget to properly weight the importance of simply being upstream in the signal path. Always. elaborate on points 3, 4 and 5. We're always fighting the last war. In my on-war-footing and yet war-unravaged country, this seems particularly unwise, but still unavoidable. Progress in any sufficiently mature technology is less a matter of perfecting the existing technology than in identifying the flaws in the model by which the technology was created. Any second rate modern military power could have ruled the world of even only a hundred years ago. And, conversely, the Number One Military Might Big Kahuna in the contemporary world can't defeat a determined insurgency in a militarily defeated and occupied country. (Or two). Defining the problem is everything. Defining the problem in the context of the last war is foolish, but seemingly unavoidable. Failure to recognize this trap is potentially fatal militarily, and a blind alley technically. Which conclusion? That "triodes sound better" or that "there must be an electrical explanation"? strong disagreement ('cause that ain't science!) with the latter. Eh? Surely a thermionic valve is nothing but a bunch of electrical impulses created by vacuum, wire and electricity? Whatever happens in there, regardless of whether we can see it or not, regardless of what we call the result, *must* perforce have an *electrical* explanation. °That* is science. Anything else would make me uncomfortable -- and me a certified witchdoctor! Gotta be more careful with my phraseology. It really depends on what "be" be. Arf! Have I heard a technically compelling explanation for ..some.. of the things that I nonetheless believe to be both true and ultimately explainable to me in terms that I can accept as real? No. Do I believe that explanations acceptable to me exist and are awaiting discovery? Yes. Science is the quest(ion) itself, so we really aren't in disagreement. And, I'll try to work up some more keystrokes about my favorite bete noirs, monotonicity and operating level later, 'gator. Much thanks, as always, Chris Hornbeck |
#45
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Somebody said, and Andre replied..... Modeling and analysis are essential; but the map is not the world. Actually, the only °essential* is having some method of deciding where you want to arrive. High fidelity went wrong long before Mr Leak's inspired marketing terminology (Point One) became an engineering article of faith, but that set the seal on the decline. So what happened before Leak that was the beginning of the fidelity decline? Invention of pentodes and bean tetrodes? Beginning of FB use? Indirect heating of cathodes? Patrick Turner. |
#46
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Phil wrote: Andre Jute wrote: I've read your arguments, Phil. Their subtext is methods to make NFB more usable, less damaging to reproduced sound. That is a legitimate outlook for Otala, who has to fit into an existing industrial environment where NFB is an ineradicable part of that dominant electronics cost-accounting system in which the explicit purpose of NFB is to make cheap parts tolerable. But that has buggerall to do with me as a DIYer. I can afford to take the far simpler, more fundamental course of making my amps so superior in design and components right from the start -- that I can do without NFB and without the damage that NFB does. So I design amps without NFB, period. I shortcut the problem of NFB and eliminate it before it arises. My amps are ultra-silent without NFB; they do not need NFB for any purpose whatsoever. Since one of my ZNFB amps is capable of 80W when in its PSE mode, more than enough to drive electrostatic panels to power-rivetter volume, I take the view that any designer who requires NFB to make his hi-fi amps work has either permitted cost-accountants to bully him, is an impressionable fashion victim, or is too thick to put his mind in gear, tick one or more boxes. The rest is interesting speculation but not of such consuming interest to me that I will spend a morning setting up bench experiments to prove the details of something I already know: that NFB smears the sound. A complete summary of my view on NFB can be found here http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm and here http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm I haven't changed my mind one jot or tittle over the recent discussion. I have heard absolutely nothing that proves a contrary case. That is not to say you may not be right, that the psycho-acoustic effect which gives Class A1 ZNFB (or very low NFB) amps their distinct superiority is a subliminal reaction to the HF phase- smearing in NFB amps that you say Otala posits. I just haven't seen any proof yet, and know that, when I do see such proof, I will consider it of intellectual interest -- and continue to build the sort of ZNFB amps I have always built, in which NFB is excluded for its amplitude smearing at frequencies starting below 100c/s, so that HF phase smearing, if it exists in NFB tube amps, is no danger to my sound. Be fair now, you didn't ask, "Why should I build high feedback pentode amps," But I do build pentode amps, if without the "high feedback". The best amp I ever designed, my Type 114 "Triple Threat" is a PP EL34 with a pentode/ultralinear/triode switch and NFB tunable from zero to about 6dB in the latest iteration but up to 20dB in some early versions. Of course, it is my "best" amp only when operated in the trioded ZNFB mode, but the choice is in the hands of the builder. you asked, "Why do do [no feedback] triode amps sound better?" I merely attempted to give you an answer. You believe that triodes have an internal feedback mechanism, and you wondered why they (still) sound better. My point is a little more subtle. I see an effect which looks like NFB happening between the terminals of a triode; I'm happy to call it internal or natural NFB until someone else offers an explanation that justifies giving it another name; no one offers such an explanation, merely negative objections to naming it NFB; until they pull their finger from their arse and say something positive (and more cogent) than Patrick, who *does* have a case, I shall not change my mind just because they're "agin". You should also understand that some of these clowns are agin not for any good reason but only because it is *me* saying so; Pasternack, for instance, and the usual sockpuppets of the Magnequest Scum, whose disruptive presence on RAT I dispensed with wholesale a few years ago ("Jute is wrong even if he is right, isn't he?" one of them, Ron Bales, complained pitifully!). Pasternack, for instance, has been repeatedly caught out lying on professional matters "in my zeal to flame Andre" -- which is his own sickening excuse in his own words. The basic core of my response/answer is that (1) negative feedback transforms relatively benign amplitude distortion into much less musical phase distortion, and (2) either triodes do *not* have this distortion mechanism, or it occurs at such staggeringly high frequencies that triodes can "get away with it," since the amount of phase distortion produced decreases as the high frequency limit increases. I don't need to go that sophisticated. By far the most popular of my loudspeaker designs (of the published ones; an expensive licensed speak sells amazingly well in the Far East considering the wretchedly high price dictated by the cost of the drivers) is an economy fullranger using a guitar driver, in most installations that I know of with the tweeter disconnected or, on my advice, never fitted. http://members.lycos.co.uk/fiultra/K...Impresario.jpg It has been years since I have been impressed with bandwidth as measure of audio goodness, and I don't just mean excessive bandwidth, I mean the upper end of what is commonly called the "audio spectrum". Most people can't hear it even when they're young. Most people into hi-fi are over middle age; they're lucky if they can hear past 12kHz. In any event, Top C on a piano is a frequency of 4186c/s; over 70% of the energy of that note (over half the decibel value referred to the fundamental's energy) will be in the 2nd and 3rd harmonics, which takes you just past 12kHz. (Try an experiment: filter out everything below the 3rd harmonic of top C, 12558c/s, and listen to what remains. It is horrid, just white noise.) By the way, the same argument of harmonic weight in the production of sound applies to the bass end and well into the midbass: an open G string on a violin played with medium intensity has only 0.1 per cent of its energy in the fundamental -- which is 196c/s; this is the basis for my thesis that the human ear reconstitutes the fundamental from the dominant harmonics, where the energy is. The upshot is that the lower extension of the so-called "audio range" is another engineering chimera that has nothing whatsoever to do with music and everything to do with a bunch of arrogant engineers sitting in a room feeding of each other's testosterone while setting standards that should instead have been set by psychologists or musicologists or, in fact, anyone but engineers. In practice, it means that you can roll speakers off quite high, where the bass will "measure" modestly but sound very, very clean, and they will sound better over the long term than those one-note boof-boff big-bass abominations so beloved of "audiophiles" and "engineers" alike. Peter Walker didn't build his ESL63 any bigger than 45c/s bass (the last pair I measured was 8dB down at 32c/s) because to the ear even a 16c/s organ note, if on the recording at all, will sound startlingly precise because all the energy are in the first two harmonics above the fundamental. More, drivers with a natural high frequency mechanism, like the classic Lowther driver, can sound screechy in the treble precisely because it is not a fundamentally natural noise http://members.lycos.co.uk/fiultra/K...20T91HWAF3.jpg Lowthers with the whizzer tweaked by the insertion of cotton wool behind it or by stiffening with C37, always sound more "natural" even as the measurements start looking less impressive. (I prefer the waterfall anyway, but only after I have run it through a smoothing program because the small glitches are a distraction to the eye but not the ear.) And I proposed a test, which may not work anyway, and which apparently only I have any interest in performing! However, I believe you when you say you already know that feedback smears the sound somehow, and don't need a test to "justify" your decisions, which is a stand I do respect. Hang on a minute. I have demonstrated smearing in the frequency band I'm interested in. I've done it again and again and again, theoretically by mathematics, by measurement with instruments, graphically, and by placebo listening tests (what the pretentious call ABX). http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm I have no problem standing by my taste when taste is the question (for about ten years I was the most widely read music critic in the world with a column syndicated to 9.2m readers every week) but when science has an answer I am as keen as the next man (and clearly keener than the diplomaed quarterwits on RAT) to find the correct answer by the proper scientific method. For a while there, all of us had to face serious criticisms for saying that in our own experience, cables do sound different, Sure, I believe you can hear cables, under two very specific conditions. Again, my conclusion is based on a scientific test. I flew to a different country and in a warehouse spliced huge reels of cable until I had the several of different construction of a length that an engineer (a proper one, not one of the local clowns) calculated for me should be audible by the laws of physics. They were, barely. The other condition under which cables are audible also answers to the laws of physics: when components in the audio chain are mismatched, the resistance and capacitance on a particular cable can make the combination sound better or worse, hence "cable is audible". I personally use Cardas golden section multi-diameter cable because the concept appeals to me: my Impresario speak is designed on Phi, the formulaic base of the golden section. http://members.lycos.co.uk/fiultra/K...Impresario.jpg and it really is a mark of character to stand up and say something that is true, but "officially" stupid. Man, you got enough problems already. You really don't want my character as well: I was sent into exile from my motherland for saying the statistical basis of apartheid was flawed (everyone could see it only twenty years after I said it), and later twice hunted by assassins sent by the apartheid government for a couple of my books. http://members.lycos.co.uk/fiultra/THE%20WRITER'S%20HOUSE.html As an economist I was academically haunted by being the only monetarist in keynesian countries in a keynesian age, as a psychologist in a Freudian age thought very odd, most unreliable, a loose cannon on deck for saying that Freud was a literary giant but didn't know **** about human character. Today, of course, everyone knows I am right and was right then. That was nothing to the filth heaped on me for saying the Common Agricultural Policy of the European Community was a wasteful abomination, or pointing out that the case against DDT was and is unproven, or that "global warming" is an official lie (I've been saying it since the 1960s when I had a running joke in a satarical newspaper column about the missing hole in the ozone layer). If only the "official" beliefs didn't so often turn out to be the ones that are actually stupid, we could all be mindless sheep, and be better off for it! ;-) Nah, I like being "the most dangerous class", as Lenin called reformers. Sure, the price has been high, but the alternative would have been dull. However, there are sometimes good reasons for more fully understanding something. If we assume for a moment that my analysis -- which is basically my attempt to guess at the rest of what Otala was saying, since I have yet to see the full text -- is correct, then several interesting things follow. First, since a threshold below which we cannot hear phase distortion realistically *must* exist There is no *must* about any threshhold. We're discussing the known preference for Class A1 triode sound by an important niche of knowledgeable audiophiles -- despite the known fact that it measures worse than the alternatives on quite a few parameters. Even if those parameters are at present driven to ludicrous lengths by the engineers, it is clear that the highest level of triodes -- DHT, ZNFB, SE or Class A1 trioded ZNFB PP pentodes -- will never come within a magnitude of current technology, at least not on the meter. The preference must be explained by some subliminal effect. The problem with subliminal effects is that they recede with experience, that is, that they're educable; for instance, the limit at which distortion now becomes audible is lower than it was when Olsen first studied the subject 70 years ago. -- and again, for Patrick's benefit, this is phase-smearing, and *not* the simple phase shifting which feedback does correct -- we should be able to add some feedback and get "all gain, no pain." You're still on someone else's agenda, trying to make NFB usable. My amps started sounding brilliant the day I rejected NFB on principle. Patrick said that he added 6 dB to lower output Z, and it sounded fantastic, as opposed to a 20 dB version of the same amp. Hang on a minute. Patrick said that he found that 6dB of NFB didn't degrade the sound audibly -- a matter of taste for him and his client which we must permit them to enjoy in peace; I shall just say I tend to believe that 6dB is very likely a common audibility limit. Patrick also made the point that the NFB lowers the output impedance, on which he puts a high priority *because he builds amps for sale, often to be used with unknown speakers". Anyone who can design his speakers first can also design them so that output impedance and the consequent need for NFB is less; amps can be designed to be speaker-friendly without NFB as long as you know from the beginning that NFB will be excluded. Well, maybe this is completely true, but if we *know* that it is true, then, for example, amps that use high-mu transmitter tubes with positive grid drive and a bit of feedback to get the Zout down begin to make sense, Been there, done that. You're still on someone else's agenda, this time "mo' powa' is betta powa'". It's bullcrap. Even at the lower end of the same argument, a 211 doesn't sound nearly as good as an 845 when both are built to give the same power, simply because the 211 must be driven across the 0V bias line into A2 while the 845 stays strictly in A1. It's another example of a subliminal effect on the ear when very little difference shows on the measuring instrument. especially when the feedback is used in a two-stage configuration that does not include the output transformer, meaning that it can have a *very* high upper frequency limit (you don't need to "dumb down" a stage like you often need to do with a three-stage to prevent oscillation), which limits the damage feedback can do to sub-threshold levels. Many people report that they LOVE the sound of these things, but an unjustified, in this case, bias against *any* use of feedback could prevent us from even trying one. No. This isn't a bias against NFB. This is a preference for staying in Class A1. Or, let's look at the home builder who wants to make a solid state amp -- what the hell -- or at least one with a SS output stage. Sander swears by his hybrid amps. I play SS amps often; the one I like best is the Quad 405 Mk II, because it is so livable. You might check Google for the threads when Stewart Pinkerton, a Poopie Stevenson type clown but with a smidgin more class, challenged me to a design contest. In theory he was supposed to design a silicon amp to beat my 300B SE amp, or at least produce something that sounded close to it. http://members.lycos.co.uk/fiultra/T...trafi-crct.jpg http://members.lycos.co.uk/fiultra/T44bis-'Populaire'-crct.jpg Even with months of help and coaching from John Byrns and Patrick Turner, what Pinko produced was such a botch that not even he wanted to build it. Bored with waiting for the interminable process to run its fractious course, I designed my own simple SS amp and showed how it could be developed to sound something like a good tube amp by driving it into class A. I'm playing it right now. Thanks for reminding me to plug it in and try it again; for the cost it can't be beat! http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm http://members.lycos.co.uk/fiultra/K...20mGBschem.jpg http://members.lycos.co.uk/fiultra/K...%20mGBmatr.jpg http://members.lycos.co.uk/fiultra/K...