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#41
Posted to rec.audio.tubes
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pentode amplifiers
On Nov 3, 9:30 pm, robert casey wrote:
If you mean can you use one half of a PP output transformer for SE, the answer is most definitely no. An SE transfomer is distinguished from a PP one by an air gap. There is a way to use a transformer without an airgap for SE; it is called parafeed, to indicate that the B+ is shunted in parallel to the transformer primary, so that the output doesn't carry the current and can therefore be designed to a more relaxed specificaiton. You also need a big blocking cap, which some say is out of the signal and some say can be heard; you make your choice and take your chances. One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to the effort to build a power supply to supply that and the tube's side. So nobody ever does that, except maybe only if someone has on hand some P-P output transformers but insists on single endedness. But it would be a kludge... :-) Or regap that transformer, but you could ruin the sound quality that was designed into it (I'm not familiar with transformer design, but I've since learned not to waste time fooling with power transformers in audio output work :-) ). You could use the old centertap as a kind of UL tap, but the tap position is not optimal for UL work. But you'd be best off saving the P-P transformers for another project, and get single ended transformers that were designed for that service instead. hey-Hey!!!, What you describe is one of the methods to do DC current cancelling. The other half of the PP primary is straightforward to implement, it takes the same current as the tube idling opposite it. One can also use heater current. Best SE amp I ever heard was a 50W monster that had a piddling little output TX. Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. cheers, Douglas |
#42
Posted to rec.audio.tubes
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pentode amplifiers
In article .com,
Multi-grid wrote: On Nov 3, 9:30 pm, robert casey wrote: One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to the effort to build a power supply to supply that and the tube's side. So nobody ever does that, except maybe only if someone has on hand some P-P output transformers but insists on single endedness. But it would be a kludge... :-) hey-Hey!!!, What you describe is one of the methods to do DC current cancelling. The other half of the PP primary is straightforward to implement, it takes the same current as the tube idling opposite it. One can also use heater current. Best SE amp I ever heard was a 50W monster that had a piddling little output TX. Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. hey-Hey!!!, Multi-grid, can you give us a few more details on the design of this amplifier? I assume it used some sort of DHT transmitting tube, hence the need for a DC heater supply? To keep from dumping a substantial portion of the audio power generated by the tube into the tube's heater, I assume there was also a suitable inductor connected in series with the heater circuit and the "special winding" on the OPT, to provide a high non lossy impedance to the audio frequency currents? Given the need for this special inductor one wonders why the builder of this amplifier didn't simply go with the conventional parafeed scheme, whose inductor would presumably use a core of a similar size to that required with this DC cancelation scheme. The parafeed arrangement seems like a better more straight forward approach, and as a bonus provides additional attenuation of any ripple on the B+ power supply. I assume the reason for this design was that the builder wanted to build something unusual and unlike anything else seen before? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#43
Posted to rec.audio.tubes
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pentode amplifiers
Jute:
If you mean can you use one half of a PP output transformer for SE, the answer is most definitely no. An SE transfomer is distinguished from a PP one by an air gap. There is a way to use a transformer without an airgap for SE; it is called parafeed, to indicate that the B+ is shunted in parallel to the transformer primary, so that the output doesn't carry the current and can therefore be designed to a more relaxed specificaiton. You also need a big blocking cap, which some say is out of the signal and some say can be heard; you make your choice and take your chances. Casey: One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to the effort to build a power supply to supply that and the tube's side. So nobody ever does that, except maybe only if someone has on hand some P-P output transformers but insists on single endedness. But it would be a kludge... :-) Or regap that transformer, but you could ruin the sound quality that was designed into it (I'm not familiar with transformer design, but I've since learned not to waste time fooling with power transformers in audio output work :-) ). You could use the old centertap as a kind of UL tap, but the tap position is not optimal for UL work. But you'd be best off saving the P-P transformers for another project, and get single ended transformers that were designed for that service instead. Multi-grid: hey-Hey!!!, What you describe is one of the methods to do DC current cancelling. The other half of the PP primary is straightforward to implement, it takes the same current as the tube idling opposite it. Okay, but wasteful. One can also use heater current. Best SE amp I ever heard was a 50W monster that had a piddling little output TX. Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. cheers, Douglas It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. 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 |
#44
Posted to rec.audio.tubes
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pentode amplifiers
John Byrns wrote: In article CfGWi.1359$8S5.242@edtnps82, "Dave" wrote: "Andre Jute" wrote in message ups.com... And NFB up the kazoo. 0.1 per cent is a figure commonly bandied about but I'm not overly impressed. I know for a fact that people cannot hear as much as 3/4 per cent second harmonic but can hear that much odd harmonic very clearly, and many people can hear or are made uncomfortable by 0.3 per cent odd harmonics. What you want to do is not to measure at full power but at some lower power where you will actually use the amp; 1W or 2.83V into 8ohm is a common level with even semi-sensitive speakers. So... is ALL negative feedback bad? I am 40 with some background in electrical engineering and learned nothing but transistor theory at school... thermal runaway pretty much mandates feedback in all transistor amps. There are typically two different feedback mechanisms at work in a transistor amplifier. The first, which is the one you are referring to stabilizes the DC bias, or operating point, of the transistors to prevent thermal runaway as you describe, and also to insure that the "crossover" region of the transfer characteristic has the desired degree of overlap. The second is the overall loop NFB, which is what Andre is talking about, and is used to reduce the audio frequency distortion and noise produced in the amplifier, as well as to stabilize the gain of the amplifier, as the gain of discrete transistors is notoriously inconsistent from sample to sample. You left out one other very important common NFB loop. This is the connection of the output transistors as emitter followers, reducing the gain of the output stage to nearly 1.0. This is often an amount of local series voltage NFB = about 40dB. The global series voltage NFB is applied after the EF connection and back to input which subjects the driver amp and output stage already with its 40dB of local NFB to perhaps 60dB of NFB over all. A lot of what I read about 'audiophile' grade amps is pro-znfb. Why? It's because of a lack of understanding in the audiophile community. NFB can work wonders when correctly applied by someone who knows what they are doing, but it can also do serious harm when incompetently applied. Bad experiences with amplifiers using NFB of the latter type lead to the typical audiophile' negative feelings towards NFB. Indeed... Patrick Turner. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#45
Posted to rec.audio.tubes
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pentode amplifiers
Andre Jute wrote: On Nov 2, 4:28 pm, Patrick Turner wrote: Andre Jute wrote: On Oct 31, 2:41 pm, "Dave" wrote: Is there any quick "in a nutshell" explanation why there aren't more pentode amp designs? I'm guessing it has to do with extreme non-linearity. I am building a 10W EL84-based ultralinear amp. The triode conversion is a snap but it drops me down to 5W which is not enough oomph for my 88dB speakers. Pentode mode would give me 15W which I am inclined to try if it's not too difficult. Can anybody point me to a resource where I could figure out the proper screen voltage required for pentode mode EL84's with an 8K output tranny and a B+ of 300V? does this voltage have to be regulated, or could I just drop the B+ with a resistor? Thx Dave I wasn't aware of a shortage of pentode amps. But a pentode amp has more gain than those with ultralinear connection, and thus can have more global feedback applied, and thus lower THD. However, I put a pentode/ultralinear/triode switch and a variable/off negative feedback switch in the best amp I ever designed, my T113 "Triple Threat", Class A1 PP EL34 of pretty straightforward, conservative design. Then I tested it with chamber musicians listerning to their own recordings. They universally hated the pentode sound, and loved the triode sound, on which the amp is usually played with zero NFB. The explanation is simple. Loop NFB causes artifacts of ever lower magnitude but higher order. These high order distortions, even at 60dB below conscious perception are very, very disturbing, whereas second harmonic up to three-quarter per cent cannot even be distinguished by professional musicians. It is a subliminal effect, and of course in pentode mode it is exaggerated. People look at the total harmonic distortion but in fact the higher harmonics must be weighted much more heavily than the second harmonic to account for its extraordinary subliminal effect, often described as "edgineess" by professional musicians. -60dB, at average listeining levels???? Say a volt is average, then -60dB artifcats = 1mV. 1mV of grunge isn't exactly loud in most speakers...... Try Quad ESL, though of course not at 1W. ESL are generally so insensitive that residual amp noise isn't heard above recorded venue noise and 1mV of grunge isn't heard. Or try horns at 1W. 1mV of ****e matters not with horns as well because the same