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Variable capacitors, etc. (was AM Tuner...)
This thread is very timely in that I, too, am interesting in building
a high-performance, aesthetically-pleasing tube-based AM tuner. One which has very good output audio quality (when feeding a separate amplifier), which will be an excellent MW DX machine, and which is aesthetically pleasing, reminiscent of the radio chassis' of the 1930's (for example, usable in modern renditions of the classic radio style -- a separate tube amp component would be added as needed.) Craig's list eerily matches mine almost exactly, so there are at least two of us in the world wanting and willing to go to all this trouble. Anyone else here interested in the same? I've thought of creating a Yahoo Group devoted to discussing and encouraging the design of such a hybrid (tube/solid state) component. Would anyone even bother to join such a group and contribute? smile/ On a semi-related topic, I am perplexed in that some say, for a newly designed chassis, that I will not be able to find new (modern) tuning capacitors akin to the ones of old -- that I'd have to settle for varactor tuning. I look on the Internet and I find at least two manufacturers who make just such tuning capacitors. They probably are fairly expensive, even when bought in larger lots, but nevertheless they *are* available. It would not surprise me that one could even buy a modern tuning capacitor to workably replace a damaged one in certain models of older radios. I see new multiple-gang 365pF tuning caps, for example -- all over the place, actually. The two companies I found so far which manufacture air variables include: Oren Elliott: http://www.orenelliottproducts.com/ Jackson Brothers: http://www.mainlinegroup.co.uk/jacksonbrothers/ Any other tuning capacitor manufacturers I missed? (And out of curiousity, are there alternate designs for airgap tuning capacitors besides the "meshing fin" type? I've been intrigued, mostly for the fun of it, with a sliding tube-in-tube design -- the damn thing should work as I think about it, should not be too big, and because it is linear in movement (rather than rotational), will better mechanically match a slide-rule dial.) Comments on this? I'm also curious to know if a varactor system can be designed which would deliver the same level of performance as a higher-quality tuning capacitor? I get the impression from my web research that even the high-quality varactors are more prone to drift, are thermally more sensitive, have higher noise levels, lower Q values, and other anomalies that make them less desirable than comparable tuning caps. On the other hand, I was told that properly designed and selected varactors could reduce or eliminate the need for alignment. Comments on this? Thanks. Jon |
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#2
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Jon Noring wrote:
This thread is very timely in that I, too, am interesting in building a high-performance, aesthetically-pleasing tube-based AM tuner. Anyone else here interested in the same? I've thought of creating a Yahoo Group devoted to discussing and encouraging the design of such a hybrid (tube/solid state) component. Would anyone even bother to join such a group and contribute? smile/ On a semi-related topic, I am perplexed in that some say, for a newly designed chassis, that I will not be able to find new (modern) tuning capacitors akin to the ones of old -- that I'd have to settle for varactor tuning. I look on the Internet and I find at least two manufacturers who make just such tuning capacitors. They probably are fairly expensive, even when bought in larger lots, but nevertheless they *are* available. It would not surprise me that one could even buy a modern tuning capacitor to workably replace a damaged one in certain models of older radios. I see new multiple-gang 365pF tuning caps, for example -- all over the place, actually. On the other hand, I was told that properly designed and selected varactors could reduce or eliminate the need for alignment. Comments on this? Thanks. Jon I appreciate anyone who wants to build their own gear just for the fun of it. Homebrew amps, for instance, are very popular because they are fairly simple to build. I think you zeroed in on one of the minor problems just looking for the variable cap you want...the best source is a $10 (complete) piece of ebay gear that does everything you want already with a bit of restoration. You can buy some old Lafayette tuner for such prices and they come with all the parts, pre-drilled chassis, front panel facia, dial stringing mechanisms, etc. and will no doubt be better than some cobbled together thing. Someone else already mentioned "re-inventing the wheel". The subject often comes up with us old-radio folk about "kits" of even the simplest radio like what used to be offered in the 50s-60s. You still run across them on ebay at big bux but I have yet to see why just tearing down and old rig and rebuilding it into your own chassis/cigar box isn't a suitable substitute for the homebrew 'anxt'? Homebrewing, by its nature, tends to be a hobby in itself. It means that a complex project never quite gets finished or never quite reaches the intended goal of having a 100% functional piece of gear because there's always a new tweak to try. Nothing wrong with that, the fun of homebrewing is lacing with other like minds and trying different stuff and learning a lot. If you want a good AM tuner, go to ebay. If you want to homebrew start by checking price/availablity of the components and see if thats really what you want to get into. Good luck, whichever way you decide. -Bill |