%20NoBleed.jpg Basically, I'm saying that, if there is phase-smearing as you claim, I also think you're right, that it will be inaudible. I am more interested in what is audible, even if only subliminally. The rest is of theoretical interest and my time is limited. Thanks for the entertainment. Andre Jute More at http://members.lycos.co.uk/fiultra/JUTE%20ON%20AMPS.htm and http://members.lycos.co.uk/fiultra/T...mp%20INDEX.htm There are basically two forms of feedback, the normal one, and the "active-error" version described by J. R. MacDonald and others. The active-error version only "corrects" the output when an actual error exists, whereas the standard version has to correct the open-loop gain even when the load is a steady resistance and the devices are behaving with perfect linearity. If tests show more phase-smearing with the standard version than with the active-error version, well, I know which version I would want to use, or have in a new television. As a bit of a side note, with better sounding SS output stages, maybe we can more easily hear the advantage, assuming one exists, of using a tube to produce the error signal (a tube doesn't have poor quality parasitic capacitances to potentially mess up the low level information). All of this may sound like something only of interest to home builders, but at least some manufacturers actually would be happy to produce noticeably better sounding products, if they could do so for about the same money! If EE's in general become aware of the full characteristics of feedback -- and if home builders start to do this, many EE's and high end manufacturers will indeed follow, eventually -- then we might actually see better products in cars and TV's. No, I'm not saying do this so that we will get better products, but a good understanding of what is needed to make better audio products does tend to help everyone, sooner or later. Low output Z triodes are in fact the theoretically best audio devices at this time, sound-wise, but they require an expensive, heavy, big, high quality output transformer, and that will always limit their use. Or, maybe someone just wants to write an article for AudioXpress about the true nature of feedback, and how to best use it, if its use cannot be avoided! Phil Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review Phil wrote: Andre Jute wrote: In an effort to be agreeable, I tried hard to give you negative feedback inside the tube as an explanation of the overwhelming superiority of triodes (or trioded pentodes) for audio reproduction, among other reasons because NFB is accessible to many who belong on RAT and is a genetic deformity of the silicon scum whose only purpose on RAT is dissension. NFB is what the silicon slime abuse to make their inadequate components sound passable, and what even tubies inspired by the age of sophisters and cost-accountants use to linearize pentodes. NFB thus has a base level of familiarity which gives it a head start in any black box model intended to explain something to diplomaed quarterwits among the silicon slime as well as the better-educated kibbitzers in my own camp. But fine, you want to reject my explanation, then you must offer a better reason to explain why triodes are such superior amplification devices to anything else, so much more pleasing to the ear, so much more accurate to the cultivated taste. Despite my cracks about the metaphysics of tubes, there *has* to be an electrical reason for the superiority of triodes. But sure, all kinds of input is welcome. Andre Jute Andre, I think you are too quick to dismiss the idea that feedback transforms amplitude distortions into phase-smearing, like Otala claimed in his talk/paper (assuming a paper ever followed the talk!). When Patrick was defending feedback, he mentioned that poorly designed amps sound like crap when they have lots of feedback, but that if you fix them up a bit, meaning get rid of much of their excessive nonlinearities -- read, *amplitude* nonlinearities -- then adding feedback sounds okay. Now, if we eliminate the idea that feedback produces random noise -- and we *know* that it reduces amplitude non-linearities -- then the only distortion mechanism left, I believe, is phase-shifting. However, I want to describe the usual "constant 20 degrees phase lag at 40 KHz" as "phase-shifting," and a dynamic, microsecond to microsecond shifting back and forth of one frequency relative to another as "phase-smearing," or "time-smearing." What Otala was saying is that applying feedback to circuits with lots of open-loop distortions, which are (I believe) almost always amplitude distortions, converts these distortions into a back and forth smearing of the high frequencies relative to the low frequencies (and it may smear both in terms of the delay through the amp). Nor can we assume that this time-smearing is a simple function of the low frequency amplitude, because it is probably proportional to the magnitude of the distortions, as well as the LF amplitude: VERY non-musical. When enough feedback is applied to badly designed amps, the amplitude distortions become quite small, so why did Patrick find that they sounded much worse than the same amp sounds when touched up enough to reduce the larger open-loop amplitude distortions? As you say, *something* is wrong, and if it isn't high amplitude distortions (it can't be), and if feedback doesn't produce spurious noises, then the only thing left is exactly what Otala said, time-smearing. In essence, feedback *connects* two things that are normally separate in an amp, namely amplitude distortions, and phase-smearing. It achieves a balance between these two, a balance which is determined by the speed of the amp, the amount of feedback, and the amount of amplitude distortion. Contrary to what you say, Otala was *not* referring to TIM, and transistors did not become so much faster after 1980 than the ones used in his '73 article to make the problem he described go away. Yes, the amps had to be designed well enough to avoid TIM, but that was not a real problem even in '73 *if* you knew what you were doing. The problem he described in '80 was quite different, and even high MHz tubes are subject to it. The interesting things, assuming that feedback problems are indeed time-smearing (regardless of whether this comes from the conversion of amplitude distortions), are one, a single tone will reveal nothing of this, giving very low THD numbers, and two, multiple tones should show something, although looking at it in the amplitude realm will only show higher than expected IMD. There should be a fairly easy way to test to see if this really produces time-smearing. In general, we put a 4 volt 60 Hz signal and a 10 mV 20 KHz signal into an amp with lots of feedback, preferably using non-linear sections of the amplifying devices (say, use two 12AX7 type triodes where the plate curves vary from widely spaced to closely spaced, and use about 60 to 80 dB of feedback to get the overall gain down to 1). Use a high pass filter to see only the 20 KHz signal, and use the 20 KHz signal from the generator to trigger the 'scope. If time-smearing exists, then the 20 KHz signal will appear "fuzzy" on the scope, since it is being shifted back and forth. Repeat without the 60 Hz signal to make sure the time-smearing isn't coming from somewhere else, and then also divide the output from each tube down so that you get the same amplitude output *without* using feedback, and see if the time-smearing goes away. Finally, if possible test over a region where the curves are fairly linear, to see if that also reduces the time-smearing. If so, you have proof that feedback transformed the amplitude distortion into time-smearing. I will try to do this, but I have little time, less energy, and not the best test bench in the world, so it may be a while! If you or someone else both can and wants to try this, I suspect we will get an answer much faster than if I do it. Note that we can use pentodes or transistors, too, but using solid state has the disadvantage of possibly introducing other complications due to the poor quality silicon parasitic capacitances. Also, I am suggesting the use of very different magnitudes as well as frequencies for the two signals, in case equal magnitudes somehow avoids this problem, or at least masks it from this test. And again, contrary to what Patrick said, the idea that *if* this were true, then by now someone would have already tries it, and the results would have become widely know, is just naive. The human race simply isn't that intelligent, at least not yet. An interesting conclusion, assuming this feedback time-smear mechanism exists, is that the output of a feedback amp does *not* match the input when multiple signals exist! However, our normal tests cannot see this, since they tend to focus on one frequency at a time. I believe that Patrick, as well as Otala, said that using local feedback to achieve good open loop linearity, combined with some global feedback, tends to sound pretty good. This makes sense for two reasons, first because although the local feedback will produce phase-smearing, it does so at *very* high speed, which I believe directly reduces the amount of smearing (common sense says that as the speed of devices approaches infinity, feedback becomes "perfect"). Second, the result does contain some mis-match between input and output, even given the high speed of local feedback, but now the global feedback will not only reduce the remaining "normal" amplitude distortions, it should also reduce the time-smearing produced by the local feedback, since this time-smearing will still produce an error signal for the global feedback. Of course, this reduction in time-smearing will itself produce more time-smearing, but it should be a case of 0.1 x 0.1 = 0.01, so the final degree of time-smearing is reduced by "dividing up" the total feedback into local plus global. Finally, you saw the review of Otala that Phil Allison gave, and I think you were as impressed by it as I was (although it looked bad to PA). When a man who was as talented, knowledgeable, and honest as Otala produces a PROOF that negative feedback *always* transforms the amplitude distortions of the open loop into phase smears of the closed loop, we should not dismiss it as simply a problem of "old devices," a problem that a slight increase in speed can make go away, especially when the discussion that led to his analysis (the Audio Critic BS session) included a lot of talk about vacuum tubes, and how their speed advantage made it easier to use them with feedback. We really should do at least one or two tests before dismissing his conclusions. Again, I will try to do so, but if you want to know anytime soon, you should probably rely on someone else. Phil |
#47
Posted to rec.audio.tubes
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The day the worm started gnawing HI-Fi was Explanation still required for triode superiority
Patrick Turner wrote: Somebody said, and Andre replied..... Modeling and analysis are essential; but the map is not the world. Actually, the only °essential* is having some method of deciding where you want to arrive. High fidelity went wrong long before Mr Leak's inspired marketing terminology (Point One) became an engineering article of faith, but that set the seal on the decline. So what happened before Leak that was the beginning of the fidelity decline? Invention of pentodes and bean tetrodes? Beginning of FB use? Indirect heating of cathodes? Patrick Turner. Pick any of those, Patrick, or of these: the start of the search for power, speakers becoming more insensitive, gramophone records becoming cheap enough to be everyday items for everyman with the consequent proliferarion of cheap gramophone consoles, and no doubt a long, long list of other factors someone may wish to add. Or, if you're into icon-smashing, choose the day Theo Williamson showed the world how to use NFB competently to get a *lot* of power without paying the electrical price, Hafler and Keroes on their finest day (this is again about power and NFB), CFB from Walker and Williamson (again, about more power for less cost). It is all a matter of where you're looking from. You might, for instance, consider the Williamson and then the Quad II as the zenith of hi-fi, with a long cheapening decline into silicon; it is an equally valid view (and depends, always, on which speakers you have in mind to use with their amps...). In general, these men were driven by external events in a marketplace, and it is in the external events we must seek our answer. Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review |
#48
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Explanation still required for triode superiority
What's nice about the colt is that it's relatively hard to just pull
the trigger without a clip. Kid - wise, that is. Of course a safe or lock is the best prevention, but with the Colt without a clip: first, the clip has to be located and insterted. Not too hard. then a round has to be chambered by physically pulling the slide back with one hand. The weapon can't be pushed into the ground to pull the slide back. Extremely hard for young hands. Teenagers are another story, of course. Then a handgrip safety must be depressed before the trigger unlocks, made for a grown hand. To an experienced shooter, all these things are second nature and can be done within a second. A revolver can be fired by anyone just by pulling the trigger. Another nice thing about the semi-auto is that if you can't find the clip, it's hard for someone else to see that there's no ammo in it ; ) Stuart Krivis wrote: On Wed, 27 Sep 2006 02:20:39 GMT, Chris Hornbeck wrote: personal confrontations is simply the size of the bore; anybody who's ever looked at the receiving end of a pistole seems to remember (and mentally inflate) the bore. Revolvers are even better at this because they also show all the bullets aimed at you. And, worst case, ya still gotta knock the ****er down enough to allow ya to do some serious kicking. Real people don't just lay down and play dead like in the movies. Yes, it's all about plumbing. You have to put as large and as many holes in the OP's plumbing as you can so that they fall down and stay down. :-) |
#49
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Explanation still required for triode superiority
On Wed, 27 Sep 2006 04:53:47 +0100, Eeyore
wrote: including *all* possible issues, including non-linearities in time and amplitude, and at all levels; I don't see where time comes into it actually. Do feel free to comment on this point. I should have said something more like "relative timing errors", variations in group delay between input and output. Personally, I consider these to be simply time non-linearities, because the mechanisms that interest me are either modulation, or things that map as modulation, including the modulation's IM products. and will happen, for reproduction (not real time) soon. What do you mean by not real time ? Reproduction is inherently "not real time", so processing time (well, less than a week might be nice) is unimportant. Performance is affected by processing time ("latency", as they say nowadays) beyond some threshold. Just a matter of horsepower and Moore's Law, natch. Much thanks, as always, Chris Hornbeck |
#50
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Explanation still required for triode superiority
Chris Hornbeck wrote: On Wed, 27 Sep 2006 04:53:47 +0100, Eeyore wrote: including *all* possible issues, including non-linearities in time and amplitude, and at all levels; I don't see where time comes into it actually. Do feel free to comment on this point. I should have said something more like "relative timing errors", variations in group delay between input and output. In a tube amp, any group delay variation will likely simply be the result of the output transfomer ! In a s-s amp any variation will simply be minute. Personally, I consider these to be simply time non-linearities, because the mechanisms that interest me are either modulation, or things that map as modulation, including the modulation's IM products. It is actually a linear mechanism behind it though. and will happen, for reproduction (not real time) soon. What do you mean by not real time ? Reproduction is inherently "not real time", so processing time (well, less than a week might be nice) is unimportant. Performance is affected by processing time ("latency", as they say nowadays) beyond some threshold. Just a matter of horsepower and Moore's Law, natch. 'Real time' DSP processing is quite easy these days. It may involve a few ms of delay but not much more. Graham |
#51
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The day the worm started gnawing HI-Fi was Explanation stillrequired for triode superiority
Andre Jute wrote: Patrick Turner wrote: Somebody said, and Andre replied..... Modeling and analysis are essential; but the map is not the world. Actually, the only °essential* is having some method of deciding where you want to arrive. High fidelity went wrong long before Mr Leak's inspired marketing terminology (Point One) became an engineering article of faith, but that set the seal on the decline. So what happened before Leak that was the beginning of the fidelity decline? Invention of pentodes and bean tetrodes? Beginning of FB use? Indirect heating of cathodes? Patrick Turner. Pick any of those, Patrick, or of these: the start of the search for power, speakers becoming more insensitive, gramophone records becoming cheap enough to be everyday items for everyman with the consequent proliferarion of cheap gramophone consoles, and no doubt a long, long list of other factors someone may wish to add. If we ignore history, we make a grave mistake. I cannot see that there was ever a period where suddenly hi-fi was established in say about 1930 where we had low thd, good bw, high DF, good SNR, and all without NFB and just a reliance on DHT triodes. Just about every single link in the recording industry as existed before vinyl was pretty damn awful and required listeners to have a few drinks before they could fully ignore the noise & distortions on shellac 78s. Microphones and speakers, including horn types and the calibration of the measurement systems for such items were all rather attrocious. There definately was a need for a tone control in 1935. Either that or an axe, and nobody I ever heard of used a graphic equaliser to flatten the routinely no flat response in just about all attempts to record and replay anything. With amps, the search for power led to a 300B in around 1928 and it was a large improvement on using a pair of 2A3 to get about the same power, although a pair of 2A3 can do 8 watts. The invention of the KT66/6L6 type of tubes meant more folks could have 8 watts with less Pda, but with a lot mote THD and attrociously high DF, so NFB was a must to at least to pull the Rout down to the triode level without loop NFB. Because NFB was something that hardly anyone understood except the boffins in white coats then it couln't much be used because of the ignorance about gain and phase shift. The official % of folks who understand NFB application remains extremely low. Williamson officially defined ways and means to be able to use 20dB of NFB and get away with it without clouds of smoke. Its an arguable point as to whether well applied loop NFB ruins a triode amplifier's sonic performance or not. The jury has been out on this and for the verdict on multigrid guilt since about 1935, no? Or, if you're into icon-smashing, choose the day Theo Williamson showed the world how to use NFB competently to get a *lot* of power without paying the electrical price, Hafler and Keroes on their finest day (this is again about power and NFB), CFB from Walker and Williamson (again, about more power for less cost). Well, the Williamson 16 watt amp didn't depend on its power from two triodes because there was loop FB added. Williamson merely made the power that was available from a pair of class A trioded KT66 into power that was virtually entirely free of any contributing distortion in any audio amp applications. All the other things in the audio chain of 1947 contributed far more grunge to any listening experience than that contributed by the ideas of Mr W. The W amp was a start to cleaning up what was a dirty act; the act of recording something so that replay could not be distinguished from the live performance. He showed what could be done, and engineers have worked ever since to improve the measurements. After having put several zeros in front of the 0.1% thd at 16 watts to get say 0.0001% at 200W, ( Halcro ) exactly what has been achieved? Not much, imho, in amplifiers. Most improvements to audio we experience seem to have occurred in areas elsewhere to that of amplifiers. The modern speaker is, imho, a damn sight better than anything from1947, even though its is more insensitive; seems like a flat response without cone resonance and cone breakup is more readily achieved with the modern approach. Then Walker stepped in with something to bomb everyone, the ESL57. But now we have had clean sources from master tapes and I hate to say it, digital, then we can relax on amps because who really needs to have 0.02% at listening levels when 0.2% is OK? The total system thd including recording and replay gear including speakers can just get under 0.2% at all times, so there isn't any use worrying about a high distortion amplifier making what may have been 4% dreadful in 1947 more dreadful. Some would say this is a cop out and compromise idea, but few folks would recognise whether the global NFB is connected or not in a W amp in a listening test, and especially if the W amp has a quad of KT88/KT90 in triode in its output stage. The Hafler and Keroes ideas about local cathode feedback seem a step forward because when well implemented the result is rather good. And better than Quad II. The Quad II is a nice idea, but really I have never regarded Quad II as any more than a chic toy boy amp needing a shove to get it to grow up. The Quad 40 would have to be a better amp. But well before there was ever to be another tube amp from Quad after Quad II, the world and Quad turned to solid state. There would be many who'd say hooray, and what fine solid state amps were made by Quad, and that any of them can hold their own with anything made now. I leave such people in peace to celebrate; I will still dissappear to gather around me some glassware which I care for enough to keep it on the road without much effort, and without a huge insidious build up of N&D from lack of care. And I prefer the fidelity of tubes and don't care a hoot that the measurement zealots go all foamy at the mouth over numbers, the numbers don't explain the phenomena of tube use being good. It is all a matter of where you're looking from. You might, for instance, consider the Williamson and then the Quad II as the zenith of hi-fi, with a long cheapening decline into silicon; it is an equally valid view (and depends, always, on which speakers you have in mind to use with their amps...). The initial solid state gear was based around germanium. What a horror story it was for 10 years. Then in about 1960, silicon became king overnight. The early germanium and silicon was accepted very eargerly by the public because 2 channel stereo arrived with it, which allowed imaging, another facet of hi-fi. The sound quality from the SS was no worse than the poorly serviced old ageing tube amps people were reluctant to re-tube, service properly, and duplicate for stereo. Many Quad II amps I have serviced in the last 10 years had very serious faults such as one KT66 with 30mA, the other just slightly red with 90mA, and even without this ****ty fault the imbalance of matching of EF86 and KT66 meant that THD was just as if there was no global NFB connected or worse. Sound was very lack lustre indeed. The same can be said for ALL the dear old junk made between 1947 and 1957. In general, these men were driven by external events in a marketplace, and it is in the external events we must seek our answer. Indeed the market place corrupts all ideals; greed rules! But if any here want to take the purist line and make speakers and amplifiers without compromises that were routinely addopted to cheapen a product's cost of production and distribution, then they can do so now. Maybe they cannot ever build a car in their back yard, but they can build a hi-fi system. They still need to find decent recordings to play to enjoy their system, and like the jerks who make some CDs are to blame for dissappointments discerning memebrs of my dad's generation were appalled by some of the vinyl and tape offerings one over spent on. In any collection of vinyl I eagerly accept as gifts now there is a mixture of gems and dross. Patrick Turner. Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review |
#52
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Explanation still required for triode superiority
"Andre Jute" wrote in message ups.com...