SNR would apply. The volume control isn't selective about letting the grunge through when attenuating the music. So with horns, one just uses less vome than with the ESL. A volt into horns is deafening. But Becase horns require maybe 1/10 of the voltage of ESL or "normal" modern speakers, the amp can be SET and not be producing many IMD products. THD & IMD reduces with reduced power levels. You'd be amazed what you can hear. Sometimes I am indeed amazed at what I hear.. About half of professional musicians can are still disturbed by the artifacts at 60dB below; that's more than enough for me to believe in subliminal perception of IM artifacts. Not all musicians are sensitive to 60dB artifacts. In fact huge differeneces in hearing abilities range across the population generally, including musician types. Do we include Sid Vicious, of punk rock fame? Mick Jagger perhaps? Is Nigel Kennedy likely to hear -60 dB artifcats any better than anyone else? Does Nigel use a special triode amp? Most "musos" in the rock'n'roll field don't like unaltered music. THeu only really like artifacts when up at about the 15%+ level and have reverb added, and where recordingsd are made they usually really hate the sound of their own voise, and want the recording studio to process it all so heavily to make it at all saleable, and maybe even likable. The typical distortions created by processing is up to the 20% order of magnitude, and its as if they surely prefer and are aware of a bonfire of good artifacts in front of them but really don't give a ****e about the candle power of the -60dB artifact. Many of the musos I have known do like tube gear because of the gooey sloppy artifacts produced at gross overload, with some reverb as well... anyone can hear them when they're only 30dB below perception. I'll remind you that half a century ago -30dB was considered near enough perfection... Arny Krueger says in another post that it is easy to set up a test of whether people can hear 1mV IM; actually I found it very frustrating getting qualified listeners, which is why in the end I concentrated on testing professional musicians. Musicians do not necessarily have any special hearing abilities. What most good musos do have is a superior ability for tuneful playing in key and a sense of rythm. Some will understand the words of opera sung in english where I will still need subtitles, and couldn't hum along in tune to save my life. They are often dyslectic, a bonus for creativity. They tend to live crazier lives like many artists. Their hearing is different to most other ppl, but not superior when it comes to detection of low level sound, and indeed despite their giftedness, but by 40 the tinnitus has set in as badly as it does with many panel beaters or carpenters. If an audience of members of the general population are chosen, Its a good enough choice. and music played using a volt of average levels, its not hard to arrange the NFB around an amp to alter the THD from 1%, -40dB to 0.1% -60dB, or to 0.01%, -80dB. A friend has a VAC amp with 4 x 300B and one can adjust the global NFB from zero to 9dB applied, and I hear not the slightest difference. Artifacts would perhaps be above the -60dB level with or without NFB.... The VAC PP amp does sound very healthy and clean, and right... You listen to your speakers, not your amp; I would really advise you, unless you are married to these insensitive speakers, first to get good sensitive speakers you can live with forever, then build an amp to suit them. If you have the space, an inexpensive sensitive speaker you can build easily is The Impresario on my netsite, url under my sig. EL84 are particularly sweet in triode but of course pitifully underpowered for insensitive speakers. I have good enough speakers to make differences in source material or amplifiers to be heard. I quite like UL EL84 good for 12 watts AB. But you do need sensitive speakers over 92dB/W/M. Of the common tubes, EL84 and EL34 are the greatest ever made, in my humble opinion. They sure are good in triode, I will give you that. I'd prefer an SE 300B amp though.... Nah, not for a first amp; too expensive for messing around. I think Dave has already made the choice in the SEntry. Agreed, nearly everyone is NOT drawn to using one lone 300B instead of a pair of EL84 in class A. Cost and specialo tranny requirements put the 300B into an untouchable class for many tight arsed DIYers with limited skills. Little do they know that a truly superb PP amp can be made using a pair of 300B for class AB PO = about 28 watts. Patrick Turner. Patrick Turner. Andre Jute Visit Jute on Amps athttp://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 |
#46
Posted to rec.audio.tubes
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pentode amplifiers
Arny Krueger wrote: "John Byrns" wrote in message ... In article , "Arny Krueger" wrote: "Dave" wrote in message news:CfGWi.1359$8S5.242@edtnps82... "Andre Jute" wrote in message ups.com... I know for a fact that people cannot hear as much as 3/4 per cent second harmonic but can hear that much odd harmonic very clearly, and many people can hear or are made uncomfortable by 0.3 per cent odd harmonics. This order of harmonics issue is way overblown. Doesn't matter whether it is odd or even order nonlinearity, it all makes IM. IM is generally aharmonic and it all sounds bad. But even order IM is much more obvious and annoying in listening tests, although I suppose others may find odd order IM more annoying, its probably partly a matter of personal preference. I've never seen that. Got a reference? Here's what my analysis says: Fundamentals: F1 and F2 Second Order IM: F1±F2, F2-F1 Third Order IM: 2F1±F2, 2F2±F1 Fourth Order IM: 2F1±2F2, 2F2±2F1 Fifth Order IM: 3F1±2F2, 3F2±2F1 Almost all sums and differences are inharmonic and therefore likely to be objectionable. Are not the IMD products somewhat different between an amp with nearly all 2H THD as opposed to one with mainly 3H THD? And then there is ordinary real music from instruments. Presumably a fair amount of IMD is included. And then the levels have to be considered. If the THD is low, so is IMD and as the order of IMD products become higher, their levels get lower and lower..... So you need to list the conditions and levels of a REAL amp in a REAL world listening experience before the above "reference" becomes meaningful. Patrick Turner. |
#47
Posted to rec.audio.tubes
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pentode amplifiers
On Nov 4, 3:32 am, Andre Jute wrote:
Jute: Casey: One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to Multi-grid: hey-Hey!!!, What you describe is one of the methods to do DC current cancelling. The other half of the PP primary is straightforward to implement, it takes the same current as the tube idling opposite it. Okay, but wasteful. One can also use heater current. Best SE amp I ever heard was a 50W monster that had a piddling little output TX. Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. cheers, Douglas It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute - Show quoted text - Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas |
#48
Posted to rec.audio.tubes,uk.rec.audio
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Who is useful for listening tests? was pentode amplifiers
On Nov 4, 6:52 am, Patrick Turner wrote:
Musicians do not necessarily have any special hearing abilities. Yes, they do: they have trained perception. They listen consciously. Non-audiophiles from the general population cannot even hear the difference between a boombox played through good speakers and a Class A PP tube amp played through the same speakers. To them it is all "nice", useless for tests. If I could find enough experienced audiophiles -- defined as having trained their own aural perception -- available on a regular basis, I would use them instead. it was just easier in my particular circumstances to find as many classical musicians as required. It should also be observed that most audiophiles talk big about their golden ears but in blind tests have poor discrimination, so that you first require tests to sort out the good listeners. That shocked me; for a while I wondered if the meterheads weren't right, if vanishing THD numbers aren't the holy grail after all... But you don't want to hear about the anguish of an open mind. For the innocent: The point of listening tests isn't to discover which amp or topology is "better": I already know from comparison with years in the concert halls which kinds of amps and which topologies I prefer (Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET with horns). The point of tests is to determine why these topologies affect the emotions differently; psycho-acoustics is probably the last frontier in audio-electronics. Andre Jute "I was at a board meeting for the LA Chapter of the Audio Engineering Society last night on XM Satellite radio audio and data transmission. Sadly, we missed you there, and at the SMPTE and Acoustical Society recent meetings as well. Everyone was asking, 'Where is that wonderful Andre Jute? The world just doesn't rotate without him...'" -- John Mayberry, Emmaco |
#49
Posted to rec.audio.tubes
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The Duggled Method of using PP OPT to give SE outpur was pentode amplifiers
On Nov 4, 12:02 pm, Multi-grid wrote:
On Nov 4, 3:32 am, Andre Jute wrote: Jute: Casey: One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to Multi-grid: hey-Hey!!!, What you describe is one of the methods to do DC current cancelling. The other half of the PP primary is straightforward to implement, it takes the same current as the tube idling opposite it. Okay, but wasteful. One can also use heater current. Best SE amp I ever heard was a 50W monster that had a piddling little output TX. Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. cheers, Douglas It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute - Show quoted text - Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas Sure, standard stuff, but that's not my question. That is about quiescent plate current. I want you to show me how this works: Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. They're your words and they don't make sense to me. Take all the space you need. Please feel free to treat me as a total ignoramus and explain in words of one syllable, with all the tees crossed and all the eyes dotted so that there can be no misunderstanding. A schematic is always good to avoid misunderstanding. 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 |
#50
Posted to rec.audio.tubes
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pentode amplifiers