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#3
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#4
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Hey, why do all this work when you can get a killer EH Scott 800B chassis,
nice chrome and all, with power supply/audio chassis for a reasonable amount like $250??? I mean, the mono block amp on that is like a Mac 60! Weighs a ton too, you should see the massive xfmr... PP 6L6 I think... Now, you rig the low level output to it, and there you go.... you get FM and SW to boot! AND its all chrome to look cool. I have one for sale at this price, mine is grimy and needs a look over./ recap....email me if interested... do a google search for EH Scott for info on these... somebody would have a page with one I bet. I have all the schematics and stuff... there is tons in Rider 15 I think on it. Sensitivity control, bandwidth, IIRC. I have a RARE version of the Scott Phantom, fully restored, recapped, etc, with speaker, $800. No cabinet . Mark Oppat "Jon Noring" wrote in message om... This thread is very timely in that I, too, am interesting in building a high-performance, aesthetically-pleasing tube-based AM tuner. One which has very good output audio quality (when feeding a separate amplifier), which will be an excellent MW DX machine, and which is aesthetically pleasing, reminiscent of the radio chassis' of the 1930's (for example, usable in modern renditions of the classic radio style -- a separate tube amp component would be added as needed.) Craig's list eerily matches mine almost exactly, so there are at least two of us in the world wanting and willing to go to all this trouble. Anyone else here interested in the same? I've thought of creating a Yahoo Group devoted to discussing and encouraging the design of such a hybrid (tube/solid state) component. Would anyone even bother to join such a group and contribute? smile/ On a semi-related topic, I am perplexed in that some say, for a newly designed chassis, that I will not be able to find new (modern) tuning capacitors akin to the ones of old -- that I'd have to settle for varactor tuning. I look on the Internet and I find at least two manufacturers who make just such tuning capacitors. They probably are fairly expensive, even when bought in larger lots, but nevertheless they *are* available. It would not surprise me that one could even buy a modern tuning capacitor to workably replace a damaged one in certain models of older radios. I see new multiple-gang 365pF tuning caps, for example -- all over the place, actually. The two companies I found so far which manufacture air variables include: Oren Elliott: http://www.orenelliottproducts.com/ Jackson Brothers: http://www.mainlinegroup.co.uk/jacksonbrothers/ Any other tuning capacitor manufacturers I missed? (And out of curiousity, are there alternate designs for airgap tuning capacitors besides the "meshing fin" type? I've been intrigued, mostly for the fun of it, with a sliding tube-in-tube design -- the damn thing should work as I think about it, should not be too big, and because it is linear in movement (rather than rotational), will better mechanically match a slide-rule dial.) Comments on this? I'm also curious to know if a varactor system can be designed which would deliver the same level of performance as a higher-quality tuning capacitor? I get the impression from my web research that even the high-quality varactors are more prone to drift, are thermally more sensitive, have higher noise levels, lower Q values, and other anomalies that make them less desirable than comparable tuning caps. On the other hand, I was told that properly designed and selected varactors could reduce or eliminate the need for alignment. Comments on this? Thanks. Jon |
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#5
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Behold, Jon Noring scribbled:
Craig's list eerily matches mine almost exactly, so there are at least two of us in the world wanting and willing to go to all this trouble. Anyone else here interested in the same? I've thought of creating a Yahoo Group devoted to discussing and encouraging the design of such a hybrid (tube/solid state) component. Would anyone even bother to join such a group and contribute? smile/ I am building a LW/MW/SW receiver myself. I have a keister kickin' preselector and balanced 6J6 mixer designed and am now working on decent I.F. stages using 6CB6's. I have a forum for such topics if you are interested: http://geek.scorpiorising.ca/cgi-bin/yabb/YaBB.pl Listen not to naysayers - this "true" homebrew is the heartbeat of mad scientists worldwide and a field that was previously held only by the radio amateur's. Hmmm, funny - now *they* are all buying the store stuff and *we* are the exprimentors :-p -- Gregg *It's probably useful, even if it can't be SPICE'd* |
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#6