My point is a little more subtle. I see an effect which looks like NFB happening between the terminals of a triode; I'm happy to call it internal or natural NFB until someone else offers an explanation that justifies giving it another name; no one offers such an explanation, merely negative objections to naming it NFB; until they pull their finger from their arse and say something positive (and more cogent) than Patrick, who *does* have a case, I shall not change my mind just because they're "agin". The effect you see is the change in plate current with plate voltage. This is exactly the definition of plate resistance, which is both the name and the explanation that have been in standard use for the past seven decades or so. In actual fact there is no external observation you can make of the triode that proves, or even suggests, there is internal negative feedback at work inside the tube. Everything you see can be more simply and economically explained by the Thevenin or Norton models. Thevenin, Norton, and the NFB conjecture are all just fictional models that help to describe or predict the tube's external behavior. None of them represents the actual physical processes at work inside the tube, and it is a mistake to claim otherwise. The Child-Langmuir equation, which is based on the distribution of electric fields and charge density inside the tube is another model, and arguably as good an explanation of tube behavior as we need. There's nothing in it that depends on negative feedback, either. This is fundamentally an engineering debate and the arguments are necessarily framed in engineering terms. The fact that technical language is used to express a point doesn't make the point true by default. The assumptions and inferences have to be grounded in fact and logic to be valid. The challenge is to define who's qualified to decide what is factual and logical in an engineering argument. An engineer perhaps? I would be delighted to debate this subject, point by point, in front of a qualified and neutral judge (or panel of judges) from the tube audio engineering community. How about Steve Bench, John Atwood, Lynn Olson, or Morgan Jones? -Henry |
#53
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Explanation still required for triode superiority
"Impedance is futile, you will be simulated into the triode of the
Borg"... :-) |
#54
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Explanation still required for triode superiority
Thanks for writing in, HP. I happen to agree with you, the model isn't
real life. But it is the nearest we have to the vacuum inside the tube. I've already given this a good bash, and everyone else is bored with it. You can find my conclusions at http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm and http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm If those you want as referees wish to come on RAT to give us the benefit of their wisdom, we should be delighted to welcome them (or welcome some of them back, as Steve for instance is an old RAT). But bringing them here specifically for a contentious debate is simply likely to drive them out again in short order; in fact, I haven't heard a dumber idea all week, and we've had quite a few dillies already. I was entertained by your suggestion that we should believe "an engineer perhaps". Perhaps is right. For every good engineer we get on RAT, we seem to get three rotters. Only recently we had Pinkerton, Krueger and Poopie Stevenson, blustering tenth-raters every one of them. The rot on RAT set in with one Henry Pasternack, who bragged about a master's degree in electronics from Stanford; this clown Pasternack was so thickly unscientific that in our first exchange I caught him out by trailing before him 90 plus observations on 30 plus amps -- *which he never asked to see*; he didn't even discover for another ten months why the decent engineers were treating him with disdain. See the section WHO HAS A "FULL UNDERSTANDING"?, when you get to: http://groups.google.ie/group/rec.au...af253a7e070591 Pasternack was the "engineer" locally known as Pompass Plodnick, for the obvious reasons; he's also the one who notoriously tried to excuse lies on professional matters as merely (!) "my zeal to flame Andre". You can see why after our experience with Pasternack, the very paradigm of a diplomaed quarterwit, we now expect more proof of scientific and personal honesty from an engineer than merely that he waves a diploma. Hang around, HP; start a bit smaller than such contentious subjects as NFB and triode superiority -- and you might even last longer than a week. A sense of humour and a copy of the RDH helps. Don't let the RDH frighten you off by its size; see my article here for a guide on which parts of the RDH you need to read: http://members.lycos.co.uk/fiultra/J...MPS%20RDH.html Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review HP wrote: "Andre Jute" wrote in message ups.com... My point is a little more subtle. I see an effect which looks like NFB happening between the terminals of a triode; I'm happy to call it internal or natural NFB until someone else offers an explanation that justifies giving it another name; no one offers such an explanation, merely negative objections to naming it NFB; until they pull their finger from their arse and say something positive (and more cogent) than Patrick, who *does* have a case, I shall not change my mind just because they're "agin". The effect you see is the change in plate current with plate voltage. This is exactly the definition of plate resistance, which is both the name and the explanation that have been in standard use for the past seven decades or so. In actual fact there is no external observation you can make of the triode that proves, or even suggests, there is internal negative feedback at work inside the tube. Everything you see can be more simply and economically explained by the Thevenin or Norton models. Thevenin, Norton, and the NFB conjecture are all just fictional models that help to describe or predict the tube's external behavior. None of them represents the actual physical processes at work inside the tube, and it is a mistake to claim otherwise. The Child-Langmuir equation, which is based on the distribution of electric fields and charge density inside the tube is another model, and arguably as good an explanation of tube behavior as we need. There's nothing in it that depends on negative feedback, either. This is fundamentally an engineering debate and the arguments are necessarily framed in engineering terms. The fact that technical language is used to express a point doesn't make the point true by default. The assumptions and inferences have to be grounded in fact and logic to be valid. The challenge is to define who's qualified to decide what is factual and logical in an engineering argument. An engineer perhaps? I would be delighted to debate this subject, point by point, in front of a qualified and neutral judge (or panel of judges) from the tube audio engineering community. How about Steve Bench, John Atwood, Lynn Olson, or Morgan Jones? -Henry |
#55
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Explanation still required for triode superiority
robert casey wrote: "Impedance is futile, you will be simulated into the triode of the Borg"... :-) Reluctance will not be tolerated. Graham |
#56
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Explanation still required for triode superiority
HP wrote: "Andre Jute" wrote in message ups.com... My point is a little more subtle. I see an effect which looks like NFB happening between the terminals of a triode; I'm happy to call it internal or natural NFB until someone else offers an explanation that justifies giving it another name; no one offers such an explanation, merely negative objections to naming it NFB; until they pull their finger from their arse and say something positive (and more cogent) than Patrick, who *does* have a case, I shall not change my mind just because they're "agin". The effect you see is the change in plate current with plate voltage. This is exactly the definition of plate resistance, which is both the name and the explanation that have been in standard use for the past seven decades or so. In actual fact there is no external observation you can make of the triode that proves, or even suggests, there is internal negative feedback at work inside the tube. Everything you see can be more simply and economically explained by the Thevenin or Norton models. Thevenin, Norton, and the NFB conjecture are all just fictional models that help to describe or predict the tube's external behavior. None of them represents the actual physical processes at work inside the tube, and it is a mistake to claim otherwise. The Child-Langmuir equation, which is based on the distribution of electric fields and charge density inside the tube is another model, and arguably as good an explanation of tube behavior as we need. There's nothing in it that depends on negative feedback, either. Professor child called the mutual effect of anode AND grid voltages in a triode a form of "self regulation". See Radio Engineering, by Terman, 1937. He does not call it NFB probably because it would have confused ppl at the time who were used to NFB ONLY being some external networking to get an amp of device to display lower Ra thd etc than otherwise it would without NFB. The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. When you have a 300B with Ia = 70mA, Ea = +400V, then if it acted like a resistor without NFB the R value would be 400 / 0.07 = 5,700 ohms. But where one maintains the grid bias voltage and fixes the cathode voltage, abd simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. One simply cannot deny that a huge anode feedback effect exists, and where you have a grid also able to control the Ia with a gm of about 5mA/V then there MUST be a summing of the anode and grid voltage effects according to some formula ( upon which Professor Child throws more light than I do ) . So its very easy to see that NFB is alive and operational in a triode. Because its self contained, there is no need to always represent the triode with symbols to represent the NFB network that exists, it merely is represented by the normal symbol but considered with Ra, µ, and gm WITH NFB being effective; Thge triode cannot be considered without its NFB unless one makes a mental model of a perfect pentode with NFB. The perfect pentode BTW is an unusual animal because it'd assume Ra would be infinite, and since µ = gm x Ra, then perfect pentode µ also would be infinite, so that a mild external loop of NFB would render such a pentode circuit free of any THD because the gain reduction with NFB would also be infinite. But alas, no such perfect pentode exists. The anode voltage still always has some effect on the Ia even with a screen present. This is fundamentally an engineering debate and the arguments are necessarily framed in engineering terms. The fact that technical language is used to express a point doesn't make the point true by default. The assumptions and inferences have to be grounded in fact and logic to be valid. The challenge is to define who's qualified to decide what is factual and logical in an engineering argument. An engineer perhaps? I am not a qualified university educated triodologist. But my powers of observation reveal NFB in triodes to me. But by exactly what process in purely technical terms would you use to allege NFB does NOT exist in triodes? I would be delighted to debate this subject, point by point, in front of a qualified and neutral judge (or panel of judges) from the tube audio engineering community. How about Steve Bench, John Atwood, Lynn Olson, or Morgan Jones? The above list may not wish to join our little discussions because the morons and arsoles wait impatiently with buckets of **** to drench any attempts of true intellectual discourse and democracy. Patrick Turner. -Henry |
#57
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Explanation still required for triode superiority
Le 25 Sep 2006 12:51:12 -0700,
"Bret Ludwig" a Ă©crit : Peter Wieck wrote: Andrew Jute McCoy wrote its usual fallacious arguments: Called "begging the question". Triodes are neither "superior" nor "inferior" when it comes to amplifiers. However, they do have many difficulties. Not the least of which a Flea Power. Expensive to create. Difficult to make operational (as your model so clearly illustrated). Triodes are cheaper to build than beam power tubes of a given size, simpler, and can be used for amplifiers of any size. Most 50 kW AM broadcast transmitters had two triodes in their modulators giving 30 kW audio power in Class B. The common 811 available under $20, though not an ideal tube, can give 200 easy watts for a pair. As can 211s, 845s, etc. The GEC book shows a 1 KW audio amp with a pair of largish glass triodes. Difficult to use? Just give them a filament supply of several amps, preferably from a filament transformer with shunts designed for that tube, a few kV on the plate and enough drive and they work fine. Audio is not only about power and characteristics on the paper, but about sound. Most if not all high power tubes are designed for high frequency transmitters, not for high-fidelity, and they will sound very poorly when used for an audio amp. You will get a much better sound when using 4, 6 or 8 EL34 or 300B as only 2 more powerful tubes. Now, the controversy between pentode and triode is not new. If you look, most of the so called pentodes used in high fidelity audio are in fact beam-tetrodes. The main problem with the pentode is its high output impedance. The main problem with the triode is its low sensibility. The beam tetrode try to get most of the advantages of the triode as its relatively low output impedance and most of the advantages of the pentode as its high sensibility. And the result is a very good tube for power amplification. But if you want to get a good result in audio with a beam tetrode, you must be very careful with the design. A triode design is easier because you don't have the g2. A good practice, if you are using a fixed g2 voltage, is to stabilize it. Just be doing it, the amp will archive at least a 2 time better dynamic at the output. But how many amps on the market are using a stabilized Vg2? Almost no one because it cost more money to build. Another issue, and not only with the beam tetrode, is the quality of the tubes. Take the 6L6. It is hundred of different brands, but only a little part of those brands have a really good quality of manufacturing. It is in theory the same tube as a 807. Make an amp with 2 x 807, 600V DC on the middle of the output transformer when the amp is at full output, 300 V DC on the g2, and replace the 807 by 6L6 tubes. Most of them will just glow up at full output. And already at low level, they will arc inside the tube because of a too high Va, and this will sound like hell in the loudspeaker. Take a preamp tube as the ECC83-12AX7. Buy a few tubes of different brands. You will get as many sound at the output as brands. In fact even more, because with the cheaper brands, different tubes will sound differently. So, when you want to compare tubes, you must not only say the type of the tubes, but the brand too. And when comparing tubes as different as a triode and a pentode, you must talk about the topology of the circuits. A good quality pentode will sound better as a poor quality triode. And a pentode used in a deign that have a good topology will sound better as a triode of the same quality but used in a circuit with a poor design. -- Dominique Michel |
#58
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Explanation still required for triode superiority
Patrick Turner wrote:
[snip] Professor child called the mutual effect of anode AND grid voltages in a triode a form of "self regulation". See Radio Engineering, by Terman, 1937. He does not call it NFB probably because it would have confused ppl at the time who were used to NFB ONLY being some external networking to get an amp of device to display lower Ra thd etc than otherwise it would without NFB. The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. When you have a 300B with Ia = 70mA, Ea = +400V, then if it acted like a resistor without NFB the R value would be 400 / 0.07 = 5,700 ohms. But where one maintains the grid bias voltage and fixes the cathode voltage, abd simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. One simply cannot deny that a huge anode feedback effect exists, and where you have a grid also able to control the Ia with a gm of about 5mA/V then there MUST be a summing of the anode and grid voltage effects according to some formula ( upon which Professor Child throws more light than I do ) . So its very easy to see that NFB is alive and operational in a triode. [snip] I am not a qualified university educated triodologist. But my powers of observation reveal NFB in triodes to me. But by exactly what process in purely technical terms would you use to allege NFB does NOT exist in triodes? Patrick, you're simply being stubborn at this point. We have pointed out, over and over, that a plate resistance, which, so far, you CANNOT and HAVE NOT proven does not exist, can account for all of the "feedback effects," by which you mean damping, that you talk about. Yes, in the absence of tests which possibly can distinguish between anode resistance and triode feedback, we really don't know which it is. But to claim that feedback must exist *because* effects equivalent to either feedback or low plate resistance exist is unscientific. You have a choice, and that is why the rest of us simply state that, in the absence of any logical, intellectual, or engineering advantage for feedback, we prefer low plate resistance as a *model*. That's our choice. Maybe the other choice is better. But you have not given any analysis to my knowledge which proves that such a choice does not exist, or even that a feedback model is a better choice for audio or electronics. Phil |
#59
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Explanation still required for triode superiority
Hi, Dominique. Welcome to RAT. I'm Andre Jute. This is my thread.
You say: The main problem with the triode is its low sensibility. Actually, the great advantage of the triode (or trioded pentodes like the EL34) is its *high* sensibility with the music, that is the natural, unaffected way it reproduces it. You probably mean "low power". That mainly bothers people who haven't put their minds in gear. Once you have sensitive speakers, 300B are overkill on Lowther horns already. Alternatively, when I wanted a triode single-ended amp to drive Quad ESL63, I built it with transmitting triodes to give 80W from a standard 2Vrms CD output (417A::300B::PSE SV572-3 or -10 does the biz in only three ZNFB stages). If you're willing to pay the price, everything is possible and nothing is a barrier. As examples of why the low power of the commoner triodes is not a problem, here are some bicor horns I built for Lowther drivers: http://members.lycos.co.uk/fiultra/K...20T91HWAF3.jpg to use with either of these 300B http://members.lycos.co.uk/fiultra/T...trafi-crct.jpg http://members.lycos.co.uk/fiultra/T44bis-'Populaire'-crct.jpg but here is 0.3W quality amp that drives the Lowthers very pleasingly indeed: http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg http://members.lycos.co.uk/fiultra/t...17acircuit.jpg http://members.lycos.co.uk/fiultra/t68bismzlayout.jpg or if you want good quality and more power for less money, here is a 2W trioded EL34 amp I designed for students: http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg to use with this inexpensive but very sensitive (and sensible!) speaker: http://members.lycos.co.uk/fiultra/K...Impresario.jpg All becomes clear when you give up being a fashion-victim of people who think more power is better power because they are too lazy or stupid to design within the parameters of the best-sounding components; some are too thick even to work out that it is the sound that matters, not the engineering, and of those we have a surplus already on RAT. You might enjoy "The myth of the Watt:", or then again, not, as the case might be: http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm More on my main site, URL under my sig. Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review Dominique Michel wrote: Le 25 Sep 2006 12:51:12 -0700, "Bret Ludwig" a écrit : Peter Wieck wrote: Andrew Jute McCoy wrote its usual fallacious arguments: Called "begging the question". Triodes are neither "superior" nor "inferior" when it comes to amplifiers. However, they do have many difficulties. Not the least of which a Flea Power. Expensive to create. Difficult to make operational (as your model so clearly illustrated). Triodes are cheaper to build than beam power tubes of a given size, simpler, and can be used for amplifiers of any size. Most 50 kW AM broadcast transmitters had two triodes in their modulators giving 30 kW audio power in Class B. The common 811 available under $20, though not an ideal tube, can give 200 easy watts for a pair. As can 211s, 845s, etc. The GEC book shows a 1 KW audio amp with a pair of largish glass triodes. Difficult to use? Just give them a filament supply of several amps, preferably from a filament transformer with shunts designed for that tube, a few kV on the plate and enough drive and they work fine. Audio is not only about power and characteristics on the paper, but about sound. Most if not all high power tubes are designed for high frequency transmitters, not for high-fidelity, and they will sound very poorly when used for an audio amp. You will get a much better sound when using 4, 6 or 8 EL34 or 300B as only 2 more powerful tubes. Now, the controversy between pentode and triode is not new. If you look, most of the so called pentodes used in high fidelity audio are in fact beam-tetrodes. The main problem with the pentode is its high output impedance. The main problem with the triode is its low sensibility. The beam tetrode try to get most of the advantages of the triode as its relatively low output impedance and most of the advantages of the pentode as its high sensibility. And the result is a very good tube for power amplification. But if you want to get a good result in audio with a beam tetrode, you must be very careful with the design. A triode design is easier because you don't have the g2. A good practice, if you are using a fixed g2 voltage, is to stabilize it. Just be doing it, the amp will archive at least a 2 time better dynamic at the output. But how many amps on the market are using a stabilized Vg2? Almost no one because it cost more money to build. Another issue, and not only with the beam tetrode, is the quality of the tubes. Take the 6L6. It is hundred of different brands, but only a little part of those brands have a really good quality of manufacturing. It is in theory the same tube as a 807. Make an amp with 2 x 807, 600V DC on the middle of the output transformer when the amp is at full output, 300 V DC on the g2, and replace the 807 by 6L6 tubes. Most of them will just glow up at full output. And already at low level, they will arc inside the tube because of a too high Va, and this will sound like hell in the loudspeaker. Take a preamp tube as the ECC83-12AX7. Buy a few tubes of different brands. You will get as many sound at the output as brands. In fact even more, because with the cheaper brands, different tubes will sound differently. So, when you want to compare tubes, you must not only say the type of the tubes, but the brand too. And when comparing tubes as different as a triode and a pentode, you must talk about the topology of the circuits. A good quality pentode will sound better as a poor quality triode. And a pentode used in a deign that have a good topology will sound better as a triode of the same quality but used in a circuit with a poor design. -- Dominique Michel |
#60
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Explanation still required for triode superiority
"Patrick Turner" wrote in message ...