Dave wrote: "Andre Jute" wrote in message ups.com... Note that you need single-ended transformers, not push-pull. Would a push-pull present only half the impedence to the tube? I.e. a pp is sort of like two transformers in one? Yes, there are virtually two SE OPTs which are tied together tightly with magnetic coupling. One could make a PP amp with two SE amps, with secondaries of the two transfromers in parallel, but different phase, and with grid signals of opposite phase.... But its only really good for class A operation. Patrick Turner. |
#51
Posted to rec.audio.tubes
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pentode amplifiers
Andre Jute wrote: On Nov 2, 11:17 pm, Eeyore wrote: Andre Jute wrote: "Arny Krueger" wrote: "Andre Jute" wrote in message That's true, of course, but I think some, who were educated in silicon only as Dave was, come to tube amps with a silicon mindset that NFB is the cure-all, that if a little is good, more must be better, and lots will be superb. Spoken like someone who lacks experience with how coursed in feedback is taught. Courses in feedback are rarely if ever couched in either terms of either SS or tubes. You're wanking, Krueger. By the time Dave was educated, there were no more tubes. -- AJ Irrelevant to feedback theory. Feedback works in the same way, whatever active parts are in use. It is, after all, merely maths at the end of the day. Graham You two soundbite mentalities have missed the point altogether. Again. The principles of negative feedback are just math, sure. But electronics engineers who are taught to apply negative feedback are now differently instructed to the time when tubes were dominant. For instance, Julian L. Bernstein, Associate Dean of the RCA Day Schools, in his book Audio Systems makes the point that NFB must be used with restraint. By contrast, modern EEs are taught that mo' neg' is betta neg' or what whatever the current street-talk-derived vernacular is on campus this week. You two superannuates are just too old and disconnected and unhip to discover this for yourselves. I made exactly two phone calls to find out all of that. Andre Jute Mr Street Cred One of the "ultimate" and "cutting edge" amplifiers is designed by Halcro of Sth Australia, and boasts 0.0001% thd at 199 watts right up to 20kHz with class AB mosfets in the amp. They think more NFB is best. The HK audio club said of the Halcro gear when it was demonstrated, " Ah, Halcro, it like 300B, but just go louder...." Something tells me the HK audio club members probably got all the music they could ever wish for from a 300B, and frankly, a Halcro was a waste of time and a terrible huge expense. Never did almost nothing cost so much, ie, low THD cost heaps. How the HK club members mention Halcro and a 300B in the same sentence with such inscrutability must have raised weary eyebrows in the Halcro CEO office... Anyway, one can happily leave two noughts out of Halcros THD figures, ie, reduce the NFB enormously, and hear utterly no change whatsoever. But probably that wouldn't make the amps any cheaper. Patrick Turner. |
#52
Posted to rec.audio.tubes
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pentode amplifiers
robert casey wrote: If you mean can you use one half of a PP output transformer for SE, the answer is most definitely no. An SE transfomer is distinguished from a PP one by an air gap. There is a way to use a transformer without an airgap for SE; it is called parafeed, to indicate that the B+ is shunted in parallel to the transformer primary, so that the output doesn't carry the current and can therefore be designed to a more relaxed specificaiton. You also need a big blocking cap, which some say is out of the signal and some say can be heard; you make your choice and take your chances. One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to the effort to build a power supply to supply that and the tube's side. So nobody ever does that, except maybe only if someone has on hand some P-P output transformers but insists on single endedness. But it would be a kludge... :-) Or regap that transformer, but you could ruin the sound quality that was designed into it (I'm not familiar with transformer design, but I've since learned not to waste time fooling with power transformers in audio output work :-) ). You could use the old centertap as a kind of UL tap, but the tap position is not optimal for UL work. But you'd be best off saving the P-P transformers for another project, and get single ended transformers that were designed for that service instead. Trying to convert a PP OPT for SE use with current sources applied to taps, ends is a pile of BS. Its doable, but why oh why? If an ungapped PP OPT is to be used for an SE tube, then it is best done using a parallel feed system where you have a choke of high inductance and gapped ideally so the inductance does not cause a 3 dB loss of gain above 20Hz. Then one end of the PP OPT primary grounded, and the other taken via about 40uF to the tube anode. There is then no dc in the OPT, and no need for a gap. No insulation problems either. Trouble could be when NFB is used though because the extra cap coupling from anode to OPT with its L shunting RL will give an ultimate 180 degree phase shift at very low F. Therefore, the use of NFB from tube anode back to previous stages should be explored. Patrick Turner. |
#53
Posted to rec.audio.tubes
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pentode amplifiers
In article ,
Patrick Turner wrote: John Byrns wrote: In article CfGWi.1359$8S5.242@edtnps82, "Dave" wrote: "Andre Jute" wrote in message ups.com... And NFB up the kazoo. 0.1 per cent is a figure commonly bandied about but I'm not overly impressed. I know for a fact that people cannot hear as much as 3/4 per cent second harmonic but can hear that much odd harmonic very clearly, and many people can hear or are made uncomfortable by 0.3 per cent odd harmonics. What you want to do is not to measure at full power but at some lower power where you will actually use the amp; 1W or 2.83V into 8ohm is a common level with even semi-sensitive speakers. So... is ALL negative feedback bad? I am 40 with some background in electrical engineering and learned nothing but transistor theory at school... thermal runaway pretty much mandates feedback in all transistor amps. There are typically two different feedback mechanisms at work in a transistor amplifier. The first, which is the one you are referring to stabilizes the DC bias, or operating point, of the transistors to prevent thermal runaway as you describe, and also to insure that the "crossover" region of the transfer characteristic has the desired degree of overlap. The second is the overall loop NFB, which is what Andre is talking about, and is used to reduce the audio frequency distortion and noise produced in the amplifier, as well as to stabilize the gain of the amplifier, as the gain of discrete transistors is notoriously inconsistent from sample to sample. You left out one other very important common NFB loop. This is the connection of the output transistors as emitter followers, reducing the gain of the output stage to nearly 1.0. This is often an amount of local series voltage NFB = about 40dB. I actually thought of mentioning that in my post, but I decided to drop it to keep the focus on the subjects of loop NFB and "thermal runaway" which the earlier poster was talking about. I feel it's better to keep threads more focused and not branch out too much unnecessarily. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#54
Posted to rec.audio.tubes
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The Duggled Method of using PP OPT to give SE outpur was pentode amplifiers
In article . com,
Andre Jute wrote: On Nov 4, 12:02 pm, Multi-grid wrote: On Nov 4, 3:32 am, Andre Jute wrote: Jute: Casey: One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to Multi-grid: hey-Hey!!!, What you describe is one of the methods to do DC current cancelling. The other half of the PP primary is straightforward to implement, it takes the same current as the tube idling opposite it. Okay, but wasteful. One can also use heater current. Best SE amp I ever heard was a 50W monster that had a piddling little output TX. Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. cheers, Douglas It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute - Show quoted text - Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas Sure, standard stuff, but that's not my question. That is about quiescent plate current. I want you to show me how this works: Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. They're your words and they don't make sense to me. Take all the space you need. Please feel free to treat me as a total ignoramus and explain in words of one syllable, with all the tees crossed and all the eyes dotted so that there can be no misunderstanding. A schematic is always good to avoid misunderstanding. Andre, you are wasting your time with Multi-grid, you won't get any answers from him as he hasn't yet reached the point in his studies where he can even understand the question. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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The Duggled Method of using PP OPT to give SE outpur was pentode amplifiers
On Nov 4, 3:52 pm, John Byrns wrote:
In article . com, Andre Jute wrote: On Nov 4, 12:02 pm, Multi-grid wrote: On Nov 4, 3:32 am, Andre Jute wrote: Jute: Casey: One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to Multi-grid: hey-Hey!!!, What you describe is one of the methods to do DC current cancelling. The other half of the PP primary is straightforward to implement, it takes the same current as the tube idling opposite it. Okay, but wasteful. One can also use heater current. Best SE amp I ever heard was a 50W monster that had a piddling little output TX. Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. cheers, Douglas It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute - Show quoted text - Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas Sure, standard stuff, but that's not my question. That is about quiescent plate current. I want you to show me how this works: Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. They're your words and they don't make sense to me. Take all the space you need. Please feel free to treat me as a total ignoramus and explain in words of one syllable, with all the tees crossed and all the eyes dotted so that there can be no misunderstanding. A schematic is always good to avoid misunderstanding. Andre, you are wasting your time with Multi-grid, you won't get any answers from him as he hasn't yet reached the point in his studies where he can even understand the question. Yes, I suspected that. That is why I call it the "Duggled Method" to indicate I think Dougles Muti-grid is sucking on a hind tit he hasn't properly grasped. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ Still, wouldn't it be a fabulous invention to make the filament current do something else as well? Andre Jute "I was at a board meeting for the LA Chapter of the Audio Engineering Society last night on XM Satellite radio audio and data transmission. Sadly, we missed you there, and at the SMPTE and Acoustical Society recent meetings as well. Everyone was asking, 'Where is that wonderful Andre Jute? The world just doesn't rotate without him...'" -- John Mayberry, Emmaco |