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Jon Noring wrote: This thread is very timely in that I, too, am interesting in building a high-performance, aesthetically-pleasing tube-based AM tuner. One which has very good output audio quality (when feeding a separate amplifier), which will be an excellent MW DX machine, and which is aesthetically pleasing, reminiscent of the radio chassis' of the 1930's (for example, usable in modern renditions of the classic radio style -- a separate tube amp component would be added as needed.) Just some thoughts... Nothing at all wrong with building it yourself, in my book. I've built a radio from sheet metal up (my senior high school electronics project) - and while it was nothing remarkable in it's design (basic AA5 plus eye tuning tube) the pride in the accomplishment of building it from truly scratch is hard to match. Note though - even with all the work - it performed as it was - an AA5 - a lot of work for what (functionally) could be had off the shelf (then) for around $5.00. As has been noted here by others - there is little on the AM band any more worth "serious" listening. Some - indeed - but worth the proposed effort? Hmmmm.... There are some seriously good performers out there that are ready made, and with some fairly minor modifications - could be excellent performers meeting all of your "specifications". From a pure "performance wise" perspective - there are radios out there-- that there is no way you could ever match their performance with a hand made set, period. Of course - most of those don't meet some of your "specifications" - as they tend to be a bit - uh - well let's just say esthetics wasn't in the original specs. But for raw "excellent DX machine" characteristics - there are receivers that are in a class by themselves. Point being - you're not going to build something that's going to "outclass" all prior sets / technologies--- you're going to have to settle on some compromises - as have most manufacturers over the years. And that sets the challenge: Just listing some general specifications is nice - but meaningless. What you have to decide is what are your true goals? Design Specifics: What is to be the s+n/n for 20db recovered audio? What is the selectivity? How is AGC to be generated and processed? Selectable time constants? What is the passband? Is Passband to be managed in the IF? RF? If passband is to be variable- how is that to be managed? Serious DX implies more tools: Limiting- Fixed? Variable? Audio filters? Again - fixed? variable? shelf or notch? What about detection? just simple diode? or get really serious with something like synchronous detection? This is my point - "building" an "above average" receiver can get crazy- and I'm wondering (as others may have sort of mentioned) if it wouldn't make more sense to start with a pretty good design receiver already working - and perhaps "hot rod" it up. Not try rebuild it "chassis up" - but just tweak where economics dictated some original compromises that can be "souped up". Starting with a "decent" AM tuner - areas begging for tweaks: the IF - stagger tuning a decent IF can make a good sounding radio rock- though obviously you sacrifice selectivity. How about adding a (switchable) 2nd IF chain - one tight and highly peaked - the other broad - and sounding good? AGC - allowing switchable - or variable time constants can make a good "listening" radio better for DX - and vice versa. And that's a fairly minor mod- yet one that can make remarkable differences in how the radio "responds". If you try and do all of this "from scratch" how long will it take just to get the radio "right" in the first place - just to get it to where you can start "playing" with the variables? On a semi-related topic, I am perplexed in that some say, for a newly designed chassis, that I will not be able to find new (modern) tuning capacitors akin to the ones of old -- Naw - standard variables are very easy to come by - and far easier to design with- particularly when it comes to tight tracking. Most varactor front-ends are like open barn doors... (yech!). (And out of curiousity, are there alternate designs for airgap tuning capacitors besides the "meshing fin" type? I've been intrigued, mostly for the fun of it, with a sliding tube-in-tube design -- the damn thing should work as I think about it, should not be too big, and because it is linear in movement (rather than rotational), will better mechanically match a slide-rule dial.) Crosley used "book" type capacitors for a while (invented by Gernsback - who supposedly (according to some here) never invented anything)... They work, are simple to home-brew, etc. Obviously - most manufacturers feel "mesh" type caps (with non-linear plates) were better - for various reasons. I have a hunch the "tube-in-tube" design you're thinking about aren't really variable tuning caps at all - but rather variable inductor tuning systems - used in most tube car radios - and high-end tube receivers and transmitters. Collins highest end designed gear is famous for it's "permeability tuning"... being extraordinarily stable - and unfortunately - equally complex. This comes back to what I was saying earlier about being near impossible to hand duplicate some of the top high-end designs - just take a look at an R-39X/x geartrain - and you'll see what I mean. But many people believe that is the best general purpose (AM/SW) receiver ever designed. Back to the tube-in-tube - there are both ceramic and glass versions of these - that are variable - or rather - semi-fixed. they usually are used as trimmers rather than main tuning - as their range is usually pretty small. I'm also curious to know