HP wrote: I've corrected the ID in my news client profile. Professor child called the mutual effect of anode AND grid voltages in a triode a form of "self regulation". See Radio Engineering, by Terman, 1937. I've read that book in the library, but don't have a copy of my own, so I can't really say for sure out of context what Terman meant by "self regulation". In the past, I've responded to this point by giving examples of systems that can be called "self-regulating", but where the regulation is the result of a dynamic equilibrium rather than negative feedback. The spinning electric motor and the falling parachute are two examples, but many others can be proposed. I've also shown before how models of rate-limited systems, like the electric motor or even a plain resistor, can be refactored into equivalent negative feedback systems. But the feedback models don't add any information that we can't, in general, get from simpler models, and with much less effort. The same is true of triodes and feedback. Norton and Thevenin have the same predictive power as the feedback model, but are simpler and more useful. Please take note, I'm not arguing that the triode cannot be described in terms of negative feedback. What I am arguing is that this is a contrived and largely pointless complication. I am also showing how other models, both external and internal, can give us the same information about the tube without the need to invoke negative feedback. Finally, I am pointing out the inconsistencies, errors, and omissions in your own statements. The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. When you have a 300B with Ia = 70mA, Ea = +400V, then if it acted like a resistor without NFB the R value would be 400 / 0.07 = 5,700 ohms. But where one maintains the grid bias voltage and fixes the cathode voltage, abd simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. You get the exact same result if you represent the tube as an 800 Ohm resistor in series with a 344V battery, and no feedback is required. This is the Thevenin model. While your result is not inconsistent with feedback, the existence of an alternate model means your results cannot "prove" there is NFB in the triode. As I keep saying, any attempt to "prove" the existence of NFB in the tube by external observation is fallacious from the get-go. You should read and think about this carefully because it's a fundamental point. One simply cannot deny that a huge anode feedback effect exists, and where you have a grid also able to control the Ia with a gm of about 5mA/V then there MUST be a summing of the anode and grid voltage effects according to some formula ( upon which Professor Child throws more light than I do ) . So its very easy to see that NFB is alive and operational in a triode. But I certainly can deny it. I hope you'll agree the mechanism at work here is the same even if we impose the condition of linearity. And if this is true, then by the principle of superposition we can separate out the effects of the control grid and the plate and analyze them separately. The control grid, clearly, is analgous to the non-inverting input on the op-amp. It's in the forward path, so we can ignore it. In fact, we can tie the control grid to the cathode, or remove it entirely, and the analysis stays the same. And this takes us back to the diode argument and your inconsistent interpretation of plate resistance. Your observation about the summing of the effects of the control grid and the plate is really the crux of your argument because it's the only statement you've ever made to justify that negative feedback occurs. But the argument can't be valid, as I've shown, because it fails to acknowledge the principle of superposition. Superposition says that the summing is irrelevant because the effects of the grid and the plate can be treated separately. This is why the point about the diode is so important. Thee triode cannot be considered without its NFB unless one makes a mental model of a perfect pentode with NFB. This isn't true at all, and is a perfect example of "begging the question", or taking the conclusion of an argument as one of its premises. We are trying to evaluate the claim that triodes have internal negative feedback. Declaring, a priori, that a pentode is a triode with negative feedback removed, and showing that adding feedback to the pentode transforms it into a triode begs the question since it depends on the presumption that the triode had negative feedback in the first place. The simple, non-feedback explanation for triode behavior is as follows. The plate voltage establishes an electric field, and therefore a potential gradient, at the surface of the cathode that draws electrons out of the cathode and sweeps them toward the plate. The electrons are rapidly emitted into the vicinity of the cathode until the potential gradient, by Poisson's equation, reaches zero. At this point, the net rate of electron emission from the cathode equals the rate at which electrons are swept to the plate and the plate current settles into a steady equilibrium. Increasing or decreasing the plate voltage throws the system out of equilibrium and the plate current varies upward or downward until the equilibrium is reestablished at a new operating point. You can call this negative feedback if you want and you won't be incorrect. But in doing so, you should be prepared to accept that many, many other natural systems are also examples of negative feedback, not the least of which is the lowly vacuum diode. You also won't be excluding interpretations that do not depend on the presumption of feedback. [Pentode coments deleted] Irrelevant. I am not a qualified university educated triodologist. True. I would never say that someone needs a university degree to learn to build audio gear. You are a perfect case in point, Patrick, how someone without a Triodology degree can become an accomplished tube technician and a prolific designer. But you need to understand, no matter how broad your practical experience may be, that there are limits to your conceptual knowledge. For instance, your example with the 300B above tells me you are confused about the difference between small-signal and large-signal circuit analysis. This isn't a minor error, either. It's a giant, sucking hole in your argument. But my powers of observation reveal NFB in triodes to me. Yes, and to a fundamentalist Christian, the diversity of species reveals the wonder and glory of creation and thereby proves the existence of God. But that doesn't qualify him to be a biologist (much as he may think so). But by exactly what process in purely technical terms would you use to allege NFB does NOT exist in triodes? I believe I've answered that question many times over the past few days. I can't help you if you didn't understand. I have a rule I call the "Law of Conservation of Complexity". It says for any given topic there is a lower bound to how simple a valid explanation can be. If the audience lacks the sophistication to follow along at that level, than no explanation, no matter how correct and clear, will ever make sense to that audience. The above list may not wish to join our little discussions because the morons and arsoles wait impatiently with buckets of **** to drench any attempts of true intellectual discourse and democracy. On that point, you won't get any disagreement from me. Although we might not see eye-to-eye when it comes to assigning blame to specific individuals. -Henry |
#61
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Explanation still required for triode superiority
Dominique Michel wrote: Le 25 Sep 2006 12:51:12 -0700, "Bret Ludwig" a Ă©crit : Peter Wieck wrote: Andrew Jute McCoy wrote its usual fallacious arguments: Called "begging the question". Triodes are neither "superior" nor "inferior" when it comes to amplifiers. However, they do have many difficulties. Not the least of which a Flea Power. Expensive to create. Difficult to make operational (as your model so clearly illustrated). Triodes are cheaper to build than beam power tubes of a given size, simpler, and can be used for amplifiers of any size. Most 50 kW AM broadcast transmitters had two triodes in their modulators giving 30 kW audio power in Class B. The common 811 available under $20, though not an ideal tube, can give 200 easy watts for a pair. As can 211s, 845s, etc. The GEC book shows a 1 KW audio amp with a pair of largish glass triodes. Difficult to use? Just give them a filament supply of several amps, preferably from a filament transformer with shunts designed for that tube, a few kV on the plate and enough drive and they work fine. Audio is not only about power and characteristics on the paper, but about sound. Most if not all high power tubes are designed for high frequency transmitters, not for high-fidelity, and they will sound very poorly when used for an audio amp. I doubt this is correct. There are many examples where a tube can be used equally appropriately for RF or AF. The 211 makes a nice transmit tube and can be superlative as an audio tubes. 813 is another..... You will get a much better sound when using 4, 6 or 8 EL34 or 300B as only 2 more powerful tubes. Ain't necessarily so... Now, the controversy between pentode and triode is not new. If you look, most of the so called pentodes used in high fidelity audio are in fact beam-tetrodes. The main problem with the pentode is its high output impedance. The main problem with the triode is its low sensibility. Perhaps you mean sensitivity, or voltage gain. Its a very sensible choice for an output device.... The beam tetrode try to get most of the advantages of the triode as its relatively low output impedance and most of the advantages of the pentode as its high sensibility. And the result is a very good tube for power amplification. ??? But if you want to get a good result in audio with a beam tetrode, you must be very careful with the design. A triode design is easier because you don't have the g2. A good practice, if you are using a fixed g2 voltage, is to stabilize it. Just be doing it, the amp will archive at least a 2 time better dynamic at the output. But how many amps on the market are using a stabilized Vg2? The use of a slow time constant with RC filter used for g2 supply is all that is required for AB audio amps with multi grids because in fact the Eg2 variation at average power = 1/10 of clipping power is very small. Almost no one because it cost more money to build. I shunt regulate my screen supplies. A few 75V x 5 watt zener diodes and a power resistor of 10W is usually all that is needed. Another issue, and not only with the beam tetrode, is the quality of the tubes. Take the 6L6. It is hundred of different brands, but only a little part of those brands have a really good quality of manufacturing. It is in theory the same tube as a 807. Make an amp with 2 x 807, 600V DC on the middle of the output transformer when the amp is at full output, 300 V DC on the g2, and replace the 807 by 6L6 tubes. Most of them will just glow up at full output. And already at low level, they will arc inside the tube because of a too high Va, and this will sound like hell in the loudspeaker. Maybe depends which type of 6L6 one uses.... Take a preamp tube as the ECC83-12AX7. Buy a few tubes of different brands. You will get as many sound at the output as brands. In fact even more, because with the cheaper brands, different tubes will sound differently. So, when you want to compare tubes, you must not only say the type of the tubes, but the brand too. And when comparing tubes as different as a triode and a pentode, you must talk about the topology of the circuits. A good quality pentode will sound better as a poor quality triode. And a pentode used in a deign that have a good topology will sound better as a triode of the same quality but used in a circuit with a poor design. -- Dominique Michel Tubes brands do make different sound amoung the same type number and using pentodes in lieu of triodes ditto. Tubecraft involves many variables around simple ideas. Its all so much easier than class D DIY PWM amps.... Patrick Turner. |
#62
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Explanation still required for triode superiority
Phil wrote: Patrick Turner wrote: [snip] Professor child called the mutual effect of anode AND grid voltages in a triode a form of "self regulation". See Radio Engineering, by Terman, 1937. He does not call it NFB probably because it would have confused ppl at the time who were used to NFB ONLY being some external networking to get an amp of device to display lower Ra thd etc than otherwise it would without NFB. The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. When you have a 300B with Ia = 70mA, Ea = +400V, then if it acted like a resistor without NFB the R value would be 400 / 0.07 = 5,700 ohms. But where one maintains the grid bias voltage and fixes the cathode voltage, abd simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. One simply cannot deny that a huge anode feedback effect exists, and where you have a grid also able to control the Ia with a gm of about 5mA/V then there MUST be a summing of the anode and grid voltage effects according to some formula ( upon which Professor Child throws more light than I do ) . So its very easy to see that NFB is alive and operational in a triode. [snip] I am not a qualified university educated triodologist. But my powers of observation reveal NFB in triodes to me. But by exactly what process in purely technical terms would you use to allege NFB does NOT exist in triodes? Patrick, you're simply being stubborn at this point. We have pointed out, over and over, that a plate resistance, which, so far, you CANNOT and HAVE NOT proven does not exist, can account for all of the "feedback effects," by which you mean damping, that you talk about. The Ea / Ia at the quiecent state = 5,700 ohms for the 300B I mentioned. But why does it measure 800 ohms when small variations in Ea are made? if there was no FB and the tube was just a purely passive device like a resistor, the changes in Ea would give Ra = 5,700 ohms. but we get 800 ohms. How come? Yes, in the absence of tests which possibly can distinguish between anode resistance and triode feedback, we really don't know which it is. But to claim that feedback must exist *because* effects equivalent to either feedback or low plate resistance exist is unscientific. You have a choice, and that is why the rest of us simply state that, in the absence of any logical, intellectual, or engineering advantage for feedback, we prefer low plate resistance as a *model*. That's our choice. Maybe the other choice is better. But you have not given any analysis to my knowledge which proves that such a choice does not exist, or even that a feedback model is a better choice for audio or electronics. You call me stubborn, and refuse to proove I'm wrong, and you cannot deal with the idea of the mutual effect of the two changing voltages of grid and anode which BOTH have large effects on the Ia and so who is right? If say I am wrong, then so is Prfessor Child, and all the guys with better minds than yours or mine. Where is you alternative modelling? I see there is NFB in a triode not because I am stubborn, but because it hits me in the eye as being so very obvious, and its missing from all other devices. Patrick Turner. Phil |
#63
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Explanation still required for triode superiority
"Andre Jute" wrote in message oups.com...
Thanks for writing in, HP. I happen to agree with you, the model isn't real life. But it is the nearest we have to the vacuum inside the tube. I've already given this a good bash, and everyone else is bored with it. You can find my conclusions at http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm and http://members.lycos.co.uk/fiultra/K...dre%20Jute.htm But these conclusions are wrong, as I've already proved. The "Jute Triode Effect" is just your contrived name for "plate resistance", which physically is the result of moving electrons giving up their kinetic energy as heat when they smash into the plate. It has nothing to do with feedback. You're welcome to post it on your website, but it doesn't mean you are right. Sorry, that's just the way it is. If those you want as referees wish to come on RAT to give us the benefit of their wisdom, we should be delighted to welcome them (or welcome some of them back, as Steve for instance is an old RAT). Actually, it was a trick question. Steve Bench has already responded to my postings on this subject. I'll leave it to you to look it up and see what he had to say. Have a good one. -Henry |
#64
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Explanation still required for triode superiority
Henry Pasternack wrote: "Patrick Turner" wrote in message ... HP wrote: I've corrected the ID in my news client profile. Professor child called the mutual effect of anode AND grid voltages in a triode a form of "self regulation". See Radio Engineering, by Terman, 1937. I've read that book in the library, but don't have a copy of my own, so I can't really say for sure out of context what Terman meant by "self regulation". In the past, I've responded to this point by giving examples of systems that can be called "self-regulating", but where the regulation is the result of a dynamic equilibrium rather than negative feedback. The spinning electric motor and the falling parachute are two examples, but many others can be proposed. The self regulation is the combined net effect of the two active voltages in the triode, one is the anode voltage, the other the grid voltage, and the two electrostatic fields sum to give a net effect that governs Ia. I've also shown before how models of rate-limited systems, like the electric motor or even a plain resistor, can be refactored into equivalent negative feedback systems. But the feedback models don't add any information that we can't, in general, get from simpler models, and with much less effort. The same is true of triodes and feedback. Norton and Thevenin have the same predictive power as the feedback model, but are simpler and more useful. Please take note, I'm not arguing that the triode cannot be described in terms of negative feedback. What I am arguing is that this is a contrived and largely pointless complication. I am also showing how other models, both external and internal, can give us the same information about the tube without the need to invoke negative feedback. Finally, I am pointing out the inconsistencies, errors, and omissions in your own statements. The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. When you have a 300B with Ia = 70mA, Ea = +400V, then if it acted like a resistor without NFB the R value would be 400 / 0.07 = 5,700 ohms. But where one maintains the grid bias voltage and fixes the cathode voltage, abd simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. You get the exact same result if you represent the tube as an 800 Ohm resistor in series with a 344V battery, and no feedback is required. This is the Thevenin model. While your result is not inconsistent with feedback, the existence of an alternate model means your results cannot "prove" there is NFB in the triode. As I keep saying, any attempt to "prove" the existence of NFB in the tube by external observation is fallacious from the get-go. You should read and think about this carefully because it's a fundamental point. The triode indeed can be modelled as being equivalent to a super a low output impedance voltage generator whose output voltage is µ x Vg, and then Ra is added as a series resistor. This simple model of a triode does not include the NFB within the model, because there is no need to do so since the NFB is contained within the 3 terminals, and for modelling circuit gain the gene + Ra resistance is all one needs. One simply cannot deny that a huge anode feedback effect exists, and where you have a grid also able to control the Ia with a gm of about 5mA/V then there MUST be a summing of the anode and grid voltage effects according to some formula ( upon which Professor Child throws more light than I do ) . So its very easy to see that NFB is alive and operational in a triode. But I certainly can deny it. I hope you'll agree the mechanism at work here is the same even if we impose the condition of linearity. And if this is true, then by the principle of superposition we can separate out the effects of the control grid and the plate and analyze them separately. The control grid, clearly, is analgous to the non-inverting input on the op-amp. It's in the forward path, so we can ignore it. In fact, we can tie the control grid to the cathode, or remove it entirely, and the analysis stays the same. And this takes us back to the diode argument and your inconsistent interpretation of plate resistance. The grid isn't the non inverting input; the cathode is. Anyway, the real analogy of a triode to an opamp is one where the opamp has a high impedance shunt FB between the output and input terminal and the actual connection to the opamp has a small signal. So such an opamp may have open loop gain = 100,000 at 500Hz, and have a 1M output to actual opamp live inverting input connection, and say a 10k R between this input which is called the virtual earth input, and the input to the amp as a whole including the FB loopP If +10V appears at the opamp output, then -0.001 V is at the actual virtual earth input, and current is 10V / 1,000k across the 1M, = 0.01mA. So voltage across the 10k input resistance = 0.01 x 10 = 0.1V, so amp input terminal signal = -0.101V, or about 1/100 of the output signal because the ratio of FB resistors are 1:100. In the triode the two arms of the shunt FB network are not resistances but are elctrostatic fields which sum to form a virtual earth, or internal control point which is a much lower voltage than the actual voltage applied to the grid which is the input terminal of the amp at the front end of the shunt NFB network. Your observation about the summing of the effects of the control grid and the plate is really the crux of your argument because it's the only statement you've ever made to justify that negative feedback occurs. But the argument can't be valid, as I've shown, because it fails to acknowledge the principle of superposition. Superposition says that the summing is irrelevant because the effects of the grid and the plate can be treated separately. This is why the point about the diode is so important. But no grid exists in a diode. Summing of bother grid and anode actually occurs; its not something I suppose occurs, it really does occur. Thee triode cannot be considered without its NFB unless one makes a mental model of a perfect pentode with NFB. This isn't true at all, and is a perfect example of "begging the question", or taking the conclusion of an argument as one of its premises. We are trying to evaluate the claim that triodes have internal negative feedback. Declaring, a priori, that a pentode is a triode with negative feedback removed, and showing that adding feedback to the pentode transforms it into a triode begs the question since it depends on the presumption that the triode had negative feedback in the first place. I see the triode as being like a pentode but one with a resistance shunt NFB arrangement added to it. There is a strong resemblance and in fact we can get a pentode to act almost exactly like a triode with such a two resistance shunt NFB in terms of Rout, THD, bw etc. If one takes a 6AU6 one cann perform the experiment easily. But the pentode with the two R shunt NFB is very different because the input resistance is set by R1. In a triode, the input arm of the shunt NFB network is not a resistance but is a high impedance voltage field. Same with the anode field; it has very high impedance as well, but the two fields act effectively together to give a net field effect on the flow of electrons from the space charge gathered around the cathode. The simple, non-feedback explanation for triode behavior is as follows. The plate voltage establishes an electric field, and therefore a potential gradient, at the surface of the cathode that draws electrons out of the cathode and sweeps them toward the plate. The electrons are rapidly emitted into the vicinity of the cathode until the potential gradient, by Poisson's equation, reaches zero. At this point, the net rate of electron emission from the cathode equals the rate at which electrons are swept to the plate and the plate current settles into a steady equilibrium. Increasing or decreasing the plate voltage throws the system out of equilibrium and the plate current varies upward or downward until the equilibrium is reestablished at a new operating point. This is about right; cathode emission can be many times Ia, but a state of equilibrium exists as a result of the combined action of anode and grid voltages in the vicinity Because there are TWO such opposing fields that control Ia, a shunt NFB network exists. You can call this negative feedback if you want and you won't be incorrect. Well that's all I ask people