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Who is useful for listening tests? was pentode amplifiers
Andre Jute wrote: Patrick Turner wrote: Musicians do not necessarily have any special hearing abilities. Yes, they do: they have trained perception. They listen consciously. Non-audiophiles from the general population cannot even hear the difference between a boombox played through good speakers and a Class A PP tube amp played through the same speakers. To them it is all "nice", useless for tests. The same holds true for plenty of musicians too. The idea that ALL musicians have wonderfully critical hearing is just plain wrong. And those that do have good critical hearing may not be listening for the audible cues a technical person will be. Graham |
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pentode amplifiers
On Nov 4, 2:52 pm, Patrick Turner wrote:
Dave wrote: "Andre Jute" wrote in message oups.com... Note that you need single-ended transformers, not push-pull. Would a push-pull present only half the impedence to the tube? I.e. a pp is sort of like two transformers in one? Yes, there are virtually two SE OPTs which are tied together tightly with magnetic coupling. One could make a PP amp with two SE amps, with secondaries of the two transfromers in parallel, but different phase, and with grid signals of opposite phase.... But its only really good for class A operation. Patrick Turner. Careful, Patrick. I think Dave's question is practical, of the "can I do this" kind, rather than theoretical. Your answer to Robert Casey's suggestion is more to the point. -- Andre Jute |
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pentode amplifiers
On Nov 4, 3:03 pm, Patrick Turner wrote:
Andre Jute wrote: On Nov 2, 11:17 pm, Eeyore wrote: Andre Jute wrote: "Arny Krueger" wrote: "Andre Jute" wrote in message That's true, of course, but I think some, who were educated in silicon only as Dave was, come to tube amps with a silicon mindset that NFB is the cure-all, that if a little is good, more must be better, and lots will be superb. Spoken like someone who lacks experience with how coursed in feedback is taught. Courses in feedback are rarely if ever couched in either terms of either SS or tubes. You're wanking, Krueger. By the time Dave was educated, there were no more tubes. -- AJ Irrelevant to feedback theory. Feedback works in the same way, whatever active parts are in use. It is, after all, merely maths at the end of the day. Graham You two soundbite mentalities have missed the point altogether. Again. The principles of negative feedback are just math, sure. But electronics engineers who are taught to apply negative feedback are now differently instructed to the time when tubes were dominant. For instance, Julian L. Bernstein, Associate Dean of the RCA Day Schools, in his book Audio Systems makes the point that NFB must be used with restraint. By contrast, modern EEs are taught that mo' neg' is betta neg' or what whatever the current street-talk-derived vernacular is on campus this week. You two superannuates are just too old and disconnected and unhip to discover this for yourselves. I made exactly two phone calls to find out all of that. Andre Jute Mr Street Cred One of the "ultimate" and "cutting edge" amplifiers is designed by Halcro of Sth Australia, and boasts 0.0001% thd at 199 watts right up to 20kHz with class AB mosfets in the amp. They think more NFB is best. The HK audio club said of the Halcro gear when it was demonstrated, " Ah, Halcro, it like 300B, but just go louder...." Something tells me the HK audio club members probably got all the music they could ever wish for from a 300B, and frankly, a Halcro was a waste of time and a terrible huge expense. They didn't want to say anything negative because the PR dolly from Halcro was so nice... Never did almost nothing cost so much, ie, low THD cost heaps. How the HK club members mention Halcro and a 300B in the same sentence with such inscrutability must have raised weary eyebrows in the Halcro CEO office... Anyway, one can happily leave two noughts out of Halcros THD figures, ie, reduce the NFB enormously, and hear utterly no change whatsoever. But probably that wouldn't make the amps any cheaper. Patrick Turner. I was going to reply to your claim that you can't hear any difference between ZNFB and 9dB but can't now find the message in which you said it in the ferment of messages on RAT -- who said RAT is dying? what a fool! This is as good a place as any. I'm not surprised at all by your number. Less than ten years ago Bill May, my late technical guy, conducted careful blind tests and determined that I could tell GNFB as low as 6dB. When I did the tests on him, and he had good ears but was pushing 70, he couldn't hear GNFB until 12dB. This was on a standard design of trioded PP Class A amp (input, splitter, driver, power stages). On simpler amps the GNFB could be heard a dB or two lower, but very design dependent even when within the level of statistical confidence. A hard and fast rule to answer Dave's earlier question -- how much distortion is permissable? -- is so difficult to answer, once you are below the crude direct perception level, precisely because the *aural* effects of the NFB required to lower the harmonics are not linearly predictable. 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 |
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Who is useful for listening tests? was pentode amplifiers
Andre Jute wrote: On Nov 4, 6:52 am, Patrick Turner wrote: Musicians do not necessarily have any special hearing abilities. Yes, they do: they have trained perception. They listen consciously. Non-audiophiles from the general population cannot even hear the difference between a boombox played through good speakers and a Class A PP tube amp played through the same speakers. To them it is all "nice", useless for tests. Jeezzuuus! More than half the musos I know are dumb****s. A few might have benefitted from being trained musically, but the majority are not. The majority are self taught rock/jaz musos, and only a real minority score well in music reproduction examination tests. If I could find enough experienced audiophiles -- defined as having trained their own aural perception -- available on a regular basis, I would use them instead. it was just easier in my particular circumstances to find as many classical musicians as required. The serious audio clubs in Australia such as the Melbourne Audio Club, MAC, and Audiophile Society of NSW, ASON contain enough practised and experienced ppl whose opinion can be considered seriously when testing AB set ups in front of them. I was a member of ASON for some years and demoed my gear several times and AB'd it in "sound offs" to see what sounded better. The results embarrassed the guy who believed in triodes with no GNFB. It should also be observed that most audiophiles talk big about their golden ears but in blind tests have poor discrimination, so that you first require tests to sort out the good listeners. Yes, but there were enough good ears in the club to get as good an idea about the audio quality as you'd ever want. That shocked me; for a while I wondered if the meterheads weren't right, if vanishing THD numbers aren't the holy grail after all... But you don't want to hear about the anguish of an open mind. ASON club members did not hear anything special with gear that had 10 times or lower measured THD/IMD than the tube gear I demoed. About 1/2 used SS, 1/2 used tube gear. Speakers varied from horns, generally HQ dynamics, and some ESL. Sources of the club were also better than average. For the innocent: The point of listening tests isn't to discover which amp or topology is "better": I already know from comparison with years in the concert halls which kinds of amps and which topologies I prefer (Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET with horns). The point of tests is to determine why these topologies affect the emotions differently; psycho-acoustics is probably the last frontier in audio-electronics. Better usually means sounds better to audiophiles, many of whom couldn't care a hoot about the measurements. Better to an engineer means it measures better, and engineers often are dull emotionally, and incapable of listening to music at all. A 100 times betterment in measurements usually does NOT give a 100 time betterment in sound quality. Patrick Turner. Andre Jute "I was at a board meeting for the LA Chapter of the Audio Engineering Society last night on XM Satellite radio audio and data transmission. Sadly, we missed you there, and at the SMPTE and Acoustical Society recent meetings as well. Everyone was asking, 'Where is that wonderful Andre Jute? The world just doesn't rotate without him...'" -- John Mayberry, Emmaco |
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pentode amplifiers
Jute:
If you mean can you use one half of a PP output transformer for SE, the answer is most definitely no. An SE transfomer is distinguished from a PP one by an air gap. There is a way to use a transformer without an airgap for SE; it is called parafeed, to indicate that the B+ is shunted in parallel to the transformer primary, so that the output doesn't carry the current and can therefore be designed to a more relaxed specificaiton. You also need a big blocking cap, which some say is out of the signal and some say can be heard; you make your choice and take your chances. Casey: One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to the effort to build a power supply to supply that and the tube's side. So nobody ever does that, except maybe only if someone has on hand some P-P output transformers but insists on single endedness. But it would be a kludge... :-) Or regap that transformer, but you could ruin the sound quality that was designed into it (I'm not familiar with transformer design, but I've since learned not to waste time fooling with power transformers in audio output work :-) ). You could use the old centertap as a kind of UL tap, but the tap position is not optimal for UL work. But you'd be best off saving the P-P transformers for another project, and get single ended transformers that were designed for that service instead. Turner: Trying to convert a PP OPT for SE use with current sources applied to taps, ends is a pile of BS. Its doable, but why oh why? If an ungapped PP OPT is to be used for an SE tube, then it is best done using a parallel feed system where you have a choke of high inductance and gapped ideally so the inductance does not cause a 3 dB loss of gain above 20Hz. Then one end of the PP OPT primary grounded, and the other taken via about 40uF to the tube anode. There is then no dc in the OPT, and no need for a gap. No insulation problems either. Trouble could be when NFB is used though because the extra cap coupling from anode to OPT with its L shunting RL will give an ultimate 180 degree phase shift at very low F. Therefore, the use of NFB from tube anode back to previous stages should be explored. Patrick Turner. It has always seemed to me a parafeed amplifier is a kludge to gimmick a heathrobinson created by false reasoning. To save the cost of an SE transformer and permit the use of a PP transformer in SE, the parafeeder then has to buy a choke and a cap and a larger chassis... Andre Jute Last of the big spenders |
