Can I Test Old Vacuum Electron Tubes a simple way? - Page 3
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  1. #41
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    Quote Originally Posted by JST View Post
    The problem with tv tubes is not being tested for noise, or even being designed for low noise or low microphonics.

    Idea sounds good, works out less well.

    There is a 6C4 in certain Ampeg SVT bass amps, which causes a noise problem even though it is not in any way high gain. Just never designed for that use. No problem in radio use.
    This hardly seems the place for detailed electronic design discussion and I'm NOT a provocative person but here's a couple of thoughts:

    My book describes in detail (including machining the chassis and the cabinet) the design and construction of a compact vacuum tube amplifier with similar performance characteristics to the Fender Bassman, using a pair of TV tubes for the output stage. No microphonic problems, no noise problems. (It's actually quieter than my vintage Bassman.

    The tubes in the output stage of any amplifier contribute virtually nothing to amplifier noise, which is primarily established in the preamplifier stage. The main problem is not noise but hum suppression, a function of layout and power supply filtering, not tube design (provided that indirect heated cathodes are employed). Noise is discussed in the book with means of estimating it.

    I make no comments whatsoever regarding the use of TV tubes in a preamplifier application. (I suspect however that I could find a number of them that would work just fine.)



    I am currently designing an inline preamplifier for accoustic guitar using acorn tubes originally constructed and screened for proximity fuse circuits in artillery projectiles, a tough shock and microphonic environment ! Just happened to see them on eBay and picked them up at a reasonable price. Interesting project with several challenges.

    Quote Originally Posted by The real Leigh View Post
    And I'm confident it's worth every penny.

    - Leigh
    I assume that you read the 350 some pages of the book in the last hour or so and are therefore an authority on it's content ?

    If not, your sarcasm seems inappropriate. I suspect that you know little about this subject - if you did, your comment would have some substance rather than your cheap shot. Shame on you !

    I think that J. Tiers has a background similar to mine so I take his comments seriously enough to respond seriously

  2. #42
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    I am sure it CAN work.... But, there is an issue with using "off data sheet" specs, because they are not on the sheet, they are not in any way guaranteed. Like audio band noise in a tube usually used in an FM IF stage...

    Even standard 12AX7 have only a rudimentary noise spec, if any. But noise is not the only possible issue.

    We did find MIL 6C4 that worked in most cases for the SVT, although MIL does not imply higher quality, just a different set of specs.

    As a side point, I have an old Genrad noise meter which uses not the acorn tubes, but the small rectangular tubes about 5mm x 10mm x 30mm. obviously they thought it would be OK, and they were trying for a decent low noise preamp. IIRC those tubes were not spec'd for noise, although I'd have to look up the manual to see the type, and then find a tube manual with the specs for the types IN it.... that was a newer innovation, my manuals are older.

    Tubes were usually reasonably quiet in general, but not always. We had them sorted for very low noise for preamp first stages, etc.

    The biggest problem is high plate resistance, leading to high plate load resistors, and consequent noise issues, not to mention high input res, same result

  3. #43
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    Quote Originally Posted by JST View Post
    I am sure it CAN work.... But, there is an issue with using "off data sheet" specs, because they are not on the sheet, they are not in any way guaranteed. Like audio band noise in a tube usually used in an FM IF stage...

    Even standard 12AX7 have only a rudimentary noise spec, if any. But noise is not the only possible issue.

    We did find MIL 6C4 that worked in most cases for the SVT, although MIL does not imply higher quality, just a different set of specs.
    Again, I don't like to be provocative but "CAN work" is incorrect, it "DOES" work.

    Perhaps it wasn't clear that the TV tubes to which I referred are employed in the amplifier OUTPUT stage. The specified data sheet noise, even the actual MEASURED noise, is trivial - output stage noise is insignificant in almost any amplifier, from 10 Hz to 40 GHz, if the preamplifier gain is more than 15 or 20 dB.

    Insofar as preamplifier tube noise is concerned, only the first tube is of importance. Terminate the input, max the volume control, measure the output noise at the speaker terminals with a sensitive VOM. Substitute a few 12AX7's (or whatever) for lowest noise voltage and Bob's yer uncle.

    A noise generator is also helpful and can be constructed with two transistors, a zener diode and a couple of resistors. The circuit schematic can be supplied to any interested person. (Circuits for the power amplifier discussed as well as the high voltage power supplies used for testing are included in the book.)

    I keep a half dozen preamp tubes on hand for the noise exercise. Often an amplifier will employ up to three of the same tube as the preamplifier stage so trial and error with existing tubes will produce the quietest configuration - no need to buy anything. This procedure is also described in the book.

  4. #44
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    OK....

    Input AND the stage after passive EQ.... High Z, and reasonably high gain also.... But again, the issues with noise are usually grid impedance related... can be a combo of that with a leaky grid, or tubes without good heater leakage specs.

    But if you are not doing the preamp that way, then the issues are lots less, outputs is outputs. Ham radio folks have been using TV sweep tubes as finals for decades. They are just tubes and do work.