to believe. But in doing so, you should be prepared to accept that many, many other natural systems are also examples of negative feedback, not the least of which is the lowly vacuum diode. You also won't be excluding interpretations that do not depend on the presumption of feedback. If there is MORE than one controlling field, NFB exists, but where there is only ONE field, such as in a diode, then there is no NFB and the device acts as a rather non linear resistance. [Pentode coments deleted] Irrelevant. I am not a qualified university educated triodologist. True. I would never say that someone needs a university degree to learn to build audio gear. You are a perfect case in point, Patrick, how someone without a Triodology degree can become an accomplished tube technician and a prolific designer. But you need to understand, no matter how broad your practical experience may be, that there are limits to your conceptual knowledge. For instance, your example with the 300B above tells me you are confused about the difference between small-signal and large-signal circuit analysis. This isn't a minor error, either. It's a giant, sucking hole in your argument. I suggest you visit my educational pages at my website. There are models of tubes as imaginery voltage amps with series R for Ra, and NFB is explained as I have here. But my powers of observation reveal NFB in triodes to me. Yes, and to a fundamentalist Christian, the diversity of species reveals the wonder and glory of creation and thereby proves the existence of God. But that doesn't qualify him to be a biologist (much as he may think so). But by exactly what process in purely technical terms would you use to allege NFB does NOT exist in triodes? I believe I've answered that question many times over the past few days. I can't help you if you didn't understand. I have a rule I call the "Law of Conservation of Complexity". It says for any given topic there is a lower bound to how simple a valid explanation can be. If the audience lacks the sophistication to follow along at that level, than no explanation, no matter how correct and clear, will ever make sense to that audience. Have ye not just mentioned that the triode is like a battery with Ra in series? That is true what you say, but doesn't disprove NFB, which I say exists despite the triode being able to be modelled as the battery + R, or low Z generator + R. The above list may not wish to join our little discussions because the morons and arsoles wait impatiently with buckets of **** to drench any attempts of true intellectual discourse and democracy. On that point, you won't get any disagreement from me. Although we might not see eye-to-eye when it comes to assigning blame to specific individuals. Meanwhile, we merely need Ra, µ and gm values from the data sheets to design good amps, and some Ra curves are also handy for various Eg values. The data and curves are derived from the triode with its natural NFB in place IMHO, and the amp maker does not need to know what the open loop characteristic gain of the triode would be if it had its anode to space charge NFB arm completely and perfectly screened off from having any effect. Even in a pentode, there is a finite value for Ra; some small amount anode NFB still is in effect The NFB is dramatically reduced by the screen. One could use the screen to give a pentode almost infinite Ra by applying a slightly positive FB signal to the screen. The Ra could even be made into a negative resistance. But such fiddles are all done with external loopings; none a doable with natural electrode connections. As long as we are discussing the issues peacefully, then all is well. I'l agree to disagree at the finish without rancour and let others decide what they see as being true. Patrick Turner. -Henry |
#65
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Patrick Turner wrote:
Phil wrote: Patrick Turner wrote: [snip] Professor child called the mutual effect of anode AND grid voltages in a triode a form of "self regulation". See Radio Engineering, by Terman, 1937. He does not call it NFB probably because it would have confused ppl at the time who were used to NFB ONLY being some external networking to get an amp of device to display lower Ra thd etc than otherwise it would without NFB. The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. When you have a 300B with Ia = 70mA, Ea = +400V, then if it acted like a resistor without NFB the R value would be 400 / 0.07 = 5,700 ohms. But where one maintains the grid bias voltage and fixes the cathode voltage, abd simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. One simply cannot deny that a huge anode feedback effect exists, and where you have a grid also able to control the Ia with a gm of about 5mA/V then there MUST be a summing of the anode and grid voltage effects according to some formula ( upon which Professor Child throws more light than I do ) . So its very easy to see that NFB is alive and operational in a triode. [snip] I am not a qualified university educated triodologist. But my powers of observation reveal NFB in triodes to me. But by exactly what process in purely technical terms would you use to allege NFB does NOT exist in triodes? Patrick, you're simply being stubborn at this point. We have pointed out, over and over, that a plate resistance, which, so far, you CANNOT and HAVE NOT proven does not exist, can account for all of the "feedback effects," by which you mean damping, that you talk about. The Ea / Ia at the quiecent state = 5,700 ohms for the 300B I mentioned. But why does it measure 800 ohms when small variations in Ea are made? Because the *model* of a triode includes a voltage offset in series with a diode, caused by the grid. Given, say, -10 Vg, you will get no positive current until you reach a certain plate voltage, enough to overcome the voltage offset caused by the grid. Specifically, the grid can repel the electrons until the plate voltage more or less equals the grid voltage times mu. You get no negative current because a triode only conducts one way, like a diode. Similarly, if you have two resistors in series, with a battery between them, you get no positive current when placing a voltage after the second resistor until its voltage equals the battery placed between the two resistors. A triode acts like a resistor with a voltage offset which is controlled by the grid. if there was no FB and the tube was just a purely passive device like a resistor, the changes in Ea would give Ra = 5,700 ohms. but we get 800 ohms. How come? See above. Yes, in the absence of tests which possibly can distinguish between anode resistance and triode feedback, we really don't know which it is. But to claim that feedback must exist *because* effects equivalent to either feedback or low plate resistance exist is unscientific. You have a choice, and that is why the rest of us simply state that, in the absence of any logical, intellectual, or engineering advantage for feedback, we prefer low plate resistance as a *model*. That's our choice. Maybe the other choice is better. But you have not given any analysis to my knowledge which proves that such a choice does not exist, or even that a feedback model is a better choice for audio or electronics. You call me stubborn, and refuse to proove I'm wrong, and you cannot deal with the idea of the mutual effect of the two changing voltages of grid and anode which BOTH have large effects on the Ia and so who is right? If say I am wrong, then so is Prfessor Child, and all the guys with better minds than yours or mine. I call you stubborn because you claim that feedback exists, when an alternative model explains everything (admittedly, as far I know) just as well. To say that it *might* be feedback would be okay, but until you have proofs or experiments that rule out the resistor model, you cannot say definitively that triodes have feedback. The plate may simply pull electrons along in exactly the same manner as a battery pulls electrons through an ordinary resistor. Then again, perhaps it would be *best* described as feedback, and I can easily admit that. However, Henry has some very convincing lines of reasoning that show no advantage or greater accuracy or anything like that for feedback, I have not been able to find lines of reasoning to contradict him, and again, as far as I know, neither have you! I don't have to prove that triodes do not have feedback to "prove you wrong," when all I am trying to claim is that you are not necessarily right! Let me see if I can make this clear. Let's assume, for a moment, that a test will appear that truly can distinguish between low impedances caused by feedback, and low impedances caused by a low impedance, a simple resistance. I do not know for certain what that test would tell us about triodes. As far as I can tell, neither do you. THAT appears to me to be the honest answer! Since resistor models are less complicated than feedback models, I understandably believe that everyone should use the simpler model until it is proven to be a less accurate description, since humans make fewer errors when using simpler, but equally powerful, models. The MOMENT someone proves that feedback is the more accurate model, I will state, publicly, that you were right, and that unless we are working in some situation where there is no significant difference between the two models, we should use feedback to describe triodes. But not until then! And honestly, Patrick, do you not agree that if triodes have feedback, then so do resistors? Batteries affect the electric field surrounding the atoms in resistors, and increasing the voltage increases the field strength, just as it does in triodes and diodes, and if it weren't for that, the resistance would be much higher, perhaps infinite. Mind you, resistors might indeed have feedback, but until we find situations that require us to view them in such a manner, why on Earth would we want to replace the much simpler resistor model for resistors with a feedback model? And the same question applies to triodes and diodes. Where is you alternative modelling? We have stated it over and over and over again -- well, we've stated the resistor part, perhaps the battery part was not stated as clearly as it should have been -- I don't know how many times we are supposed to repeat ourselves. I see there is NFB in a triode not because I am stubborn, but because it hits me in the eye as being so very obvious, and its missing from all other devices. Yes, it appears to be feedback to you. It appears to be a resistance in series with a voltage to everyone else. Who is right? Until we have better proofs than anyone has presented, on either side, that "the other side's model" cannot fully account for a triode's behavior, we do not know which one is truly correct, and therefore should use the simpler model, and that is the resistance model. Phil Patrick Turner. Phil |
#66
Posted to rec.audio.tubes
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Explanation still required for triode superiority
"Patrick Turner" wrote in message ...
[Yada, yada, yada] Whatever. I've wasted enough of my time on you, Patrick. -Henry |
#67
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Phil wrote: Patrick Turner wrote: Phil wrote: Patrick Turner wrote: [snip] Professor child called the mutual effect of anode AND grid voltages in a triode a form of "self regulation". See Radio Engineering, by Terman, 1937. He does not call it NFB probably because it would have confused ppl at the time who were used to NFB ONLY being some external networking to get an amp of device to display lower Ra thd etc than otherwise it would without NFB. The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. When you have a 300B with Ia = 70mA, Ea = +400V, then if it acted like a resistor without NFB the R value would be 400 / 0.07 = 5,700 ohms. But where one maintains the grid bias voltage and fixes the cathode voltage, abd simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. One simply cannot deny that a huge anode feedback effect exists, and where you have a grid also able to control the Ia with a gm of about 5mA/V then there MUST be a summing of the anode and grid voltage effects according to some formula ( upon which Professor Child throws more light than I do ) . So its very easy to see that NFB is alive and operational in a triode. [snip] I am not a qualified university educated triodologist. But my powers of observation reveal NFB in triodes to me. But by exactly what process in purely technical terms would you use to allege NFB does NOT exist in triodes? Patrick, you're simply being stubborn at this point. We have pointed out, over and over, that a plate resistance, which, so far, you CANNOT and HAVE NOT proven does not exist, can account for all of the "feedback effects," by which you mean damping, that you talk about. The Ea / Ia at the quiecent state = 5,700 ohms for the 300B I mentioned. But why does it measure 800 ohms when small variations in Ea are made? Because the *model* of a triode includes a voltage offset in series with a diode, caused by the grid. Given, say, -10 Vg, you will get no positive current until you reach a certain plate voltage, enough to overcome the voltage offset caused by the grid. Specifically, the grid can repel the electrons until the plate voltage more or less equals the grid voltage times mu. You get no negative current because a triode only conducts one way, like a diode. Similarly, if you have two resistors in series, with a battery between them, you get no positive current when placing a voltage after the second resistor until its voltage equals the battery placed between the two resistors. A triode acts like a resistor with a voltage offset which is controlled by the grid. All you are doing like nearly everyone else is denying the summing NFB interactive effects of anode voltage AND grid voltage upon Ia, and saying the triode is merely a model of a battery or low Z voltage gene in series with a diode or resistor which is equivalent to Ra. A triode becomes like a diode when its grid is tied to the cathode or at a fixed voltage in reference to the cathode; then there is no Vg-k variation, and no FB either, because TWO voltage changes are required to make the loop for FB to occur. We already know all the triode models are true, but true because of the NFB. In a pentode there is also a battery or low Z voltage gene producing µ x Eg and with an R in series which is equivalent to Ra. In a pentode, µ = gm x Ra and without the NFB, and for a 6AU6 µ approx = 0.0045A/V x 1,500,000 ohms = 6,750 at 7.6mA. We can IMAGINE that the 6AU6 is a voltage gene with an output of 6,6750V for 1V input from a grid, and then we have Ra as a series R = 1.5M and say we have a load of 20k then the current in the Ra + 20k is 6,750V / ( 1.5M + 20k ) = 4.44mA and so the load voltage = 20 x 4.44 = 89V. Thus the tube has a gain of 89. If the load is altered and voltage readings taken then one can deduce Ra = 1.5M If the anode voltage is altered by a low Z voltage source we find Ra = 1.5M although Ea / Ia = 200V / 0.0076A = 26.3k, so how come we measure the Ra at 1.5M? Its because there is VIRTUALLY NO NFB, the opposite case to a triode. If we connect the screen to anode, and triodise the 6AU6, then the anode voltage is allowed to affect the Ia and the apparent Ra drops because the µ drops from 6,750 to 36 due to NFB and the Ra = µ / gm = 36 / 0.0048 = 7,500ohms, so the NFB has a large effect on reducing Ra. What other mechanism do you suggest causes Ra to be so reduced? Then we should consider the case of a triode where there is NO ANODE CURRENT CHANGE IN THE OPERATION. This is where there is a CCS load, and no anode current occurs. The summed effect of the grid and anode voltage upon the space charge remains. NO anode current change is possible because of the infinite resistance of the load. The NFB effect is maximal and voltage gain = triode µ. Witha 6AU6 pentode with CCS, the µ = gain and would be 6,750 because there is a very small VOLTAGE caused NFB effect. How does one explain the tube working with CCS load without thinking of the amounts of local NFB???? if there was no FB and the tube was just a purely passive device like a resistor, the changes in Ea would give Ra = 5,700 ohms. but we get 800 ohms. How come? See above. You don't explain it. Yes, in the absence of tests which possibly can distinguish between anode resistance and triode feedback, we really don't know which it is. But to claim that feedback must exist *because* effects equivalent to either feedback or low plate resistance exist is unscientific. You have a choice, and that is why the rest of us simply state that, in the absence of any logical, intellectual, or engineering advantage for feedback, we prefer low plate resistance as a *model*. That's our choice. Maybe the other choice is better. But you have not given any analysis to my knowledge which proves that such a choice does not exist, or even that a feedback model is a better choice for audio or electronics. You call me stubborn, and refuse to proove I'm wrong, and you cannot deal with the idea of the mutual effect of the two changing voltages of grid and anode which BOTH have large effects on the Ia and so who is right? If say I am wrong, then so is Prfessor Child, and all the guys with better minds than yours or mine. I call you stubborn because you claim that feedback exists, when an alternative model explains everything (admittedly, as far I know) just as well. I won't call you stubborn. The "alternative models" of a triode have been known by many for 70 years and are explained at my website and we agree on the models of battery/voltage gene with series R to represent Ra. But you still fail to see the NFB that exists. The models of generator + Ra resistance DO NOT explain or even include the NFB effects, but are the models of the tube working AFTER TAKING INTO ACCOUNT WHATEVER NFB EXISTS. To say that it *might* be feedback would be okay, but until you have proofs or experiments that rule out the resistor model, you cannot say definitively that triodes have feedback. I leave you to consider that minds better than yours have concluded there is NFB within a triode. The plate may simply pull electrons along in exactly the same manner as a battery pulls electrons through an ordinary resistor. No such pull along effect occurs in resistors. A resistor works in an entirely different manner to any tube. Then again, perhaps it would be *best* described as feedback, and I can easily admit that. The NFB is only evident when one considers the COMBINED NET EFFECT OF TWO VOLTAGES within the tube, ie, grid and anode voltages. However, Henry has some very convincing lines of reasoning that show no advantage or greater accuracy or anything like that for feedback, I have not been able to find lines of reasoning to contradict him, and again, as far as I know, neither have you! I don't have to prove that triodes do not have feedback to "prove you wrong," when all I am trying to claim is that you are not necessarily right! Try reading a few more books about triodes rather than seeking some NFB de-bunking premise from Henry. With all due respsect to Henry, he ain't the world's authority on vacuum tube theory. Nor am I. So read up elsewhere. Until you have read a lot more, consider yourself ignorant, because that would be a fact. Let me see if I can make this clear. Let's assume, for a moment, that a test will appear that truly can distinguish between low impedances caused by feedback, and low impedances caused by a low impedance, a simple resistance. Resistances can be any value, and characterized by being a fixed value for a large range of currents and frequencies. I do not know for certain what that test would tell us about triodes. As far as I can tell, neither do you. Well you are not able to hear or see what I have been saying. You don't want to accept you are mostv likely to be wrong, and ignorant. You have read almost nothing, have not benefitted from education, and are at a similar position of where you might think you know your stomach's anatomy by gazing at your navel. THAT appears to me to be the honest answer! Since resistor models are less complicated than feedback models, I understandably believe that everyone should use the simpler model until it is proven to be a less accurate description, since humans make fewer errors when using simpler, but equally powerful, models. The simple models INCLUDES THE NFB AND USES VALUES FOR RA which exist because of the NFB. The models DON'T EXPLAIN OR INCLUDE THE NFB MODELS. The models were invented TO BE A SIMPLIFIED TOOL for design purposes. The MOMENT someone proves that feedback is the more accurate model, I will state, publicly, that you were right, and that unless we are working in some situation where there is no significant difference between the two models, we should use feedback to describe triodes. But not until then! And honestly, Patrick, do you not agree that if triodes have feedback, then so do resistors? Resistors have no NFB in the same way pigs don't have wings and cannot fly. Triodes do have NFB because there is an interactive voltage summing of two electrodes which act upon the space charge. I ask you to consider not making yourself look any more ignorant than you appear to be by likening resistors to vacuum tubes in any way. Batteries affect the electric field surrounding the atoms in resistors, and increasing the voltage increases the field strength, just as it does in triodes and diodes, and if it weren't for that, the resistance would be much higher, perhaps infinite. Huh? This is a weird statement and I suggest you consult a professor of electronics to guide you arrange words with more meaning. maybe he'll give you a reading list if you decide to attend his classes at a university. The exams they set at the end of such courses exist to guage whether or not you understand what was in the books you may have read. Mind you, resistors might indeed have feedback, but until we find situations that require us to view them in such a manner, why on Earth would we want to replace the much simpler resistor model for resistors with a feedback model? And the same question applies to triodes and diodes. I suggest you don't know if there is or isn't NFB in resistances. Find out for sure, will you, and let us know what you think and why. You need to know, to understand. Where is you alternative modelling? We have stated it over and over and over again -- well, we've stated the resistor part, perhaps the battery part was not stated as clearly as it should have been -- I don't know how many times we are supposed to repeat ourselves. We agree on the models, but the models includes the NFB in operation. The NFB loop elements are not included in the model because they were designed to allow simple circuit analysis. The triode model is low µ generator and low Ra series resistance, lots of local NFB. The pentode model has high µ gene and high Ra series R, and very little NFB. The model of a vacuum tube as a battery with series R is only correct for DC operartion and is severly limited in its usefulness in applications and the AC model with the battery being replaced with a generator of low Z output resistance whose output = µ x Vg is the accurate model and useful for both DC and AC operation. Unless you understand the operation of the vacuum tube as AC generator with series R for Ra, or else constant current generator = gm x Vg shunted by resistance = Ra then your mind is severly limited for any exercize involving making up circuitry where the current flows can be very basically examined. I see there is NFB in a triode not because I am stubborn, but because it hits me in the eye as being so very obvious, and its missing from all other devices. Yes, it appears to be feedback to you. It appears to be a resistance in series with a voltage to everyone else. There are many more ppl than myself who believe in the NFB withing vacuum tubes. The model of resistance in series with battery or low Z voltage gene has been known for 70 years as a basic tool, and includes the effects of whatever NFB exists. Because you cannot see the NFB, you say it cannot exist. I say that not only is there NFB within vacuum tubes, but also that you are ignorant, and in need of a serious increase in your education and you must forthwith proceed without delay to a nice large pile of books wherin you may find answers you are not getting from me. Until you have read the books, and proved you understand what you have read, you remain someone who is guessing his way through life, unguided by any real knowledge. Patrick Turner. Who is right? Until we have better proofs than anyone has presented, on either side, that "the other side's model" cannot fully account for a triode's behavior, we do not know which one is truly correct, and therefore should use the simpler model, and that is the resistance model. Phil Patrick Turner. Phil |
#68
Posted to rec.audio.tubes
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Explanation still required for triode superiority
"Patrick Turner" wrote in message ...