if a varactor system can be designed which would deliver the same level of performance as a higher-quality tuning capacitor? Obviously - with very complex tracking PLL control designs now boiled down to a chip - varactors can be tamed-- but you're talking about circuit complexities that are orders of magnitude beyond what "usual" experimenters are capable of - or have the equipment to work with. And I've yet to see any radio - at any price "blow off" a properly aligned, etc. R390A. Neither has anyone else. But we're talking apples and oranges here... I've seen some car receivers that are nothing short of impressive on AM... with rock stable L.O.s, and the attendant precision that goes with it- they make DXing an almost ho-hum activity. Again - you need to decide - in well "nailed down" terms - just what specifications you want your "receiver" to meet. Then decide how best to meet those specs. If you just zing off to build something - "something" (other than your ideal receiver) is what you'll end up with... as you noted - just some thoughts... -- randy guttery A Tender Tale - a page dedicated to those Ships and Crews so vital to the United States Silent Service: http://tendertale.com |
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#7
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Jon Noring wrote: This thread is very timely in that I, too, am interesting in building a high-performance, aesthetically-pleasing tube-based AM tuner. One which has very good output audio quality (when feeding a separate amplifier), which will be an excellent MW DX machine, and which is aesthetically pleasing, reminiscent of the radio chassis' of the 1930's (for example, usable in modern renditions of the classic radio style -- a separate tube amp component would be added as needed.) But what you are upagainst with AM DXing is an atmosphere determined to spoil your expectations, since what comes from an antenna is so bleedin noisy. I live in Canberra, 200 miles from powerful Sydney stations, and no matter how good my reciever is, its just lousy listening if I try to listen in to Sydney stations, because there are so many others at high enough strengths to cause unbearable interference. Then there is the crackles and buzzes of randon noises. Its possible to have several antennas, going in different directions and play games with phase and nulling out stations which are interfering. The radio set can't do this on it's own. In Oz, all AM stations are spaced 9 kHz apart, and there are stations in different parts of the nation which have the same frequency. if you live midway between either station, you pick up both at simialr strength, and unless you have a special antenna which is directional, you won't seperate the signals, and even so, the seperation won't be complete. Craig's list eerily matches mine almost exactly, so there are at least two of us in the world wanting and willing to go to all this trouble. Anyone else here interested in the same? I've thought of creating a Yahoo Group devoted to discussing and encouraging the design of such a hybrid (tube/solid state) component. Would anyone even bother to join such a group and contribute? smile/ I'm all for building a decent AM radio. I couldn't find any that were magic, even for local reception, except a Quad AM tuner, which isn't bad. But I reckoned I could improove on Quad, so I just did, which meant spending time at the local uni, in the library basement, going through a lot of old smelly books to learn about old radio theory. Then I went home with a lot of photo copied stuff, and started building something. This is the way, and don't let anyone stop you. But there is little interest in good DX, because ppl in the know see its pointless to try for good hi-fi standard DX listening. In 1935 the airwaves were fairly clean, but now they are filthy. On a semi-related topic, I am perplexed in that some say, for a newly designed chassis, that I will not be able to find new (modern) tuning capacitors akin to the ones of old -- that I'd have to settle for varactor tuning. I look on the Internet and I find at least two manufacturers who make just such tuning capacitors. They probably are fairly expensive, even when bought in larger lots, but nevertheless they *are* available. It would not surprise me that one could even buy a modern tuning capacitor to workably replace a damaged one in certain models of older radios. I see new multiple-gang 365pF tuning caps, for example -- all over the place, actually. The two companies I found so far which manufacture air variables include: Oren Elliott: http://www.orenelliottproducts.com/ Jackson Brothers: http://www.mainlinegroup.co.uk/jacksonbrothers/ Any other tuning capacitor manufacturers I missed? But I have about at least 20 tuning caps, dual, triple, 20 pF to about 500pF, and from these one day I might build something again. I never paid much for them, and if you knew who to get to know, you should be able to pick up some good old gear easily. But if you don't mind spending the money, buy new gear. And most old radios did not have variable inductors, which can be used in addition to variable caps, and the firms above make these to. (And out of curiousity, are there alternate designs for airgap tuning capacitors besides the "meshing fin" type? I've been intrigued, mostly for the fun of it, with a sliding tube-in-tube design -- the damn thing should work as I think about it, should