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Who is useful for listening tests? was pentode amplifiers
On Nov 4, 4:41 pm, Eeyore
wrote: Andre Jute wrote: Patrick Turner wrote: Musicians do not necessarily have any special hearing abilities. Yes, they do: they have trained perception. They listen consciously. Non-audiophiles from the general population cannot even hear the difference between a boombox played through good speakers and a Class A PP tube amp played through the same speakers. To them it is all "nice", useless for tests. The same holds true for plenty of musicians too. The idea that ALL musicians have wonderfully critical hearing is just plain wrong. What is your problem, Poopie? Where did I say I was talking about "ALL musicians". Why don't you learn to read? I specifically said, in the section of my post you stupidly snipped: "it was just easier in my particular circumstances to find as many classical musicians as required." And those that do have good critical hearing may not be listening for the audible cues a technical person will be. You're a moron, Poopie. Where did I say anything about "technical persons"? In fact, I specified psycho-acoustic reasons in the part of my post you stupidly snipped: "For the innocent: The point of listening tests isn't to discover which amp or topology is "better": I already know from comparison with years in the concert halls which kinds of amps and which topologies I prefer (Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET with horns). The point of tests is to determine why these topologies affect the emotions differently; psycho-acoustics is probably the last frontier in audio-electronics." Graham If you attention span is shorter than your dick, Poopie, stay out of my threads. They aren't suitable for soundbiters and idiots. Andre Jute "I was at a board meeting for the LA Chapter of the Audio Engineering Society last night on XM Satellite radio audio and data transmission. Sadly, we missed you there, and at the SMPTE and Acoustical Society recent meetings as well. Everyone was asking, 'Where is that wonderful Andre Jute? The world just doesn't rotate without him...'" -- John Mayberry, Emmaco |
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Who is useful for listening tests? was pentode amplifiers
On Nov 4, 5:09 pm, Patrick Turner wrote:
Andre Jute wrote: On Nov 4, 6:52 am, Patrick Turner wrote: Musicians do not necessarily have any special hearing abilities. Yes, they do: they have trained perception. They listen consciously. Non-audiophiles from the general population cannot even hear the difference between a boombox played through good speakers and a Class A PP tube amp played through the same speakers. To them it is all "nice", useless for tests. Jeezzuuus! More than half the musos I know are dumb****s. Of course they are. They play jazz which is by definition not music or have deafened themselves with amplified guitars. You want to acquaint yourself with a better class of musician. A few might have benefitted from being trained musically, but the majority are not. All of those in my listening groups had at least ten years of formal musical training, many or even most since they first started started school or even before. The majority are self taught rock/jaz musos, and only a real minority score well in music reproduction examination tests. Yech. These are not musicians, Patrick, they are makers of noise. If I could find enough experienced audiophiles -- defined as having trained their own aural perception -- available on a regular basis, I would use them instead. it was just easier in my particular circumstances to find as many classical musicians as required. The serious audio clubs in Australia such as the Melbourne Audio Club, MAC, and Audiophile Society of NSW, ASON contain enough practised and experienced ppl whose opinion can be considered seriously when testing AB set ups in front of them. I was a member of ASON for some years and demoed my gear several times and AB'd it in "sound offs" to see what sounded better. You're lucky. The local Gramophone Club, the night I went, played old records on scratchy equipment; they are not audiophiles but music lovers. Good for them, I say, but useless for my purposes. The results embarrassed the guy who believed in triodes with no GNFB. It should also be observed that most audiophiles talk big about their golden ears but in blind tests have poor discrimination, so that you first require tests to sort out the good listeners. Yes, but there were enough good ears in the club to get as good an idea about the audio quality as you'd ever want. Melbourne, just by itself, has more people in it than all of Ireland. It is a lot easier to put together experienced audiophiles there than here. That shocked me; for a while I wondered if the meterheads weren't right, if vanishing THD numbers aren't the holy grail after all... But you don't want to hear about the anguish of an open mind. ASON club members did not hear anything special with gear that had 10 times or lower measured THD/IMD than the tube gear I demoed. About 1/2 used SS, 1/2 used tube gear. Speakers varied from horns, generally HQ dynamics, and some ESL. Sources of the club were also better than average. And there you have it: serious people, serious gear, experienced ears. For the innocent: The point of listening tests isn't to discover which amp or topology is "better": I already know from comparison with years in the concert halls which kinds of amps and which topologies I prefer (Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET with horns). The point of tests is to determine why these topologies affect the emotions differently; psycho-acoustics is probably the last frontier in audio-electronics. Better usually means sounds better to audiophiles, many of whom couldn't care a hoot about the measurements. Better to an engineer means it measures better, and engineers often are dull emotionally, and incapable of listening to music at all. "Engineers" aren't my problem, except when they're dumb enough to think they can tell me my business. I'm interested in the sources of emotion. Or, as an assistant at one test told a panel member, "Andre is after the effect of the affect." Poor fellow thought the pretty bird was swearing at him! A 100 times betterment in measurements usually does NOT give a 100 time betterment in sound quality. Gee, now you tell me, after I wasted my youth chasing AC balance... 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 |
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pentode amplifiers
It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas As for using that current to run heaters, I could see someone selecting a version of the desired output tube that draws heater current the same as the desired quiescent cancellation current. There's the 7695, just like the 7754 except for heater current of 150ma at 50V. It wants 1100 ohm load resistance, but with plate voltage of 130VDC, that tube isn't real exciting. But there are other tubes with high heater voltages out there. BUt what one would do is series string the output tube heater with its various preamp and driver tube heaters, and pad the shortfall of heater voltage total with a power resistor. But that resistance would look like a load to the output tube. |
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pentode amplifiers
robert casey wrote:
It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas As for using that current to run heaters, I could see someone selecting a version of the desired output tube that draws heater current the same as the desired quiescent cancellation current. There's the 7695, just like the 7754 except for heater current of 150ma at 50V. It wants 1100 ohm load resistance, but with plate voltage of 130VDC, that tube isn't real exciting. But there are other tubes with high heater voltages out there. BUt what one would do is series string the output tube heater with its various preamp and driver tube heaters, and pad the shortfall of heater voltage total with a power resistor. But that resistance would look like a load to the output tube. And by transformer action, the top of the heater string will carry the same AC voltage as the OP anode. So the heater-string resistance will be an unproductive load in parallel with the speaker (as referred to the OPT primary). If your heaters pull 150mA, a 350V HT means a string resistance of 2.3kR. In parallel with a reflected load impedance of several kR, it will eat the lion's share of the OP watts. OK, while we're on zany ideas, here's another. Have someone wind a PP transformer, with the two primary halves isolated. Now connect the "starts" of each winding together, and call that the "centre". So the free ends would see voltage in phase with each other. Connect the "centre tap" to a big cap. to ground, the OP anode to one end, and the other end via a large choke to HT+. Now the DC components in the two halves cancel, as required. Of course, this is topologically very similar to a parafeed, but we have eliminated that huge OP capacitor. Ah well, I did say it was zany... |
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pentode amplifiers
robert casey wrote:
It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas As for using that current to run heaters, I could see someone selecting a version of the desired output tube that draws heater current the same as the desired quiescent cancellation current. There's the 7695, just like the 7754 except for heater current of 150ma at 50V. It wants 1100 ohm load resistance, but with plate voltage of 130VDC, that tube isn't real exciting. But there are other tubes with high heater voltages out there. BUt what one would do is series string the output tube heater with its various preamp and driver tube heaters, and pad the shortfall of heater voltage total with a power resistor. But that resistance would look like a load to the output tube. Sure thing, Robert, the series string of heater voltages is vintage table radio practice. I had the pleasure of studying that one closely when a couple of weeks ago I redrew John Byrns's "Amplifier without Power Transformer". I can see how that is a useful topology which can double as a bleeder for the caps. But I was looking for some really major advance here, as Douglas Multi-grid first appeared to offer, some new, stunning way of using the same current as drives the filaments to make a PP transformer usable as an SE transformer. The truth is that, above a tiny fraction of the PP current, I have as little faith in PP trx used for SE as Patrick has. Using PP trannies for SE is really just a novelty for a gee-whiz a a snowed-in prototype, not a serious possibility for a permanent amp. Andre Jute "I was at a board meeting for the LA Chapter of the Audio Engineering Society last night on XM Satellite radio audio and data transmission. Sadly, we missed you there, and at the SMPTE and Acoustical Society recent meetings as well. Everyone was asking, 'Where is that wonderful Andre Jute? The world just doesn't rotate without him...'" -- John Mayberry, Emmaco |
#66
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pentode amplifiers
In article ,
robert casey wrote: It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas As for using that current to run heaters, I could see someone selecting a version of the desired output tube that draws heater current the same as the desired quiescent cancellation current. There's the 7695, just like the 7754 except for heater current of 150ma at 50V. It wants 1100 ohm load resistance, but with plate voltage of 130VDC, that tube isn't real exciting. But there are other tubes with high heater voltages out there. BUt what one would do is series string the output tube heater with its various preamp and driver tube heaters, and pad the shortfall of heater voltage total with a power resistor. But that resistance would look like a load to the output tube. That's why you need to add an inductor in series with the "resistance" so that it doesn't load the output tube. However at that point, since you have to pay for the choke, you might as well go with a parafeed connection to keep the DC out of the output transformer, and also reap the other benefits of that arrangement. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#67
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pentode amplifiers
In article
, David R Brooks wrote: robert casey wrote: It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas As for using that current to run heaters, I could see someone selecting a version of the desired output tube that draws heater current the same as the desired quiescent cancellation current. There's the 7695, just like the 7754 except for heater current of 150ma at 50V. It wants 1100 ohm load resistance, but with plate voltage of 130VDC, that tube isn't real exciting. But there are other tubes with high heater voltages out there. BUt what one would do is series string the output tube heater with its various preamp and driver tube heaters, and pad the shortfall of heater voltage total with a power resistor. But that resistance would look like a load to the output tube. And by transformer action, the top of the heater string will carry the same AC voltage as the OP anode. So the heater-string resistance will be an unproductive load in parallel with the speaker (as referred to the OPT primary). If your heaters pull 150mA, a 350V HT means a string resistance of 2.3kR. In parallel with a reflected load impedance of several kR, it will eat the lion's share of the OP watts. OK, while we're on zany ideas, here's another. Have someone wind a PP transformer, with the two primary halves isolated. Now connect the "starts" of each winding together, and call that the "centre". So the free ends would see voltage in phase with each other. Connect the "centre tap" to a big cap. to ground, the OP anode to one end, and the other end via a large choke to HT+. Now the DC components in the two halves cancel, as required. Of course, this is topologically very similar to a parafeed, but we have eliminated that huge OP capacitor. Ah well, I did say it was zany... Why bother having a special transformer wound, especially since the whole idea is probably to use an existing PP transformer, your zany idea should work just as well with a standard wound PP transformer? However once you have to pay for the "large choke", you might as well bite the bullet and pop for the parafeed capacitor too, and use the actual parafeed connection which gives improved power supply rejection, reducing the hum level at the speaker. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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Who is useful for listening tests? was pentode amplifiers
"Andre Jute" wrote in message oups.com... On Nov 4, 6:52 am, Patrick Turner wrote: Musicians do not necessarily have any special hearing abilities. They are also not immune to hearing damage, even occupationally-related. Yes, they do: they have trained perception. But they are not unique in that regard. Also, what they listen for is not necessarily the same as what you listen for when you listen for differences between audio products. They listen consciously. That's hardly unique to musicians. Non-audiophiles from the general population cannot even hear the difference between a boombox played through good speakers and a Class A PP tube amp played through the same speakers. Boomboxes rarely if ever have speaker outputs, so this is a nonsense statement. To them it is all "nice", useless for tests. I've done enough listening tests with non-audiophiles and non-musicans to be careful about putting them all down. If I could find enough experienced audiophiles -- defined as having trained their own aural perception -- available on a regular basis, I would use them instead. Been there done that. BTW, one good way for audiophiles to train their perceptions is to spend some time actually listening for differences that are known to be audible, but perhaps neer the margin of audibility. it was just easier in my particular circumstances to find as many classical musicians as required. I've definately worked with classical musicans with serious ear damage. While they generally have good acuity when it comes to tone and timing, there's a lot that goes wrong in audio that is independent of that. It should also be observed that most audiophiles talk big about their golden ears but in blind tests have poor discrimination, so that you first require tests to sort out the good listeners. It is true that the high end audio industry pretty much trains audiophiles to have a very optimistic view of their hearing acuity. That shocked me; for a while I wondered if the meterheads weren't right, if vanishing THD numbers aren't the holy grail after all... But you don't want to hear about the anguish of an open mind. No danger of hearing about the anguish of an open mind from Jute, his sockpuppets, and his fellow-travelers. For the innocent: The point of listening tests isn't to discover which amp or topology is "better": I already know from comparison with years in the concert halls which kinds of amps and which topologies I prefer (Class A1 triodes or trioded pentodes in PP with ESL, and ditto in SET with horns). Thanks for admitting that you already know the right answers, Jute. The point of tests is to determine why these topologies affect the emotions differently; psycho-acoustics is probably the last frontier in audio-electronics. So far I have yet to see a credible statement about psychoacoustics from you, Jute. Andre Jute "I was at a board meeting for the LA Chapter of the Audio Engineering Society last night on XM Satellite radio audio and data transmission. Sadly, we missed you there, and at the SMPTE and Acoustical Society recent meetings as well. Everyone was asking, 'Where is that wonderful Andre Jute? The world just doesn't rotate without him...'" -- John Mayberry, Emmaco More likely, they were asking why XP used to sound so much better, but now generally sounds like crap. The answer is bandwidth and what happens to audio when you try to route twice as many channels through the same bandwidth. |
#69
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pentode amplifiers
"Andre Jute" wrote in message ups.com... ). Sure. I don't know how you will build it. I have to assume you know enough to ground your chassis! I also assume you will use a three- point (IEC) grounded plug, not those dangerous American two-point things. Isn't there a rationale floating around out there that says that if you mains ground every piece of audio gear, you'll end up with ground loops? Wouldn't tying your signal ground to mains earth potentially amplify any noise on the ground circuit, i.e. hum from your fridge motor and everything else? |
#70
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pentode amplifiers
Dave wrote: "Andre Jute" wrote Sure. I don't know how you will build it. I have to assume you know enough to ground your chassis! I also assume you will use a three- point (IEC) grounded plug, not those dangerous American two-point things. Isn't there a rationale floating around out there that says that if you mains ground every piece of audio gear, you'll end up with ground loops? You mean hum ? Depends on the existence or otherwise of any magnetic fields and leakage currents. Wouldn't tying your signal ground to mains earth potentially amplify any noise on the ground circuit, i.e. hum from your fridge motor and everything else? NO. That simply illustrates a very poor understanding of audio circuits. Graham |
#71
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pentode amplifiers
And by transformer action, the top of the heater string will carry the same AC voltage as the OP anode. So the heater-string resistance will be an unproductive load in parallel with the speaker (as referred to the OPT primary). If your heaters pull 150mA, a 350V HT means a string resistance of 2.3kR. In parallel with a reflected load impedance of several kR, it will eat the lion's share of the OP watts. I suppose one could build a constant current sucker circuit to make it look like a very high impedance on that transformer winding. But at this point (if not already) we're piling so much silliness into this as to be absurd. As well as so much cost as to make it better putting that cost into a real single ended transformer in the first place. |
#72
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The Duggled Method of using PP OPT to give SE outpur was pentode amplifiers