A triode becomes like a diode when its grid is tied to the cathode or at a fixed voltage in reference to the cathode; then there is no Vg-k variation, and no FB either, because TWO voltage changes are required to make the loop for FB to occur. Three days ago, you wrote: The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. But where one maintains the grid bias voltage and fixes the cathode voltage, and simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. Hah. Gotcha there. -Henry |
#69
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Patrick Turner wrote:
Phil wrote: Patrick Turner wrote: Phil wrote: Patrick Turner wrote: [snip] Professor child called the mutual effect of anode AND grid voltages in a triode a form of "self regulation". See Radio Engineering, by Terman, 1937. He does not call it NFB probably because it would have confused ppl at the time who were used to NFB ONLY being some external networking to get an amp of device to display lower Ra thd etc than otherwise it would without NFB. The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. When you have a 300B with Ia = 70mA, Ea = +400V, then if it acted like a resistor without NFB the R value would be 400 / 0.07 = 5,700 ohms. But where one maintains the grid bias voltage and fixes the cathode voltage, abd simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. One simply cannot deny that a huge anode feedback effect exists, and where you have a grid also able to control the Ia with a gm of about 5mA/V then there MUST be a summing of the anode and grid voltage effects according to some formula ( upon which Professor Child throws more light than I do ) . So its very easy to see that NFB is alive and operational in a triode. [snip] I am not a qualified university educated triodologist. But my powers of observation reveal NFB in triodes to me. But by exactly what process in purely technical terms would you use to allege NFB does NOT exist in triodes? Patrick, you're simply being stubborn at this point. We have pointed out, over and over, that a plate resistance, which, so far, you CANNOT and HAVE NOT proven does not exist, can account for all of the "feedback effects," by which you mean damping, that you talk about. The Ea / Ia at the quiecent state = 5,700 ohms for the 300B I mentioned. But why does it measure 800 ohms when small variations in Ea are made? Because the *model* of a triode includes a voltage offset in series with a diode, caused by the grid. Given, say, -10 Vg, you will get no positive current until you reach a certain plate voltage, enough to overcome the voltage offset caused by the grid. Specifically, the grid can repel the electrons until the plate voltage more or less equals the grid voltage times mu. You get no negative current because a triode only conducts one way, like a diode. Similarly, if you have two resistors in series, with a battery between them, you get no positive current when placing a voltage after the second resistor until its voltage equals the battery placed between the two resistors. A triode acts like a resistor with a voltage offset which is controlled by the grid. All you are doing like nearly everyone else is denying the summing NFB interactive effects of anode voltage AND grid voltage upon Ia, and saying the triode is merely a model of a battery or low Z voltage gene in series with a diode or resistor which is equivalent to Ra. Oh for god's sake WOULD YOU WAKE UP!!! For the umpteenth time, the fact that some theory fits the known facts regarding the dinosaur's demise DOES NOT MAKE THAT THEORY TRUE! Patrick, no one is denying that you could have a summing effect from plate and grid voltages, and I'm getting tired of you telling me "you don't believe X" when I have told you, over and over, that I have no evidence that X isn't true. For the umpteenth time, the fact that your feedback theory can explain things does not, and will not ever, BY ITSELF prove that it is true! Why is this so difficult for you to understand? What references or experiments did you perform that PROVED that increasing the voltage across a triode does not simply pull more electrons past all the obstacles in a triode, in exactly the same way that increasing the voltage across a resistor pulls more electrons past the thermally agitated atoms? When did you PROVE that a simple resistance mechanism does NOT exist in a triode? Did you never prove that? Then you cannot rule it out as a possible explanation, period. Basic reasoning 101. Duh. And please, please don't try to tell me that because your theory fits, therefore all other theories are "proven" wrong (see dinosaur example above). A triode becomes like a diode when its grid is tied to the cathode or at a fixed voltage in reference to the cathode; then there is no Vg-k variation, and no FB either, because TWO voltage changes are required to make the loop for FB to occur. What??? You know, up to now, I've thought your feedback model had real merit, and I also thought you straightened out your thoughts on the diode/triode issues, so let's get this straight. If I tie the grid to the cathode, and increase the voltage across the tube, I soon get a current of 100 mA and a dynamic resistance of, say, 600 ohms. But there's no feedback here, according to you. If I tie the grid at -50 Vg, and repeat until I reach 100 mA, I again find a dynamic resistance of 600 ohms. And again, according to you, there's no feedback??? But now, if I put in an audio signal, but measure the dynamic resistance, I find that it's 600 ohms, again, at around 100 mA, but NOW there's feedback??? Patrick, the whole point about the difference between triodes and pentodes or transistors is that, given a *fixed* grid voltage, changing the voltage across the tube causes a large change in current. It has a low output resistance. When the speaker tries to change its voltage due to stored energy, the triode resists this, even if the grid voltage happens to be constant at that time. Now, you can say that the change in plate voltage changes the flow of electrons to the plate in the SAME WAY as changing the grid voltage, which would be a feedback model. Or, you can say that a triode fails to isolate a basic resistance mechanism which exists in triodes and pentodes -- where increasing the plate or screen voltage draws more current through the spaces between the grid wires, just as increasing the voltage across a resistor draws more current through the atoms -- from the plate voltage. In other words, the screen *isolates* the inherent resistance from changes in plate voltage, which would be a resistance model. So far, so good, but if you think your feedback model requires feedback to "mystically" disappear every time the grid voltage happens to be held steady, then you need to abandon your feedback model, because that's clearly stupid. Mind you, *I* won't abandon your feedback model, because I know that it does apply to diodes, resistors, and triodes with constant grid voltages, and I can accept that. But then, neither do I assume that such a weird model is true merely because it, like other models, happens to fit the facts. We already know all the triode models are true, but true because of the NFB. A claim, backed up by nothing but faulty arguments (meaning you have no proof). In a pentode there is also a battery or low Z voltage gene producing µ x Eg and with an R in series which is equivalent to Ra. In a pentode, µ = gm x Ra and without the NFB, and for a 6AU6 µ approx = 0.0045A/V x 1,500,000 ohms = 6,750 at 7.6mA. We can IMAGINE that the 6AU6 is a voltage gene with an output of 6,6750V for 1V input from a grid, and then we have Ra as a series R = 1.5M and say we have a load of 20k then the current in the Ra + 20k is 6,750V / ( 1.5M + 20k ) = 4.44mA and so the load voltage = 20 x 4.44 = 89V. Thus the tube has a gain of 89. If the load is altered and voltage readings taken then one can deduce Ra = 1.5M If the anode voltage is altered by a low Z voltage source we find Ra = 1.5M although Ea / Ia = 200V / 0.0076A = 26.3k, so how come we measure the Ra at 1.5M? Its because there is VIRTUALLY NO NFB, the opposite case to a triode. Or because the pentode shields its inherent low resistance -- and if you change the screen voltage, you will quickly see that such a low resistance exists -- from changes in plate voltage. Reasoning 101, the presence of one possible explanation DOES NOT PRECLUDE other possible explanations. The existence of the phlogiston theory of combustion did not prove that the Lavosier's oxygen theory of combustion was false. If we connect the screen to anode, and triodise the 6AU6, then the anode voltage is allowed to affect the Ia and the apparent Ra drops because the µ drops from 6,750 to 36 due to NFB OR because you are no longer shielding the low resistance from changes in plate voltage. Tell me again, what does the NFB model achieve that the low resistance model does not? and the Ra = µ / gm = 36 / 0.0048 = 7,500ohms, so the NFB has a large effect on reducing Ra. What other mechanism do you suggest causes Ra to be so reduced? The existence of a shield/screen that prevents changes in plate voltage from accessing the low internal resistance, just as we have said (in so many words) all along. Then we should consider the case of a triode where there is NO ANODE CURRENT CHANGE IN THE OPERATION. Okay, I'll bite. Who knows? Maybe you'll actually prove that NFB is indeed the preferred explanation. This is where there is a CCS load, and no anode current occurs. No changes in plate current. Got it. The summed effect of the grid and anode voltage upon the space charge remains. So? In other words, we can continue to view this situation using the NFB model. Fine, that means that it has not so far been proven false. That fact tells us NOTHING about the resistance model. NO anode current change is possible because of the infinite resistance of the load. True. The NFB effect is maximal and voltage gain = triode µ. Whatever (but Av = u, true). Witha 6AU6 pentode with CCS, the µ = gain and would be 6,750 because there is a very small VOLTAGE caused NFB effect. Or, the resistance is not completely shielded from the plate voltage, preventing u from being infinite. True. How does one explain the tube working with CCS load without thinking of the amounts of local NFB???? What's your point? In both cases, the grid-cathode voltage MUST change if you are to change the plate-cathode voltage, although you need to change it less with a pentode. So? With an unshielded resistance, the grid-cathode voltage must change more to compensate for that unshielded resistance. So? That's just another viewpoint of the same low plate resistance of a triode. if there was no FB and the tube was just a purely passive device like a resistor, the changes in Ea would give Ra = 5,700 ohms. but we get 800 ohms. How come? See above. You don't explain it. I did explain it, you merely didn't understand it (which might not be your fault). The voltage in series with a resistance model means that you get no current at all until Vp is approximately mu x Vg, at which point the 800 ohm resistance comes into play. That's the model, and it correctly describes triode behavior. Yes, in the absence of tests which possibly can distinguish between anode resistance and triode feedback, we really don't know which it is. But to claim that feedback must exist *because* effects equivalent to either feedback or low plate resistance exist is unscientific. You have a choice, and that is why the rest of us simply state that, in the absence of any logical, intellectual, or engineering advantage for feedback, we prefer low plate resistance as a *model*. That's our choice. Maybe the other choice is better. But you have not given any analysis to my knowledge which proves that such a choice does not exist, or even that a feedback model is a better choice for audio or electronics. You call me stubborn, and refuse to proove I'm wrong, and you cannot deal with the idea of the mutual effect of the two changing voltages of grid and anode which BOTH have large effects on the Ia and so who is right? If say I am wrong, then so is Prfessor Child, and all the guys with better minds than yours or mine. I call you stubborn because you claim that feedback exists, when an alternative model explains everything (admittedly, as far I know) just as well. I won't call you stubborn. The "alternative models" of a triode have been known by many for 70 years and are explained at my website and we agree on the models of battery/voltage gene with series R to represent Ra. But you still fail to see the NFB that exists. Be fair and accurate here; I still fail to see a PROOF that NFB correctly describes a triode, while resistance (plus a voltage) does not. The models of generator + Ra resistance DO NOT explain or even include the NFB effects, but are the models of the tube working AFTER TAKING INTO ACCOUNT WHATEVER NFB EXISTS. I have no idea what your point is here. To say that it *might* be feedback would be okay, but until you have proofs or experiments that rule out the resistor model, you cannot say definitively that triodes have feedback. I leave you to consider that minds better than yours have concluded there is NFB within a triode. That is merely an argument, an indication method, not a proof. By the way, which better minds are you thinking of? The plate may simply pull electrons along in exactly the same manner as a battery pulls electrons through an ordinary resistor. No such pull along effect occurs in resistors. Oh really? Pray tell how a resistor does work. A resistor works in an entirely different manner to any tube. Which would be ... Then again, perhaps it would be *best* described as feedback, and I can easily admit that. The NFB is only evident when one considers the COMBINED NET EFFECT OF TWO VOLTAGES within the tube, ie, grid and anode voltages. Ridiculous, the low impedance of a triode is quite intact when the grid voltage is fixed. Furthermore, simply remove the grid from a triode (there are several rectifiers where this was done), and I guarantee that the dynamic resistance for a given plate voltage will be about the same as in the triode version when the grid is tied to ground, and yet you're claiming that the diode version does not have feedback, and therefore should have a much higher resistance. Select equal current levels for the diode version and the triode version using several fixed values for the grid voltage, and you still get equal dynamic resistances. Put an audio signal in, and measure the dynamic resistance at some moment in time, you will still get the same values for a given current level. If a triode has feedback, then a diode has feedback. That is NOT enough to make me abandon the NFB model -- although it gave me pause for a while -- why should you feel it's necessary to DENY that a diode has the same feedback mechanism you claim exists for triodes? However, Henry has some very convincing lines of reasoning that show no advantage or greater accuracy or anything like that for feedback, I have not been able to find lines of reasoning to contradict him, and again, as far as I know, neither have you! I don't have to prove that triodes do not have feedback to "prove you wrong," when all I am trying to claim is that you are not necessarily right! Try reading a few more books about triodes rather than seeking some NFB de-bunking premise from Henry. With all due respsect to Henry, he ain't the world's authority on vacuum tube theory. He could be the devil himself, but that's irrelevant, along with his knowledge, when it comes to the quality of his arguments on this matter. You don't "disprove" a theory by saying the author is stupid or evil. You ignore the characteristics of the author altogether, and focus on the accuracy, or lack thereof, of the theory itself. Reasoning 101. Nor am I. So read up elsewhere. Until you have read a lot more, consider yourself ignorant, because that would be a fact. A general criticism without any support or examples. An old debating trick. Useless ... Let me see if I can make this clear. Let's assume, for a moment, that a test will appear that truly can distinguish between low impedances caused by feedback, and low impedances caused by a low impedance, a simple resistance. Resistances can be any value, and characterized by being a fixed value for a large range of currents and frequencies. The point was to assume, to hypothesize, that a test capable of distinguishing between a NFB model and a resistance model exists. Given that hypothesis ... I do not know for certain what that test would tell us about triodes. As far as I can tell, neither do you. Well you are not able to hear or see what I have been saying. That would indeed be one explanation. Another would be just the reverse, that you insist on ignoring the fact that without a proof that one model is correct, and the other model incorrect, you cannot justifiably claim that the low output impedance of triodes is definitely due to a feedback mechanism. You don't want to accept you are mostv likely to be wrong, and ignorant. That put-down doesn't necessarily follow from facts; it's just another unsupported criticism, and therefore useless. You have read almost nothing, have not benefitted from education, and are at a similar position of where you might think you know your stomach's anatomy by gazing at your navel. **** you, Patrick. You know, every once in a while I think that Ian is right; you're a bully. Or at the very least, you act like one. Let me get this straight. I'm just a stupid **** because I don't believe you have proven your case? Let's see if I can put this in a manner you can understand: **** YOU PATRICK!!! Take your pet, unsupported, unproven theories, and shove them up your ass. If you can't discuss this matter in an adult, intelligent, honest manner, than I have no further use for you. Go use your bullying techniques on someone else. I'm not impressed. Henry was right, I've wasted all the time on you I need to. Goodbye. Phil THAT appears to me to be the honest answer! Since resistor models are less complicated than feedback models, I understandably believe that everyone should use the simpler model until it is proven to be a less accurate description, since humans make fewer errors when using simpler, but equally powerful, models. The simple models INCLUDES THE NFB AND USES VALUES FOR RA which exist because of the NFB. The models DON'T EXPLAIN OR INCLUDE THE NFB MODELS. The models were invented TO BE A SIMPLIFIED TOOL for design purposes. The MOMENT someone proves that feedback is the more accurate model, I will state, publicly, that you were right, and that unless we are working in some situation where there is no significant difference between the two models, we should use feedback to describe triodes. But not until then! And honestly, Patrick, do you not agree that if triodes have feedback, then so do resistors? Resistors have no NFB in the same way pigs don't have wings and cannot fly. Triodes do have NFB because there is an interactive voltage summing of two electrodes which act upon the space charge. I ask you to consider not making yourself look any more ignorant than you appear to be by likening resistors to vacuum tubes in any way. Batteries affect the electric field surrounding the atoms in resistors, and increasing the voltage increases the field strength, just as it does in triodes and diodes, and if it weren't for that, the resistance would be much higher, perhaps infinite. Huh? This is a weird statement and I suggest you consult a professor of electronics to guide you arrange words with more meaning. maybe he'll give you a reading list if you decide to attend his classes at a university. The exams they set at the end of such courses exist to guage whether or not you understand what was in the books you may have read. Mind you, resistors might indeed have feedback, but until we find situations that require us to view them in such a manner, why on Earth would we want to replace the much simpler resistor model for resistors with a feedback model? And the same question applies to triodes and diodes. I suggest you don't know if there is or isn't NFB in resistances. Find out for sure, will you, and let us know what you think and why. You need to know, to understand. Where is you alternative modelling? We have stated it over and over and over again -- well, we've stated the resistor part, perhaps the battery part was not stated as clearly as it should have been -- I don't know how many times we are supposed to repeat ourselves. We agree on the models, but the models includes the NFB in operation. The NFB loop elements are not included in the model because they were designed to allow simple circuit analysis. The triode model is low µ generator and low Ra series resistance, lots of local NFB. The pentode model has high µ gene and high Ra series R, and very little NFB. The model of a vacuum tube as a battery with series R is only correct for DC operartion and is severly limited in its usefulness in applications and the AC model with the battery being replaced with a generator of low Z output resistance whose output = µ x Vg is the accurate model and useful for both DC and AC operation. Unless you understand the operation of the vacuum tube as AC generator with series R for Ra, or else constant current generator = gm x Vg shunted by resistance = Ra then your mind is severly limited for any exercize involving making up circuitry where the current flows can be very basically examined. I see there is NFB in a triode not because I am stubborn, but because it hits me in the eye as being so very obvious, and its missing from all other devices. Yes, it appears to be feedback to you. It appears to be a resistance in series with a voltage to everyone else. There are many more ppl than myself who believe in the NFB withing vacuum tubes. The model of resistance in series with battery or low Z voltage gene has been known for 70 years as a basic tool, and includes the effects of whatever NFB exists. Because you cannot see the NFB, you say it cannot exist. I say that not only is there NFB within vacuum tubes, but also that you are ignorant, and in need of a serious increase in your education and you must forthwith proceed without delay to a nice large pile of books wherin you may find answers you are not getting from me. Until you have read the books, and proved you understand what you have read, you remain someone who is guessing his way through life, unguided by any real knowledge. Patrick Turner. Who is right? Until we have better proofs than anyone has presented, on either side, that "the other side's model" cannot fully account for a triode's behavior, we do not know which one is truly correct, and therefore should use the simpler model, and that is the resistance model. Phil Patrick Turner. Phil |
#70
Posted to rec.audio.tubes
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Explanation still required for triode superiority
Henry Pasternack wrote: "Patrick Turner" wrote in message ... A triode becomes like a diode when its grid is tied to the cathode or at a fixed voltage in reference to the cathode; then there is no Vg-k variation, and no FB either, because TWO voltage changes are required to make the loop for FB to occur. Three days ago, you wrote: The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. But where one maintains the grid bias voltage and fixes the cathode voltage, and simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. Hah. Gotcha there. -Henry Nobody is arguing that a triode with its grid tied to its cathode is anything different to a diode in its behaviour. But as soon as you have active control of the ia or Ea by means of altering the Eg to Ek voltage, then the tube is anything but a diode and a NFB effect operates. The NFB is the summed effect of the two applied voltages of anode and grid with respect to cathode. Got me where? You'll have to try harder my friend to corner me on NFB. Patrick Turner. |