not be too big, and because it is linear in movement (rather than rotational), will better mechanically match a slide-rule dial.) The slide type of concentric tubes has been used for trimmer caps, often screw adjusted, say 3 to 43 pF. The air gang meshing vari-cap has a logarithmic increase/decrease in capacitance for the degrees of turn, or else you'd have most of the stations at one end of the dial. Its far easier to make the existing flat plate intermeshing caps, than it is to make the same using curved plates, ie, tubes. Comments on this? I'm also curious to know if a varactor system can be designed which would deliver the same level of performance as a higher-quality tuning capacitor? Modern AM radio sets use a DC voltage to tune the vearactor caps right across the band. The metal tuning cap became obsolete the day after the veractor became viable. An the veractor allowed fine tuning, and PLL control of frequency. Most of these SS AM radios sound like crap. Probably the combination of lots of things causes this. I get the impression from my web research that even the high-quality varactors are more prone to drift, are thermally more sensitive, have higher noise levels, lower Q values, and other anomalies that make them less desirable than comparable tuning caps. On the other hand, I was told that properly designed and selected varactors could reduce or eliminate the need for alignment. Comments on this? It depends. Say you had an oscillator which created EXACTLY the same reliable F at the press of a button. No drift, and the station wanted is right there. No tuning, because the stations are all set apart exactly 9 kHz, like all the recievers' oscillator settings. There is no need to use a tuning gang if PLL and other AFC techniques are used to do it all, but to do all this with tubes would take a house full of tubes. With a few chips, its easy. I'd always prefer a steam powered radio, ie, one with tubes, coils, and a tuning gang. I just don't like modernity, when it comes to radios. If one is in doubt about whether or not you are right on a station, fit a tuning eye, or an S meter, simple. Patrick Turner. Thanks. Jon |
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#8
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Gregg wrote: Behold, Jon Noring scribbled: Craig's list eerily matches mine almost exactly, so there are at least two of us in the world wanting and willing to go to all this trouble. Anyone else here interested in the same? I've thought of creating a Yahoo Group devoted to discussing and encouraging the design of such a hybrid (tube/solid state) component. Would anyone even bother to join such a group and contribute? smile/ I am building a LW/MW/SW receiver myself. I have a keister kickin' preselector and balanced 6J6 mixer designed and am now working on decent I.F. stages using 6CB6's. I have a forum for such topics if you are interested: http://geek.scorpiorising.ca/cgi-bin/yabb/YaBB.pl I just tried to log in, but it kept giving me an error message Listen not to naysayers - this "true" homebrew is the heartbeat of mad scientists worldwide and a field that was previously held only by the radio amateur's. Hmmm, funny - now *they* are all buying the store stuff and *we* are the exprimentors :-p But fascination and wonderment is its own reward. -- Gregg *It's probably useful, even if it can't be SPICE'd* Patrick Turner. |
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#9
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Randy and/or Sherry wrote: Look - I'm not suggesting that an R390/A etc. is appropriate for your project - but I do get a little bemused that so many people "think" that just because it's geewhizbang modern it'll trash the old equipment... A case in point. I just finished doing some touch up alignment on my 1949 GE 10T1 B/W television. There are two gewhizband modern television sets in the house and with rabbit ears, neither one will pull in the NBC affiliate station which is about 50 miles away. This old GE will pull it in (although with a goodly amount of snow) with rabbit ears sitting in the basement. Bill H. |
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#10
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Gregg wrote: Listen not to naysayers - this "true" homebrew is the heartbeat of mad scientists worldwide and a field that was previously held only by the radio amateur's. Hmmm, funny - now *they* are all buying the store stuff and *we* are the exprimentors :-p Do you have any idea how many 12AX7s it takes to do spread spectrum code generation and or digital signal processing? Jeff -- "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." Benjamin Franklin "A life lived in fear is a life half lived." Tara Morice as Fran, from the movie "Strictly Ballroom" |
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#11
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Mark Oppat wrote:
Hey, why do all this work when you can get a killer EH Scott 800B chassis, nice chrome and all, with power supply/audio chassis for a reasonable amount like $250??? Many have called attention to the fact that tube-based AM radio circuit design probably hit its "zenith" (pun not intended) back in the late 1930's through the 1950's. Since my interest is in building a tube-based AM tuner using modern components, adapting the circuit design of a highly reputed older radio is certainly intriguing. Just remove the final audio amplifier section (and tweak the line-out as necessary to conform it with today's standards), and maybe replace a few other "autonomous" sections with modern solid-state equivalents if there is any advantage to do so (e.g., the DC power supplies.) Of course, it continues to be suggested to just find an older radio and cannibalize it to my heart's content. In my case, by the time I've cannibalized it and rebuilt the chassis, the mechanicals, replaced all wiring, resistors, caps, etc., etc., it probably would have been better to just build the damn thing from scratch per a schematic and general layout. Thus the idea is to come up with a general schematic and layout design, and build from that. And once a group of enthusiasts have come up with a working design with schematics (a Mark "I" model), then lots of people who like to build their own "homebrew" audio components can then just build to the schematic, order the parts, follow some guidelines, and away they go. No need to scrounge around looking for 60 year old tuning capacitors from model such-and-such, or to use odd-ball tubes which are difficult to find. The design would, by-and-large, use new, "off-the-shelf" parts. Maybe only one or two parts will require custom building, but then they could be specially built in lots of 100 or so if the enthusiasts band together to make this happen. Also, the point brought up by Randy Guttery is valid: it is difficult to design an AM tuner which perfectly and simultaneously meets all requirements under the sun. There are always compromises to be made. It may be possible to design the tuner to have the performance of a Collins R-390A (which Randy mentioned) but then the complexity of the circuitry and mechanicals elevates it up to the stratosphere -- only large companies could afford the tool-up costs to build the thing, or the enthusiast would need access to a machine shop, and lots and lots of $$$$$, to custom build the various mechanicals and certain electronic parts for it (a *major* undertaking even for the very experienced, and not a two-weekend project for the average tube audio "homebrewer".) The key is to be reasonable. I think the key is to shoot for the 80-90% level on all requirements: 1) that 80-90% of *all* MW DXers would find its performance to be quite acceptable and they would consider using it for their DXpeditions (using their own antenna systems of course -- the antenna is the key to performance anyway -- lots of MW DXers use quite "simple" radios but with good antennas get acceptable DX results), 2) that 80-90% of all tube audio enthusiasts would find its line-out audio quality to be acceptable for listening pleasure (given a strong local station of good broadcast audio quality -- most tube audio enthusiasts will *know* not to expect CD-audio quality, but they'd like low distortion and low noise -- a good and pleasing sound from what they expect from "AM"), 3) that 80-90% of those who love the aesthetics of the old tube radios will enjoy this design, and a few may actually wish to build it and place it into a 1930's-inspired cabinet for it (or if they have an old cabinet sans chassis, to use this in place of the original chassis), and 4) that 80-90% of those who routinely build "homebrew" tube audio equipment would be able to build this AM tuner design from scratch or from a "kit". (This does suggest a fairly simple and stable circuit, not requiring much in the way of adjustment or tweaking, and no elaborate mechanicals -- for example, a single multi-gang tuning cap would be all the mechanicals they need to worry about.) (The next step would be to translate the above general requirements into a list of more specific requirements, such as Randy recommended in his message.) So, rather than re-inventing the wheel, based on the general requirements given above, what tube radio/tuner of yesteryear (from the 1930's to 1960's) would make a good candidate as the starting-point for the design of this new "Mark I Tube AM Tuner"? I look forward to the list of candidates. :^) Jon |
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#12
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Behold, Patrick Turner scribbled:
I have a forum for such topics if you are interested: http://geek.scorpiorising.ca/cgi-bin/yabb/YaBB.pl I just tried to log in, but it kept giving me an error message What kinda error? -- Gregg *It's probably useful, even if it can't be SPICE'd* |
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#13
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Behold, Jeffrey D Angus scribbled:
Gregg wrote: Listen not to naysayers - this "true" homebrew is the heartbeat of mad scientists worldwide and a field that was previously held only by the radio amateur's. Hmmm, funny - now *they* are all buying the store stuff and *we* are the exprimentors :-p Do you have any idea how many 12AX7s it takes to do spread spectrum code generation and or digital signal processing? Jeff I dunno, I used 12AU7's ;-) -- Gregg *It's probably useful, even if it can't be SPICE'd* |
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#14