On Nov 4, 4:43 pm, Andre Jute wrote:
On Nov 4, 12:02 pm, Multi-grid wrote: On Nov 4, 3:32 am, Andre Jute wrote: Jute: Casey: One could use a push-pull output transformer om a single-ended design, if you also send a steady DC current (equal to the quiescent class A current of the tube) thru the other half of the primary from the centertap (connected to B+) to the unused side, via most likely a power resistor to ground. But that's rather wasteful of the power you went to Multi-grid: hey-Hey!!!, What you describe is one of the methods to do DC current cancelling. The other half of the PP primary is straightforward to implement, it takes the same current as the tube idling opposite it. Okay, but wasteful. One can also use heater current. Best SE amp I ever heard was a 50W monster that had a piddling little output TX. Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. cheers, Douglas It isn't clear to me at all how "once can use the heater current", presumably for some purpose beyond heating the filaments. Can you please explain more, or provide a reference, or even an outline sketch of connections. Andre Jute - Show quoted text - Well Andre, Do you see how the example using a PP output is using half the primary to cancell DC-generated flux in the core? It takes the same amount of current as is being passed at idle by the tube we're applying signal to. Cheers, Douglas Sure, standard stuff, but that's not my question. That is about quiescent plate current. I want you to show me how this works: Through a special winding went the required 25A of heater current for that valve...no intentional gap needed anymore. They're your words and they don't make sense to me. Take all the space you need. Please feel free to treat me as a total ignoramus and explain in words of one syllable, with all the tees crossed and all the eyes dotted so that there can be no misunderstanding. A schematic is always good to avoid misunderstanding. Andre Jute Visit Jute on Amps athttp://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- Hide quoted text - - Show quoted text - What don't you 'get'? Think some more. Think 'ampere-turns'. Take a primary of two to three thousand turns, and run 100 mA through it. Put this coil around a minimum gap/alternate stacked E-I or cut C-core. What happens to the flux? Got an answer yet? Take another winding, and run the filament current through it. It is substantially larger than 0.1 Ampere( actually 25 A was my example). You should energize the correct end of this winding, eh? Now what is going on? Given a given coil geometry and interleave, which will have more injurious parasitic stuff like interwinding capacitance and leakage L, smaller core or bigger cored designs? and quoted from Mr.Burns: Andre, you are wasting your time with Multi-grid, you won't get any answers from him as he hasn't yet reached the point in his studies where he can even understand the question. Regards, John Byrns Now John, It amazes me that you would actually expect me to answer given your insults and slights. I don't see the need to answer in much detail to folks who claim such deep understanding of tube circuit behaviour and design. Besides, it is more fun for you to figure it out yourself, and less work for me. Behave yourself. There is additional issues with parafeeding PP outputs, they are designed( if any good ) to have the CT at AC ground. Using them SE and full length puts something besides AC ground at the CT, yes? cheers, Douglas |
#73
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pentode amplifiers
"Eeyore" wrote in message ... Dave wrote: "Andre Jute" wrote Sure. I don't know how you will build it. I have to assume you know enough to ground your chassis! I also assume you will use a three- point (IEC) grounded plug, not those dangerous American two-point things. Isn't there a rationale floating around out there that says that if you mains ground every piece of audio gear, you'll end up with ground loops? You mean hum ? Depends on the existence or otherwise of any magnetic fields and leakage currents. Okay, let's suppose for the sake of arguement that there is either AC or DC current on the mains ground. Would you get hum? What might be any other effects? Wouldn't tying your signal ground to mains earth potentially amplify any noise on the ground circuit, i.e. hum from your fridge motor and everything else? NO. That simply illustrates a very poor understanding of audio circuits. Then why do many designers go to the effort of isolating signal ground? Are you saying noise on the mains ground will have no effect on the output? Dave |
#74
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The Duggled Method of using PP OPT to give SE outpur was pentode amplifiers
In article . com,
Multi-grid wrote: On Nov 4, 4:43 pm, Andre Jute wrote: They're your words and they don't make sense to me. Take all the space you need. Please feel free to treat me as a total ignoramus and explain in words of one syllable, with all the tees crossed and all the eyes dotted so that there can be no misunderstanding. A schematic is always good to avoid misunderstanding. What don't you 'get'? Think some more. Think 'ampere-turns'. Take a primary of two to three thousand turns, and run 100 mA through it. Put this coil around a minimum gap/alternate stacked E-I or cut C-core. What happens to the flux? Got an answer yet? Take another winding, and run the filament current through it. It is substantially larger than 0.1 Ampere( actually 25 A was my example). You should energize the correct end of this winding, eh? Andre, notice how Multi-grid is avoiding your question, and being evasive about how this scheme actually works. It is straight forward to use the filament current to provide the bias to the core to offset the current from the amplifier tube, or any other current for that matter, as long as the number of ampere-turns is the same as in the active primary, as Multi-grid points out. Unfortunately the issue that Multi-grid doesn't want to deal with, or can't, is that a substantial portion of the audio power generated by the active tube is dissipated across the filament resistance of the tube and never makes it to the speaker. The bottom line is that this circuit doesn't work very well when built as Multi-grid describes it. The problem can be dealt with, but dealing with it adds considerable extra cost, which makes one wonder why anyone in their right mind would take this approach to building an amplifier in the first place? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
#75
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pentode amplifiers
Dave wrote: "Eeyore" wrote Dave wrote: "Andre Jute" wrote Sure. I don't know how you will build it. I have to assume you know enough to ground your chassis! I also assume you will use a three- point (IEC) grounded plug, not those dangerous American two-point things. Isn't there a rationale floating around out there that says that if you mains ground every piece of audio gear, you'll end up with ground loops? You mean hum ? Depends on the existence or otherwise of any magnetic fields and leakage currents. Okay, let's suppose for the sake of arguement that there is either AC or DC current on the mains ground. First off forget DC. It's very unlikely anyway and won't affect the audio. Next, what do you mean by "there is AC current on the mains ground" ? To be honest it sounds like you don't know what you mean. What does 'on a ground' mean ? 'ON' is the wrong word for a current anyway. You may have current IN a conductor but not ON one. You can however have a voltage ON a conductor. Do you mean that the voltage at the ground connection at the wall socket isn't actually a 'pure' ground ? Would you get hum? What might be any other effects? You'll get hum in a configuration where multiple pieces of audio equipment share BOTH a mains earth AND unbalanced signal interconnects that also use the earth for the low side of the signal **IF** and **only IF** those loops created by the interconnects and mains wiring are subject to an alternating magnetic field OR if any of those pieces of equipment has a leakage current to earth that then flows in the shield/screens of the interconnects instead of flowing ONLY in the ground wire of the mains supply. Other effects would include susceptibility to other tyres of magnetic field such as created by the scan coils of a CRT based TV or PC monitor. Wouldn't tying your signal ground to mains earth potentially amplify any noise on the ground circuit, i.e. hum from your fridge motor and everything else? NO. That simply illustrates a very poor understanding of audio circuits. Then why do many designers go to the effort of isolating signal ground? A lot of it is 'tradition' and a lot of tradition is very bad practice too. You don't see this in professional equipment. Are you saying noise on the mains ground will have no effect on the output? If ALL the equipment is 'riding' on some voltage on the ground/earth connection equally, i.e. it's not a perfect ground it'll still perform just fine. The 'ground' is for the most part simply some reference potential for the purposes of the audio circuitry. As long as EVERYTHING shares that same potential, there will be NO adverse effect. Graham |
#76
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pentode amplifiers
"Eeyore" wrote in message ... Next, what do you mean by "there is AC current on the mains ground" ? To be honest it sounds like you don't know what you mean. What does 'on a ground' mean ? 'ON' is the wrong word for a current anyway. You may have current IN a conductor but not ON one. You can however have a voltage ON a conductor. Do you mean that the voltage at the ground connection at the wall socket isn't actually a 'pure' ground ? What I meant was suppose there was another device on the same circuit (i.e. common ground wiring) which was leaking current INto the ground wiring. But I see what you mean below when you say that it won't matter as long as ALL of the pieces of equipment are aat the same elevated ground potential. Would you get hum? What might be any other effects? You'll get hum in a configuration where multiple pieces of audio equipment share BOTH a mains earth AND unbalanced signal interconnects that also use the earth for the low side of the signal **IF** and **only IF** those loops created by the interconnects and mains wiring are subject to an alternating magnetic field OR if any of those pieces of equipment has a leakage current to earth that then flows in the shield/screens of the interconnects instead of flowing ONLY in the ground wire of the mains supply. Other effects would include susceptibility to other tyres of magnetic field such as created by the scan coils of a CRT based TV or PC monitor. Wouldn't tying your signal ground to mains earth potentially amplify any noise on the ground circuit, i.e. hum from your fridge motor and everything else? NO. That simply illustrates a very poor understanding of audio circuits. Then why do many designers go to the effort of isolating signal ground? A lot of it is 'tradition' and a lot of tradition is very bad practice too. You don't see this in professional equipment. Are you saying noise on the mains ground will have no effect on the output? If ALL the equipment is 'riding' on some voltage on the ground/earth connection equally, i.e. it's not a perfect ground it'll still perform just fine. The 'ground' is for the most part simply some reference potential for the purposes of the audio circuitry. As long as EVERYTHING shares that same potential, there will be NO adverse effect. Thanks. that was clear, concise, and answered my questions fully. At one time I had considered building some balanced XLR adaptors to convert my existing equipment outputs. If I am having no hum issues, is it your opinion that this would be a waste of time, or, as many "serious audiophiles" insist, do the balanced interconnects improve the sound in any way? Dave |