#71
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Explanation still required for triode superiority
Phil wrote: Patrick Turner wrote: Phil wrote: Patrick Turner wrote: Phil wrote: Patrick Turner wrote: [snip] Professor child called the mutual effect of anode AND grid voltages in a triode a form of "self regulation". See Radio Engineering, by Terman, 1937. He does not call it NFB probably because it would have confused ppl at the time who were used to NFB ONLY being some external networking to get an amp of device to display lower Ra thd etc than otherwise it would without NFB. The observation of a triode as a mystery 3 terminal device could be argued to contain NFB. When you have a 300B with Ia = 70mA, Ea = +400V, then if it acted like a resistor without NFB the R value would be 400 / 0.07 = 5,700 ohms. But where one maintains the grid bias voltage and fixes the cathode voltage, abd simply raises the anode voltage by say 80V, then one soon finds that the Ia change = 100mA, and it is because the Ra = 800 ohms, and not the 5,700 ohms of quiescent Ea / Ia . How can this be? Its because the anode has a massive effect on the flow of electrons from the space charge around the cathode to anode despite grid voltage's supposed control of current. One simply cannot deny that a huge anode feedback effect exists, and where you have a grid also able to control the Ia with a gm of about 5mA/V then there MUST be a summing of the anode and grid voltage effects according to some formula ( upon which Professor Child throws more light than I do ) . So its very easy to see that NFB is alive and operational in a triode. [snip] I am not a qualified university educated triodologist. But my powers of observation reveal NFB in triodes to me. But by exactly what process in purely technical terms would you use to allege NFB does NOT exist in triodes? Patrick, you're simply being stubborn at this point. We have pointed out, over and over, that a plate resistance, which, so far, you CANNOT and HAVE NOT proven does not exist, can account for all of the "feedback effects," by which you mean damping, that you talk about. The Ea / Ia at the quiecent state = 5,700 ohms for the 300B I mentioned. But why does it measure 800 ohms when small variations in Ea are made? Because the *model* of a triode includes a voltage offset in series with a diode, caused by the grid. Given, say, -10 Vg, you will get no positive current until you reach a certain plate voltage, enough to overcome the voltage offset caused by the grid. Specifically, the grid can repel the electrons until the plate voltage more or less equals the grid voltage times mu. You get no negative current because a triode only conducts one way, like a diode. Similarly, if you have two resistors in series, with a battery between them, you get no positive current when placing a voltage after the second resistor until its voltage equals the battery placed between the two resistors. A triode acts like a resistor with a voltage offset which is controlled by the grid. All you are doing like nearly everyone else is denying the summing NFB interactive effects of anode voltage AND grid voltage upon Ia, and saying the triode is merely a model of a battery or low Z voltage gene in series with a diode or resistor which is equivalent to Ra. Oh for god's sake WOULD YOU WAKE UP!!! I am fully awake. For the umpteenth time, the fact that some theory fits the known facts regarding the dinosaur's demise DOES NOT MAKE THAT THEORY TRUE! Patrick, no one is denying that you could have a summing effect from plate and grid voltages, and I'm getting tired of you telling me "you don't believe X" when I have told you, over and over, that I have no evidence that X isn't true. I see what consider to be factual, ie, true, and convey such ideas to you, and nothing you have said so far leads me to believe that I should change a syllable I have typed about NFB in triodes. For the umpteenth time, the fact that your feedback theory can explain things does not, and will not ever, BY ITSELF prove that it is true! Why is this so difficult for you to understand? You don't accept evidence that where the sound of "quack, quack" is heard, feathers appertaining to ducks are seen, feet of the bird have webbing, bird can swim well, likes ponds, and also flies long distances. I say a duck is what the bird is; it ain't a sea gull or a goose..... What references or experiments did you perform that PROVED that increasing the voltage across a triode does not simply pull more electrons past all the obstacles in a triode, in exactly the same way that increasing the voltage across a resistor pulls more electrons past the thermally agitated atoms? When did you PROVE that a simple resistance mechanism does NOT exist in a triode? Did you never prove that? Then you cannot rule it out as a possible explanation, period. Basic reasoning 101. Duh. And please, please don't try to tell me that because your theory fits, therefore all other theories are "proven" wrong (see dinosaur example above). I hope I have explained plenty enough. The rest is up to you to learn. I am not the sole authority on NFB in vacuum tubes and to understand you will have to look a lot harder elsewhere. Just be prepared when you read what greater minds than I have written. But you ain't proved there is not any NFB in a vacuum tube. Don't you realise that you will find that proving me wrong is like pushing rice grains uphill with your nose? You would have to be far better equipped with knowledge. And let me say I don't know of any text which conclusively proves NFB does not exist in triodes so you are in an awful position intellectually. A triode becomes like a diode when its grid is tied to the cathode or at a fixed voltage in reference to the cathode; then there is no Vg-k variation, and no FB either, because TWO voltage changes are required to make the loop for FB to occur. What??? You know, up to now, I've thought your feedback model had real merit, and I also thought you straightened out your thoughts on the diode/triode issues, so let's get this straight. If I tie the grid to the cathode, and increase the voltage across the tube, I soon get a current of 100 mA and a dynamic resistance of, say, 600 ohms. But there's no feedback here, according to you. How can there be? its a diode, right, with Eg fixed at EK. One arm of the NFB is present when the tube operates as a diode, but its inactive in any voltage gain application. The NFB in the AC operation is the summed effect of Eg and Ea. If I tie the grid at -50 Vg, and repeat until I reach 100 mA, I again find a dynamic resistance of 600 ohms. And again, according to you, there's no feedback??? But now, if I put in an audio signal, but measure the dynamic resistance, I find that it's 600 ohms, again, at around 100 mA, but NOW there's feedback??? The Ra appears to be 600 ohms because of the electrostatic effect the anode has on Ia. One can't say there is a NFB shunt FB network present when one alters Ea to force the triode into being a diode. Resistors don't work on the same principle. While the anode is free to move with a load, and the load voltage or anode voltage is able to vary due to change to Eg, a NFB effect is evident. Patrick, the whole point about the difference between triodes and pentodes or transistors is that, given a *fixed* grid voltage, changing the voltage across the tube causes a large change in current. Not with a pentode. If the pentode has a fixed Eg1 and fixed Eg2 with respect to Ek, pentodes have a very high Ra... Transistors also have a high Rc.... It has a low output resistance. When the speaker tries to change its voltage due to stored energy, the triode resists this, even if the grid voltage happens to be constant at that time. The load changes or distortion voltages arrising in loads, back emfs et all are opposed by the triode because these signals all oppose themselves because of the electostatic action of the anode upon the Ia. Its the NFB arm working. Screen that arm out with a screen as in apentode and the tube loses control of the load and becomes a current source rather than voltage source. Ppl connect pentodes to loads, and then use global NFB to do exactly what screen FB in UL amps does, or what the screen does in triodes when strapped as such or what the anode is allowed to do in real triodes because there is no screen. Now, you can say that the change in plate voltage changes the flow of electrons to the plate in the SAME WAY as changing the grid voltage, which would be a feedback model. Or, you can say that a triode fails to isolate a basic resistance mechanism which exists in triodes and pentodes -- where increasing the plate or screen voltage draws more current through the spaces between the grid wires, just as increasing the voltage across a resistor draws more current through the atoms -- from the plate voltage. In other words, the screen *isolates* the inherent resistance from changes in plate voltage, which would be a resistance model. So far, so good, but if you think your feedback model requires feedback to "mystically" disappear every time the grid voltage happens to be held steady, then you need to abandon your feedback model, because that's clearly stupid. Mind you, *I* won't abandon your feedback model, because I know that it does apply to diodes, resistors, and triodes with constant grid voltages, and I can accept that. But then, neither do I assume that such a weird model is true merely because it, like other models, happens to fit the facts. The NFB loop is simply the interaction of two fields acting on the Ia. I make a distinction between diode action and triode NFB. Both devices display low Ra ( compared to pentodes etc ) because the anode has an effect on the space charge. The one arm of the NFB loop exists in both triode and diode. This alone does not mean that there is an interactive NFB loop present; certainly not in a diode. We already know all the triode models are true, but true because of the NFB. A claim, backed up by nothing but faulty arguments (meaning you have no proof). But you have no proof I am wrong. In a pentode there is also a battery or low Z voltage gene producing µ x Eg and with an R in series which is equivalent to Ra. In a pentode, µ = gm x Ra and without the NFB, and for a 6AU6 µ approx = 0.0045A/V x 1,500,000 ohms = 6,750 at 7.6mA. We can IMAGINE that the 6AU6 is a voltage gene with an output of 6,6750V for 1V input from a grid, and then we have Ra as a series R = 1.5M and say we have a load of 20k then the current in the Ra + 20k is 6,750V / ( 1.5M + 20k ) = 4.44mA and so the load voltage = 20 x 4.44 = 89V. Thus the tube has a gain of 89. If the load is altered and voltage readings taken then one can deduce Ra = 1.5M If the anode voltage is altered by a low Z voltage source we find Ra = 1.5M although Ea / Ia = 200V / 0.0076A = 26.3k, so how come we measure the Ra at 1.5M? Its because there is VIRTUALLY NO NFB, the opposite case to a triode. Or because the pentode shields its inherent low resistance -- and if you change the screen voltage, you will quickly see that such a low resistance exists -- from changes in plate voltage. Once you start altering the screen voltage as well as the grid voltage and allow Ea to move on a load, or a CCS, then you have 3 things interacting to produce a given Ia or Ea and things get much more complicated. I have not time to talk about such tube operation and the math involved is also very complex. if you really knew anything at all, you'd know all the math regarding triodes easily, and find that math involving pentodes a real doddle as well and be able to explain it all to us, rather than I be forced to explain a few things clumsily as I may manage to you... I am not university trained, but I believe I have the concept of triodes right and that i know enough about pentodes & tetrodes to say what happens when one is connected in an amp with say 20% of CFB connected locally around the OPT. The math isn't as easy as it looks I may add, and someone told me that if ever I wanted to understand electronics I'd have to be very good at maths. I get by with my limited math ability, so my ears and meters and CRO tell me. But where is your deep understanding? All you have proven yourself to be is a knocker, a doubter, and based exactly upon what? Reasoning 101, the presence of one possible explanation DOES NOT PRECLUDE other possible explanations. The existence of the phlogiston theory of combustion did not prove that the Lavosier's oxygen theory of combustion was false. If we connect the screen to anode, and triodise the 6AU6, then the anode voltage is allowed to affect the Ia and the apparent Ra drops because the µ drops from 6,750 to 36 due to NFB OR because you are no longer shielding the low resistance from changes in plate voltage. Tell me again, what does the NFB model achieve that the low resistance model does not? The low resistance of triode operation is because of the anode voltage effect on Ia. One arm or the loop NFB is allowed to operate, so it operates, OK? and the Ra = µ / gm = 36 / 0.0048 = 7,500ohms, so the NFB has a large effect on reducing Ra. What other mechanism do you suggest causes Ra to be so reduced? The existence of a shield/screen that prevents changes in plate voltage from accessing the low internal resistance, just as we have said (in so many words) all along. Then we should consider the case of a triode where there is NO ANODE CURRENT CHANGE IN THE OPERATION. Okay, I'll bite. Who knows? Maybe you'll actually prove that NFB is indeed the preferred explanation. I would prefer I share my observations and let you find your own truth. The truth comes from proof, and if you don't accept my observations as proof then you should never sleep again until you either proove to yourself what is true one way or another, and I see you are sleeping and not prooving anything to anyone. This is where there is a CCS load, and no anode current occurs. No changes in plate current. Got it. The summed effect of the grid and anode voltage upon the space charge remains. So? In other words, we can continue to view this situation using the NFB model. Fine, that means that it has not so far been proven false. That fact tells us NOTHING about the resistance model. R = E / I. So where no current change occurs, R becomes infinite. So some other way of thinking about the triode other than being a glorified resistance must be considered. Why does it operate so linearly when no Ia and only an Ea change occurs? Most triodes are considered linear over small Ea changes with CCS loads. The 300B is capable of 140V peak +/-V swing at about 1% THD only with CCS load, how come the bloomin things does so much better than pentode, tetrode or any SS device as a voltage amp? Its not sufficient to say well, it just does it, because its like some kind of resistor. That's not a deep enough answer. So find the answer. NO anode current change is possible because of the infinite resistance of the load. True. The NFB effect is maximal and voltage gain = triode µ. Whatever (but Av = u, true). Witha 6AU6 pentode with CCS, the µ = gain and would be 6,750 because there is a very small VOLTAGE caused NFB effect. Or, the resistance is not completely shielded from the plate voltage, preventing u from being infinite. True. How does one explain the tube working with CCS load without thinking of the amounts of local NFB???? What's your point? In both cases, the grid-cathode voltage MUST change if you are to change the plate-cathode voltage, although you need to change it less with a pentode. So? With an unshielded resistance, the grid-cathode voltage must change more to compensate for that unshielded resistance. So? That's just another viewpoint of the same low plate resistance of a triode. One day you'll be able to think of 2 things at once while they are working together. Not today it seems. if there was no FB and the tube was just a purely passive device like a resistor, the changes in Ea would give Ra = 5,700 ohms. but we get 800 ohms. How come? See above. You don't explain it. I did explain it, you merely didn't understand it (which might not be your fault). The voltage in series with a resistance model means that you get no current at all until Vp is approximately mu x Vg, at which point the 800 ohm resistance comes into play. That's the model, and it correctly describes triode behavior. Yes, in the absence of tests which possibly can distinguish between anode resistance and triode feedback, we really don't know which it is. But to claim that feedback must exist *because* effects equivalent to either feedback or low plate resistance exist is unscientific. You have a choice, and that is why the rest of us simply state that, in the absence of any logical, intellectual, or engineering advantage for feedback, we prefer low plate resistance as a *model*. That's our choice. Maybe the other choice is better. But you have not given any analysis to my knowledge which proves that such a choice does not exist, or even that a feedback model is a better choice for audio or electronics. You call me stubborn, and refuse to proove I'm wrong, and you cannot deal with the idea of the mutual effect of the two changing voltages of grid and anode which BOTH have large effects on the Ia and so who is right? If say I am wrong, then so is Prfessor Child, and all the guys with better minds than yours or mine. I call you stubborn because you claim that feedback exists, when an alternative model explains everything (admittedly, as far I know) just as well. I won't call you stubborn. The "alternative models" of a triode have been known by many for 70 years and are explained at my website and we agree on the models of battery/voltage gene with series R to represent Ra. But you still fail to see the NFB that exists. Be fair and accurate here; I still fail to see a PROOF that NFB correctly describes a triode, while resistance (plus a voltage) does not. The models of generator + Ra resistance DO NOT explain or even include the NFB effects, but are the models of the tube working AFTER TAKING INTO ACCOUNT WHATEVER NFB EXISTS. I have no idea what your point is here. I am beginning to think there is no point in trying to get you to see anything. To say that it *might* be feedback would be okay, but until you have proofs or experiments that rule out the resistor model, you cannot say definitively that triodes have feedback. I leave you to consider that minds better than yours have concluded there is NFB within a triode. That is merely an argument, an indication method, not a proof. By the way, which better minds are you thinking of? The plate may simply pull electrons along in exactly the same manner as a battery pulls electrons through an ordinary resistor. No such pull along effect occurs in resistors. Oh really? Pray tell how a resistor does work. I am not going to tell you now. I ain't got time. I am here for the tubes and I have to refuse explantations of the really basic stuff when you show everyone you are so lazy for not reading up all about it elsewhere. There IS much more on resistors for you to read first, so i won't have to tell you, ever, or the group, some of whom have studied resistors perhaps more than you have. A resistor works in an entirely different manner to any tube. Which would be ... Then again, perhaps it would be *best* described as feedback, and I can easily admit that. The NFB is only evident when one considers the COMBINED NET EFFECT OF TWO VOLTAGES within the tube, ie, grid and anode voltages. Ridiculous, the low impedance of a triode is quite intact when the grid voltage is fixed. If not fixed, the Ra of the triode may be made as high as one wishes. Furthermore, simply remove the grid from a triode (there are several rectifiers where this was done), and I guarantee that the dynamic resistance for a given plate voltage will be about the same as in the triode version when the grid is tied to ground, and yet you're claiming that the diode version does not have feedback, and therefore should have a much higher resistance. Select equal current levels for the diode version and the triode version using several fixed values for the grid voltage, and you still get equal dynamic resistances. Put an audio signal in, and measure the dynamic resistance at some moment in time, you will still get the same values for a given current level. If a triode has feedback, then a diode has feedback. That is NOT enough to make me abandon the NFB model -- although it gave me pause for a while -- why should you feel it's necessary to DENY that a diode has the same feedback mechanism you claim exists for triodes? Only one arm of the NFB loop is working when the input voltage is into the anode circuit of a diode or into a triode anode when Eg = Ek or at a fixed voltage relative to Ek. Where Ea is the output voltage as a result of input Eg, then a NFB loop exists where such a two component loop cannot existin in the diode. However, Henry has some very convincing lines of reasoning that show no advantage or greater accuracy or anything like that for feedback, I have not been able to find lines of reasoning to contradict him, and again, as far as I know, neither have you! I don't have to prove that triodes do not have feedback to "prove you wrong," when all I am trying to claim is that you are not necessarily right! Try reading a few more books about triodes rather than seeking some NFB de-bunking premise from Henry. With all due respsect to Henry, he ain't the world's authority on vacuum tube theory. He could be the devil himself, but that's irrelevant, along with his knowledge, when it comes to the quality of his arguments on this matter. You don't "disprove" a theory by saying the author is stupid or evil. You ignore the characteristics of the author altogether, and focus on the accuracy, or lack thereof, of the theory itself. Reasoning 101. Its sometimes easy for me to discredit a theory without proof as i have at times. I have not the time to be any better; I plead that I am human, and thus cannot really change the minds fixed around me. I will make to fine tubed amplifiers while the rest of everyone goes about their business in perhaps greater ignorance than i have. I seek to prod people to read and learn more rather than call me a liar. Its really all i have time for, since explaining what I do know to the group to maintain some semblance of a pool of tube craft knowledge is voluntary, and goes unpaid, so this may be the ONLY place when your precious beliefs are challenged at all, and those who don't expect to be challenged are living in an intellectual la-la land of ignorant fairies. Nor am I. So read up elsewhere. Until you have read a lot more, consider yourself ignorant, because that would be a fact. A general criticism without any support or examples. An old debating trick. Useless ... Let me see if I can make this clear. Let's assume, for a moment, that a test will appear that truly can distinguish between low impedances caused by feedback, and low impedances caused by a low impedance, a simple resistance. Resistances can be any value, and characterized by being a fixed value for a large range of currents and frequencies. The point was to assume, to hypothesize, that a test capable of distinguishing between a NFB model and a resistance model exists. Given that hypothesis ... I do not know for certain what that test would tell us about triodes. As far as I can tell, neither do you. Well you are not able to hear or see what I have been saying. That would indeed be one explanation. Another would be just the reverse, that you insist on ignoring the fact that without a proof that one model is correct, and the other model