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Jon Noring wrote: So, rather than re-inventing the wheel, based on the general requirements given above, what tube radio/tuner of yesteryear (from the 1930's to 1960's) would make a good candidate as the starting-point for the design of this new "Mark I Tube AM Tuner"? I'll recommend at least one circuit to look at - Radio Craft ran a series on a 30 tube "Super-Deluxe" radio - four chassis - tuner, IF, AF and power - Seems like it had just about every "bell and whistle" an AM receiver could have - for technology of the time- which as noted - was getting pretty mature. I'm sure there are ideas that have come along since that might make better sense now - but for a basic blueprint of a build-it-yourself radio (including practical / reachable goals) - that should be at the very least something to study. I don't have those issues -- only the reprint of the March 1938 "50 Years of Radio" edition... which contained part 6 - the last part of the construction series. So perhaps someone that does have there could pull them - particularly the RF / IF sections - and see what's there (scan post schematic / specs?????)... -- randy guttery A Tender Tale - a page dedicated to those Ships and Crews so vital to the United States Silent Service: http://tendertale.com |
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#16
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donut wrote:
Here's an idea. Fair Radio Sales is offering a Concord permeability tuning assembly for an AA5 lineup. NOS, $14.95. It looks to be a complete assembly with a fairly large wheel for tuner cord. Yes, it would lack the RF section. The way around that is a ferrite loop tuned by a separate cap. Even a small transistor type tuning cap would suffice for that. The loop could be mounted inside the cabinet and rotated by a front panel knob. An old tube AM car radio will likely have a permeability tuning assembly with an RF stage. Remove or modify the radio for your project. |
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#17
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Jon Noring wrote: Not that it would be used in lieu of modern equipment, Don't sell the tubes short - there are precious few - if any SS receivers that'll beat a top performing R390A... Add a Sherwood synchronous product detector - and WOW! See... http://www.r390a.com/html/history.htm Look - I'm not suggesting that an R390/A etc. is appropriate for your project - but I do get a little bemused that so many people "think" that just because it's geewhizbang modern it'll trash the old equipment... As noted - receiver design peaked at the end of the "golden era" - and that ended in the 50's. Digital tuning, etc. are nice - and certainly have their place - but they also often come with excess baggage (like phase noise / jitter / etc.) that are undesirable. And when you start getting down into the .07 .08 uv 10 db s+n/n region - noise floor is a concern. Fidelity was never a strong point in the 390s - the Sherwood Synchronous product detector makes a major improvement on that for DXing, - the 390's naked 16Khz passband is good enough for me for local "stuff". just my .02 -- randy guttery A Tender Tale - a page dedicated to those Ships and Crews so vital to the United States Silent Service: http://tendertale.com |
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#18
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Gregg wrote: Behold, Patrick Turner scribbled: I have a forum for such topics if you are interested: http://geek.scorpiorising.ca/cgi-bin/yabb/YaBB.pl I just tried to log in, but it kept giving me an error message What kinda error? It just kept teeling me I didn't have the right username, so I tried a few variations, and gave up. Patrick Turner. -- Gregg *It's probably useful, even if it can't be SPICE'd* |
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#19
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then register yourself as "olde grumpy one" and use "iiiiiiihhhhhhaaaaaaa"
as password  )-- Choky Prodanovic Aleksandar YU "Patrick Turner" wrote in message ... It just kept teeling me I didn't have the right username, so I tried a few variations, and gave up. Patrick Turner. -- Gregg *It's probably useful, even if it can't be SPICE'd* |
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#20
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BH wrote:
Randy and/or Sherry wrote: Look - I'm not suggesting that an R390/A etc. is appropriate for your project - but I do get a little bemused that so many people "think" that just because it's geewhizbang modern it'll trash the old equipment... A case in point. I just finished doing some touch up alignment on my 1949 GE 10T1 B/W television. There are two gewhizband modern television sets in the house and with rabbit ears, neither one will pull in the NBC affiliate station which is about 50 miles away. This old GE will pull it in (although with a goodly amount of snow) with rabbit ears sitting in the basement. Bill H. The modern sets are designed for use on cable TV, unlike the tube set was designed when stations were less common, and harder to receive. More IF stages give more system gain, and allow you to pull a snow signal in on the tube tv set. -- Michael A. Terrell Central Florida |
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#21
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Jeffrey D Angus wrote:
Do you have any idea how many 12AX7s it takes to do spread spectrum code generation and or digital signal processing? Jeff Not to mention all those 20 ton air conditioners. -- Michael A. Terrell Central Florida |
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#22
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Michael A. Terrell wrote:
BH wrote: Randy and/or Sherry wrote: A case in point. I just finished doing some touch up alignment on my 1949 GE 10T1 B/W television. There are two gewhizband modern television sets in the house and with rabbit ears, neither one will pull in the NBC affiliate station which is about 50 miles away. This old GE will pull it in (although with a goodly amount of snow) with rabbit ears sitting in the basement. Bill H. The modern sets are designed for use on cable TV, unlike the tube set was designed when stations were less common, and harder to receive. More IF stages give more system gain, and allow you to pull a snow signal in on the tube tv set. As a cable guy I participated in a field test with a handful of manufacturers in 1974-ish. Basically they were just entering the era of adjacent channel tuners and overall sensitivity. Even in 1974 the cheapest K-Mart model would have run rings around any 'tube' set. There's unequivocably no reduction in reception capability in a "modern" set because of "being designed for cable tv". If anything the opposite is true. Front ends in tube sets had a noise figure on the order of 6-8 db in the best cases, nowadays a $19 K-Mart camping set will easily comply at less than 2db, and a better 'home' set approaches 1db. IF gain has nothing to do with "pulling a snow signal" and Michael A, you should know that. All that being said, for a tinkerer yanking a signal out of the air and actually having it look good on an old b/w toober is worth about 40 db of congratulatory signal increase....20db because its b/w and another 20db as a "celebration" that the old dinosaur actually works. -Bill |
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#23
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Michael A. Terrell wrote:
Jeffrey D Angus wrote: Do you have any idea how many 12AX7s it takes to do spread spectrum code generation and or digital signal processing? Jeff Not to mention all those 20 ton air conditioners. Uh-huh. -BM |
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#24
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54-46 was my number wrote:
Michael A. Terrell wrote: BH wrote: Randy and/or Sherry wrote: A case in point. I just finished doing some touch up alignment on my 1949 GE 10T1 B/W television. There are two gewhizband modern television sets in the house and with rabbit ears, neither one will pull in the NBC affiliate station which is about 50 miles away. This old GE will pull it in (although with a goodly amount of snow) with rabbit ears sitting in the basement. Bill H. The modern sets are designed for use on cable TV, unlike the tube set was designed when stations were less common, and harder to receive. More IF stages give more system gain, and allow you to pull a snow signal in on the tube tv set. As a cable guy I participated in a field test with a handful of manufacturers in 1974-ish. Basically they were just entering the era of adjacent channel tuners and overall sensitivity. Even in 1974 the cheapest K-Mart model would have run rings around any 'tube' set. There's unequivocably no reduction in reception capability in a "modern" set because of "being designed for cable tv". If anything the opposite is true. Front ends in tube sets had a noise figure on the order of 6-8 db in the best cases, nowadays a $19 K-Mart camping set will easily comply at less than 2db, and a better 'home' set approaches 1db. IF gain has nothing to do with "pulling a snow signal" and Michael A, you should know that. All that being said, for a tinkerer yanking a signal out of the air and actually having it look good on an old b/w toober is worth about 40 db of congratulatory signal increase....20db because its b/w and another 20db as a "celebration" that the old dinosaur actually works. -Bill I worked on several 12 channel Vicoa/ Coral/ Vicor systems in 1972 & 1973 at Ft Rucker alabama, and we had a separate, 12 channel system as a return loop because no one sold bi-directional equipment when it was built. It was one of the early 30 volt trunk powered systems, so you needed lots of pole mounted power supplies. The amplifier modules were built before the TRW or Motorola hybrid amps, so everything was point to point wired. Some of the older TV sets had a wider AGC range, and would handle weaker signals better. Some new sets drop out around -15 dB, and I have seen a snowy picture on some old sets that I couldn't read a level with a Sadelco FSM. Not all of them had extra gain, but some were surprisingly sensitive. -- Michael A. Terrell Central Florida |
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#25
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"Michael A. Terrell" writes:
Jeffrey D Angus wrote: Do you have any idea how many 12AX7s it takes to do spread spectrum code generation and or digital signal processing? Jeff Not to mention all those 20 ton air conditioners. It is all about time. You can build all the computation blocks with memory (delay line) and only a few gates; i.e., a few tubes. You make the tradeoffs word-length/speed/tubes. Motorola once made a 1-bit microprocessor that worked this way (serial computation). This was the MC14500. One could build something like this with a minimum number of tubes. -- Michael A. Terrell Central Florida -- Steven D. Swift, , http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA |
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