#77
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pentode amplifiers
Dave wrote: "Eeyore" wrote Next, what do you mean by "there is AC current on the mains ground" ? To be honest it sounds like you don't know what you mean. What does 'on a ground' mean ? 'ON' is the wrong word for a current anyway. You may have current IN a conductor but not ON one. You can however have a voltage ON a conductor. Do you mean that the voltage at the ground connection at the wall socket isn't actually a 'pure' ground ? What I meant was suppose there was another device on the same circuit (i.e. common ground wiring) which was leaking current INto the ground wiring. But I see what you mean below when you say that it won't matter as long as ALL of the pieces of equipment are aat the same elevated ground potential. You got it. snip If ALL the equipment is 'riding' on some voltage on the ground/earth connection equally, i.e. it's not a perfect ground it'll still perform just fine. The 'ground' is for the most part simply some reference potential for the purposes of the audio circuitry. As long as EVERYTHING shares that same potential, there will be NO adverse effect. Thanks. that was clear, concise, and answered my questions fully. Thank you. I did try to cover it fully. At one time I had considered building some balanced XLR adaptors to convert my existing equipment outputs. If I am having no hum issues, is it your opinion that this would be a waste of time, or, as many "serious audiophiles" insist, do the balanced interconnects improve the sound in any way? Balanced audio does NOT 'improve the sound' per se. Its main function is to reduce or effectively eliminate equipment interconnecting problems. If you have no such problems, then you don't need to change to balanced connections. Most 'audiophools' haven't a clue btw. They imagine it's magic not science and technology. Graham |
#78
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The Duggled Method of using PP OPT to give SE outpur was pentode amplifiers
On Nov 6, 12:42 am, John Byrns wrote:
In article . com, Multi-grid wrote: On Nov 4, 4:43 pm, Andre Jute wrote: They're your words and they don't make sense to me. Take all the space you need. Please feel free to treat me as a total ignoramus and explain in words of one syllable, with all the tees crossed and all the eyes dotted so that there can be no misunderstanding. A schematic is always good to avoid misunderstanding. What don't you 'get'? Think some more. Think 'ampere-turns'. Take a primary of two to three thousand turns, and run 100 mA through it. Put this coil around a minimum gap/alternate stacked E-I or cut C-core. What happens to the flux? Got an answer yet? Take another winding, and run the filament current through it. It is substantially larger than 0.1 Ampere( actually 25 A was my example). You should energize the correct end of this winding, eh? Andre, notice how Multi-grid is avoiding your question, and being evasive about how this scheme actually works. It is straight forward to use the filament current to provide the bias to the core to offset the current from the amplifier tube, or any other current for that matter, as long as the number of ampere-turns is the same as in the active primary, as Multi-grid points out. Unfortunately the issue that Multi-grid doesn't want to deal with, or can't, is that a substantial portion of the audio power generated by the active tube is dissipated across the filament resistance of the tube and never makes it to the speaker. The bottom line is that this circuit doesn't work very well when built as Multi-grid describes it. The problem can be dealt with, but dealing with it adds considerable extra cost, which makes one wonder why anyone in their right mind would take this approach to building an amplifier in the first place? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/- Hide quoted text - - Show quoted text - Well John I've made it plain that I am not going to hand this out. It isn't any fun for you, and it is too much work for me. So get with it if you can. Just remember, I know your belief or understading isn't required, I've seen it in action. You have yet to do anything which deserves my indulgence of your lazy and closed mind. Behave yourself. cheers, Douglas I'll give you a hint: Think about the power, you've come to an incorrect conclusion. See if you can find it. |
#79
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The Duggled Method of using PP OPT to give SE outpur was pentode amplifiers
On Nov 5, 10:42 pm, John Byrns wrote:
In article . com, Multi-grid wrote: On Nov 4, 4:43 pm, Andre Jute wrote: They're your words and they don't make sense to me. Take all the space you need. Please feel free to treat me as a total ignoramus and explain in words of one syllable, with all the tees crossed and all the eyes dotted so that there can be no misunderstanding. A schematic is always good to avoid misunderstanding. What don't you 'get'? Think some more. Think 'ampere-turns'. Take a primary of two to three thousand turns, and run 100 mA through it. Put this coil around a minimum gap/alternate stacked E-I or cut C-core. What happens to the flux? Got an answer yet? Take another winding, and run the filament current through it. It is substantially larger than 0.1 Ampere( actually 25 A was my example). You should energize the correct end of this winding, eh? Andre, notice how Multi-grid is avoiding your question, and being evasive about how this scheme actually works. It is straight forward to use the filament current to provide the bias to the core to offset the current from the amplifier tube, or any other current for that matter, as long as the number of ampere-turns is the same as in the active primary, as Multi-grid points out. Yes, but that means a specially wound transformer, a vast expense in the context of trying to use a junkbox or at least existing PP transformer for SE. Plus a cap and probably a choke that Multi-Cuddles doesn't mention, and soon you're into real money. This isn't an innovation, this is a kludge to bodge right another kludge. Unfortunately the issue that Multi-grid doesn't want to deal with, or can't, is that a substantial portion of the audio power generated by the active tube is dissipated across the filament resistance of the tube and never makes it to the speaker. Yah. This is why I wrote to Robert Casey that I have zero faith in these heathrobinson schemes because I have never managed to run more than a tiny fraction of the PP current through a PP trx being used for SE, not if I wanted a result that satisfied my noise criteria anyway. It's a novelty, not a circuit. The bottom line is that this circuit doesn't work very well when built as Multi-grid describes it. The problem can be dealt with, but dealing with it adds considerable extra cost, which makes one wonder why anyone in their right mind would take this approach to building an amplifier in the first place? At the time that Bottlehead took his Electronic Tonalities all- parafeed, he said it was because it sounded better. I believe him, that it sounds better to him and his circle of very competent DIYers. But I like conservative engineering, especially KISS. I'd rather spend the same money that goes into parafeed on a proper SE output and just put the bloody current through the primary. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ Oh well, there goes another perpetual motion machine into the free- lunch chute to infinity. 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 |
#80
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pentode amplifiers
On Nov 5, 7:37 pm, "Dave" wrote:
"Andre Jute" wrote in message ups.com... ). Sure. I don't know how you will build it. I have to assume you know enough to ground your chassis! I also assume you will use a three- point (IEC) grounded plug, not those dangerous American two-point things. Isn't there a rationale floating around out there that says that if you mains ground every piece of audio gear, you'll end up with ground loops? Don't overcomplicate matters when you're starting out. You're not building "every piece of audio gear". You're building a power amp that will have exposed metal and high voltages. You shouldn't leave it floating. Therefore you must ground it. If you ground it as I suggest, and if your wiring is tidy (short, cross at right angles, well enough separated -- air is the best dielectric), then you will be surprised at how little rubbish you pick up either out of the air or on the mains wire. The ground circuit that I suggest, if laid out like the one I gave a URL for, will have all 0V lines connected to a star at the bottom of the bleeder, a short line from there to the mains ground at the 3-point plug, and a short line from the mains ground to a chassis connection right next to the plug. There is very little to loop here. It would in fact be very difficult for a potential difference to arise in the ground wiring in such a scheme. That is why I suggest it; it is part of the silence of the amp! Wouldn't tying your signal ground to mains earth potentially amplify any noise on the ground circuit, i.e. hum from your fridge motor and everything else? Forget it until it happens, then you can fix it. I used to put a mains rated cap across the mains but no longer do it and don't show it on new circuits because I know of nobody who found it necessary (and it is dangerous to get that cap wrong). If and when it happens, you buy a filter. Andre Jute "Garbage in, garbage out." -- Programmer's warning. "Wiki in, wiki out." -- Al Marcy. |
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