incorrect, you cannot justifiably claim that the low output impedance of triodes is definitely due to a feedback mechanism. You don't want to accept you are mostv likely to be wrong, and ignorant. That put-down doesn't necessarily follow from facts; it's just another unsupported criticism, and therefore useless. You have read almost nothing, have not benefitted from education, and are at a similar position of where you might think you know your stomach's anatomy by gazing at your navel. **** you, Patrick. You know, every once in a while I think that Ian is right; you're a bully. I knew sooner or later I'd be told to get stuffed and be told that i was a bully. Ian went around giving lots of advice on tube craft issues and he didn't even have a copy of RDH4; its like being a Catholic priest without having a copy of the bible. After some embarrassment and argy bargy and angst he has yet to forgive me for he went and bought a copy of RDH4. Then he enjoyed ridiculing much of its truth. I think he succeeded in making a fool of himself, but I continued to challenge his BS for years ever since. he hasn't to my knowledge accepted NFB in triodes either, and I don't bother to argue with him. I just say where I think he's wrong and move right along. Its a public forum and whatever you believe in is challengeable. That is the function of a discussion group. People call me a lotta names and its all water off a ducks back. Or at the very least, you act like one. Let me get this straight. I'm just a stupid **** because I don't believe you have proven your case? Let's see if I can put this in a manner you can understand: **** YOU PATRICK!!! Take your pet, unsupported, unproven theories, and shove them up your ass. If you can't discuss this matter in an adult, intelligent, honest manner, than I have no further use for you. Go use your bullying techniques on someone else. I'm not impressed. Henry was right, I've wasted all the time on you I need to. Goodbye. Fine, go away from the disission as ignorant as you came into it. The people with real knowledge must be smiling at you. I knew I'd get you sore when I said you hadn't read much. Let's face it, you ain't read much at all abouty NFB in triodes, and you know so little. You ask so many questions and expect ME to prove it easy to you, like spoon feeding you like a baby. Sorry, but spoon feeding adults turns them into selfish brats, so go learn about how and what happens in triodes and resistances some where else if you can't find see any truth as i see it. No hard feelings, just desire that you do more to educate yourself. Patrick Turner. Phil THAT appears to me to be the honest answer! Since resistor models are less complicated than feedback models, I understandably believe that everyone should use the simpler model until it is proven to be a less accurate description, since humans make fewer errors when using simpler, but equally powerful, models. The simple models INCLUDES THE NFB AND USES VALUES FOR RA which exist because of the NFB. The models DON'T EXPLAIN OR INCLUDE THE NFB MODELS. The models were invented TO BE A SIMPLIFIED TOOL for design purposes. The MOMENT someone proves that feedback is the more accurate model, I will state, publicly, that you were right, and that unless we are working in some situation where there is no significant difference between the two models, we should use feedback to describe triodes. But not until then! And honestly, Patrick, do you not agree that if triodes have feedback, then so do resistors? Resistors have no NFB in the same way pigs don't have wings and cannot fly. Triodes do have NFB because there is an interactive voltage summing of two electrodes which act upon the space charge. I ask you to consider not making yourself look any more ignorant than you appear to be by likening resistors to vacuum tubes in any way. Batteries affect the electric field surrounding the atoms in resistors, and increasing the voltage increases the field strength, just as it does in triodes and diodes, and if it weren't for that, the resistance would be much higher, perhaps infinite. Huh? This is a weird statement and I suggest you consult a professor of electronics to guide you arrange words with more meaning. maybe he'll give you a reading list if you decide to attend his classes at a university. The exams they set at the end of such courses exist to guage whether or not you understand what was in the books you may have read. Mind you, resistors might indeed have feedback, but until we find situations that require us to view them in such a manner, why on Earth would we want to replace the much simpler resistor model for resistors with a feedback model? And the same question applies to triodes and diodes. I suggest you don't know if there is or isn't NFB in resistances. Find out for sure, will you, and let us know what you think and why. You need to know, to understand. Where is you alternative modelling? We have stated it over and over and over again -- well, we've stated the resistor part, perhaps the battery part was not stated as clearly as it should have been -- I don't know how many times we are supposed to repeat ourselves. We agree on the models, but the models includes the NFB in operation. The NFB loop elements are not included in the model because they were designed to allow simple circuit analysis. The triode model is low µ generator and low Ra series resistance, lots of local NFB. The pentode model has high µ gene and high Ra series R, and very little NFB. The model of a vacuum tube as a battery with series R is only correct for DC operartion and is severly limited in its usefulness in applications and the AC model with the battery being replaced with a generator of low Z output resistance whose output = µ x Vg is the accurate model and useful for both DC and AC operation. Unless you understand the operation of the vacuum tube as AC generator with series R for Ra, or else constant current generator = gm x Vg shunted by resistance = Ra then your mind is severly limited for any exercize involving making up circuitry where the current flows can be very basically examined. I see there is NFB in a triode not because I am stubborn, but because it hits me in the eye as being so very obvious, and its missing from all other devices. Yes, it appears to be feedback to you. It appears to be a resistance in series with a voltage to everyone else. There are many more ppl than myself who believe in the NFB withing vacuum tubes. The model of resistance in series with battery or low Z voltage gene has been known for 70 years as a basic tool, and includes the effects of whatever NFB exists. Because you cannot see the NFB, you say it cannot exist. I say that not only is there NFB within vacuum tubes, but also that you are ignorant, and in need of a serious increase in your education and you must forthwith proceed without delay to a nice large pile of books wherin you may find answers you are not getting from me. Until you have read the books, and proved you understand what you have read, you remain someone who is guessing his way through life, unguided by any real knowledge. Patrick Turner. Who is right? Until we have better proofs than anyone has presented, on either side, that "the other side's model" cannot fully account for a triode's behavior, we do not know which one is truly correct, and therefore should use the simpler model, and that is the resistance model. Phil Patrick Turner. Phil |
#72
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Explanation still required for triode superiority
"Patrick Turner" wrote in message ...
Got me where? You directly contradicted yourself. Three days ago, you argued that the nonlinear plate resistance of a triode with Vgk FIXED is proof of NFB at work. But yesterday, you stated the opposite, that NFB DOES NOT EXIST with Vgk fixed. Which is it? By your reasoning, if I have a common-cathode amplifier with an AC signal on the grid, the output resistance of the tube will be low due to NFB. But if I take away the signal, leaving only a fixed DC bias on the grid, the NFB will disappear and the output resistance will rise dramatically. You and I both know this doesn't happen. By the way, did you know I studied EE in Frederick Terman's department? He was professor emeritus, until he died, while I was at university. Some of my professors were his former students, including a legend or two from the "golden age" of tube radio, plus a good share of more modern legends. I mention this because you raised the issue of academic credentials yesterday. I have to say, Patrick, you really don't know how to make a correct or convincing engineering argument. And I do have the credentials to say that. You are straining my patience. -Henry |
#73
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Explanation still required for triode superiority
In article ,
"Henry Pasternack" wrote: "Patrick Turner" wrote in message ... Got me where? You directly contradicted yourself. Three days ago, you argued that the nonlinear plate resistance of a triode with Vgk FIXED is proof of NFB at work. But yesterday, you stated the opposite, that NFB DOES NOT EXIST with Vgk fixed. Which is it? By your reasoning, if I have a common-cathode amplifier with an AC signal on the grid, the output resistance of the tube will be low due to NFB. But if I take away the signal, leaving only a fixed DC bias on the grid, the NFB will disappear and the output resistance will rise dramatically. You and I both know this doesn't happen. By the way, did you know I studied EE in Frederick Terman's department? He was professor emeritus, until he died, while I was at university. Some of my professors were his former students, including a legend or two from the "golden age" of tube radio, plus a good share of more modern legends. The crucial question is did any of the wisdom of these giants rub off on you while you put in your time there. Regards, John Byrns |
#74
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Explanation still required for triode superiority
"John Byrns" wrote in message ...
The crucial question is did any of the wisdom of these giants rub off on you while you put in your time there. All I can say is I was fortunate to have the chance to learn from these people. Here's a somewhat funny anecdote. When I graduated, I was applying for a job at SRI International. Apparently they thought I was smart, but found me to be quite obnoxious. Oswald G. "Mike" Villard (look him up), who was retired by this time but working part-time at SRI, put in the good word for me and I got the job. In the end, it worked out well. I looked up Villard on Wikipedia last night and found out that he died in 2004. He was the real deal, a true pioneer and a heck of a nice guy. I really had no clue at the time what a privilege it was to associate with people like him. -Henry |
#75
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Explanation still required for triode superiority
John Byrns said:
In article , "Henry Pasternack" wrote: By the way, did you know I studied EE in Frederick Terman's department? He was professor emeritus, until he died, while I was at university. Some of my professors were his former students, including a legend or two from the "golden age" of tube radio, plus a good share of more modern legends. The crucial question is did any of the wisdom of these giants rub off on you while you put in your time there. Dunno about that, but his analysis about the alleged feedback in triodes (or absence thereof) made a lot of sense to me (at least the parts that I could understand). Henry seems to know his stuff pretty well. I'm not that well versed in the theoretical department, so maybe it's all flying over my head, but the conclusions that Henry posted and as they were perceived by me, are at least uinderstandable and, what's even more for a simple techie like me, cover the bases well enough to not worry about it when designing my hobby amps with triodes ;-) -- "Due knot trussed yore spell chequer two fined awl miss steaks." |
#76
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Explanation still required for triode superiority
Henry Pasternack wrote: "Patrick Turner" wrote in message ... Got me where? [snip] By the way, did you know I studied EE in Frederick Terman's department? He was professor emeritus, until he died, while I was at university. Some of my professors were his former students, including a legend or two from the "golden age" of tube radio, plus a good share of more modern legends. I mention this because you raised the issue of academic credentials yesterday. I have to say, Patrick, you really don't know how to make a correct or convincing engineering argument. And I do have the credentials to say that. You are straining my patience. -Henry Congratulations, Patrick. You've just won the arguments hands down. Henry Pasternack is known as Pompass Plodnick among other reasons because he is a pompous asshole who every time he loses an argument tries to steamroller with his diploma those he cannot beat by argument. He is called Plodnick among other reasons because he is clearly a plodder who learned a certain minimum of electronics off by rote, and anything he did not learn off by rote is terra incognito to him. And, as I explain to Phil in a concurrent post in this thread, Pasternack is apt to lie on professional matters for the trivial satisfaction of winning an argument; the "nick" part of his nickname is because he is dumb Polack who always gets caught out in his lies. Google is full of examples of Plodnick losing the argument and then bragging about his education, being caught out in deliberate professional for personal reasons, and suchlike immoralities. Two other points are worth making. It is a shame that all that money was spent on "educating" a fool like Pasternack when in effect it merely assured that some bright, more worthwhile but poor kid didn't get an education; such waste and misallocation of resources is almost enough to turn one into a socialist. And it must be said that when a man pushing 50, like Henry Pasternack, aka Pompass Plodnick, has to justify himself by bragging about his education, you may be absolutely certain in the assumption that his elite education bought him only the most disappointing of careers, because the paymasters were not taken in. If employers are not taken in by the quarterwit Pasternack's diploma, we needn't be either. Andre Jute Impedance is futile, you will be simulated into the triode of the Borg. -- Robert Casey, funniest RAT of them all |
#77
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Explanation still required for triode superiority
John Byrns wrote: "Henry Pasternack" wrote: [snip] By the way, did you know I studied EE in Frederick Terman's department? He was professor emeritus, until he died, while I was at university. Some of my professors were his former students, including a legend or two from the "golden age" of tube radio, plus a good share of more modern legends. The crucial question is did any of the wisdom of these giants rub off on you while you put in your time there. Regards, John Byrns Pasternack's transparent namedropping is intended to imply that the wisdom of Terman and his best students rubbed off on him. It's bull**** of course. Next Plodnick will claim that Worthless Wiecky is the equal of Peter Drucker (1) because Worthless was the janitor at the Wharton School of Business! (2) Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review (1) Peter Drucker was the greatest theorist of applied economics (business management) who ever lived. (2) Yes, my darlings, I know where the Philadelphia is, and I know where New York is, but if we're dropping names, what's few miles? Reminds me of the time when the chairman of my ad agency had this brilliant idea (he was always having brilliant ideas unless we were extra-vigilant): we would hire Drucker as a consultant. So a deputation of the directors went immediately to Drucker's office to make him an offer he couldn't refuse. My chairman was a huge fellow in his early thirties with short, very blond hair. The rest of us were muscular young men (high-profile sporting achievements were essential to rising in our organization -- that's how we met most of our clients) of definitely Aryan stock. We all wore double-welted leather-soled shoes from Lobb in London and you can bet your ass a bunch of young guys who earned seven-figure sums walked down this long passage before Drucker's office with heel-clattering confidence; most of us had been in the military somewhere (this was still in the age of conscription, where to avoid forcible induction you did ROTC) so we clattered in step, like a firing squad marching. Drucker was a Hungarian, a refugee from the Nazis... One of the PA flung the door open dramatically and we bent our heads to get through the door, then stormed up to a halt before the desk behind which this little guy cowered. My chairman said, "We have come for you!" Drucker stuttered, "I'm an American citizen now!" Needless to say, we didn't succeed in hiring him. |
#78
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Explanation still required for triode superiority
Phil wrote: Patrick Turner wrote: Try reading a few more books about triodes rather than seeking some NFB de-bunking premise from Henry. With all due respsect to Henry, he ain't the world's authority on vacuum tube theory. He could be the devil himself, but that's irrelevant, along with his knowledge, when it comes to the quality of his arguments on this matter. You don't "disprove" a theory by saying the author is stupid or evil. You ignore the characteristics of the author altogether, and focus on the accuracy, or lack thereof, of the theory itself. Reasoning 101. Unless of course the party in question has a track record of deliberately lying. In the case of Henry Pasternack, often referred to RAT as Pompass Plodnick, Google archives show a long history of Pasternack lying on professional and other matters for the sake of "winning" some argument, and of Pasternack committing other unscientific and immoral acts, for which his only excuse is, once the further lies are stripped away, in Pasternack's own words, "my zeal to flame Andre". In this particular case Pasternack came here hoping to have a big fight with me but I merely patronized him a little and sent him on his way with a flea in his ear; he was stuck with Patrick. Because Pasternack came for me first, and because of his history of lying on professional matters for personal gratification, and because Pasternack's first post on the subject (to Chris Hornbeck) was ambiguous, we don't actually know whether he really believes what he says now, or whether his hatred of me has once more painted him into another corner which he will now try to justify with a berm of math. Those new to RAT who wish to see earlier examples of Pasternack lying on professional matters for personal gratification should look up the case where Pasternack told a newbie not to listen to me when I advised a primary impedance on his output transformer 2*Rp or higher; Pasternack told him instead to choose an output impedance equal to the plate resistance. Read that again. Pasternack surely knew that the primary impedance should be twice or more the plate resistance but he lied about it to a newbie "in my zeal to flame Andre". There are hundreds of further posts in Pasternack which tried to justify his Zo = Rp stance but eventually John Byrns nailed Pasternack's hide to wall. Other examples are plentiful, and I have already in this thread given references to a URL that proves Pasternack's contempt for the scientific method. Furthermore, Pasternack in the throes of his hatred will commit totally immoral acts. He ran with Michael LaFever's Magnequest Scum, who flooded the single driver conference with graphic homosexual pornography sent in my name in an effort to drive me out; they were not there before I came, they were not there after I left. Some of that was traced to Pasternack's server. Even worse is the case of the two little girls of an Italian engineer who built one of my designs. He accused Pasternack of sending graphic homosexual filth to his computer, where his two little girls saw it. He didn't even know who Pasternack was when he traced the filth to Pasternack. Pasternack's Magnequest Scum associate Bob Chernofsky said on the Joenet (there's an archieve at Harvard if you want to look it up; search for Sound List) that Pasternack did it because he was bored with not being able to get at me directly. Do you really want to hold this scumbag Pasternack up to us as an impartial fount of engineering wisdom? Get real, Phil. We know better, and it is up to newbies like you to inform themselves before they goof up dumb opinions. Andre Jute Stop bleating. Please, please, please give me the Silence of the Lambs. PS Do I need to explain that we shall know by your response to my sharp remarks how steady your judgement is? |
#79
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Explanation still required for triode superiority
In article , Sander deWaal
wrote: John Byrns said: In article , "Henry Pasternack" wrote: By the way, did you know I studied EE in Frederick Terman's department? He was professor emeritus, until he died, while I was at university. Some of my professors were his former students, including a legend or two from the "golden age" of tube radio, plus a good share of more modern legends. The crucial question is did any of the wisdom of these giants rub off on you while you put in your time there. Dunno about that, but his analysis about the alleged feedback in triodes (or absence thereof) made a lot of sense to me (at least the parts that I could understand). Henry seems to know his stuff pretty well. This discussion isn't a matter of knowing much of anything, if I read Henry correctly he is not saying that the operation of the triode doesn't involve NFB, or that it does for that matter, all Henry is saying is that there are several alternate ways to describe the operation of the triode when it is viewed as a black box. Henry's logic can equally well be applied to other devices, like say the famous Williamson amplifier, to describe their operation without reference to NFB. The fact that a device can be described by a Thevenin or Norton equivalent circuit says nothing about whether or not the device makes use of NFB as part of its internal operation. Given that both viewpoints are valid in a mathematical sense, this whole discussion is just so much pointless gum flapping. I should note that I only rejoined this group a week ago, and while there appear to be numerous threads that may be discussing this subject, I have only looked at two, first the "Diode" thread, and today this thread. Since I have been only selectively reading the posts here, I may be missing some crucial history which could render some of my comments invalid, YMMV. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
#80
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Explanation still required for triode superiority
"John Byrns" wrote in message ...
This discussion isn't a matter of knowing much of anything, if I read Henry correctly he is not saying that the operation of the triode doesn't involve NFB, or that it does for that matter, all Henry is saying is that there are several alternate ways to describe the operation of the triode when it is viewed as a black box. That is one of my conclusions, but not necessarily the most important one. The main purpose of my postings has been to dissect the triode NFB claims, and to debunk them -- carefully and critically. Doing so requires both knowledge and analysis skill. You always try to diminish what I have to say. You're just far more restrained than Andre. -Henry |
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