    Sometimes you get a noise like rattling chains from output tubes directly. I don't recall what we traced that to, must have been a form of microphonics, and so related to loose mica most likely.

    Seemed like the idea was more subs than just finals at first. I didn't read the book, so.....

  5. #45
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    Quote Originally Posted by JST View Post
    OK....

    Input AND the stage after passive EQ.... High Z, and reasonably high gain also.... But again, the issues with noise are usually grid impedance related... can be a combo of that with a leaky grid, or tubes without good heater leakage specs.

    But if you are not doing the preamp that way, then the issues are lots less, outputs is outputs. Ham radio folks have been using TV sweep tubes as finals for decades. They are just tubes and do work.

    Sometimes you get a noise like rattling chains from output tubes directly. I don't recall what we traced that to, must have been a form of microphonics, and so related to loose mica most likely.

    Seemed like the idea was more subs than just finals at first. I didn't read the book, so.....
    So read the book At least read the section dealing with design outline, tube selection, how to bias the screen grid for optimum performance even if the tube APPEARS to be inappropriate for the application.

    Good night.

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    Quote Originally Posted by randyc View Post
    I suspect that you know little about this subject - if you did, your comment would have some substance rather than your cheap shot.
    I've only been working with tube circuits for 57+ years, so I have a lot to learn.

    My earlier comment about TV tubes being just about worthless is based on the selling price thereof, and the fact most tube dealers won't buy them. There are still millions of them in the pipe. I noted two recent sales, one for a million tubes, and the other for about 3/4 million. They went for less than $0.10 per tube.

    Horizontal output tubes are the exception. Those have been used in ham transmitters for many decades. They are still usable in amplifier output stages, as you apparently did in that one. A power tube is a power tube. As you observed, internal noise is not an issue since it is much lower than the applied signal.

    As to "reading the book"...
    I have read the Radiotron Designer's Handbook (4th ed) almost completely several times. I take that as my authoritative reference.


    - Leigh

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    Randy, a non life threatening quibble- the tube on the left is what we always called an acorn tube. AFAIK, the VT fuse used what I have always called subminiature tubes. Jerry, does your meter use tubes like the one on the right? I have never seen anything that used them.

    RE "audiofools" I am a former tube collector who has reached the stage of life that my relatives are urging me to reduce my inventory, so the tubes are going on EBAY and to John Walker. Eitel-McCullogh made a tube originally as a radar pulse tube designated 304T, apparently only for a short time, replaced by the 304TH and 304TL, high and low amplification factor. There was a pair of 304Ts on EBAY but I was outbid. I contacted the winner and asked if he would sell me one for my collection. He replied that he needed both because he was going to build a two channel audio amplifier, patterned after one on the market. If he is only using one per channel, they must run in class A and the 304T curves indicate that it would be a terrible class A amplifier unless you used an extreme amount of feedback. As a measure of the fellow's expertise, 304s need 125 watts just to light the filaments and run at full power dissipate 300 watts in their plates, making a total of 850 watts in one box. He asked if I thought he should use a cooling fan. Duh.

    BTW when I was a teenager, surplus 304s were $5, so I could afford them on a hamburger stand carhop's pay. I had a 304TH in the final of a 40 meter transmitter modulated by a pair of 304TLs in AB1. That was the first I actually got compliments on my signal.

    Bill

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    Forgot the picture, just the beginning of my impending senility.
    Attached Thumbnails Attached Thumbnails acorn-tube.jpg  

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    Glad to see some other ham operators here !!

    KD8QHS

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    I just listed them...you guys can fight over them now.....lol
    Attached Thumbnails Attached Thumbnails 20150815_085017.jpg  

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    Quote Originally Posted by Richard King View Post
    I just listed them...you guys can fight over them now.....lol
    I'm out.

    There ain't even ONE proper four-pin 2A3 triode in the whole dang lot, let alone pairs or foursomes.


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    I was expecting a quad of 300Bs, but no such luck.

    I woulda paid gud muny, like ten bux apiece.

    - Leigh

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    Quote Originally Posted by The real Leigh View Post
    I was expecting a quad of 300Bs, but no such luck.

    I woulda paid gud muny, like ten bux apiece.

    - Leigh
    Be fair. I don' think Rich is even 70 yet, so he'd ha' missed the whole era of the Good Olds...



    BTW - there's folks out there in ebay-land asking $300-$400 for 2A3's.

    Never wudda predicted it back when they were driving RCA's "Voice of the Theatre' 15-inchers all over small-town America.

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    Not like that flat tube, no, these have all leads at one end. I'll see if I can get a picture. I have some spares of them also.

    Never actually seen that flat tube before, read about it, IIRC. Acorns and Nuvistors, yes.

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    Quote Originally Posted by Torpedoheat View Post
    Glad to see some other ham operators here !!

    KD8QHS
    W0WLW here

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    Quote Originally Posted by Yan Wo View Post
    W0WLW here
    Don't lets' start. Three of my 'mentors' - all long-gone - pre-dated the birth of the FCC and held callsigns with but four characters to them. In total.

    I never went that route. 'Day Job' was too intensive arredy to want to see any more of the technology once off-watch.

    SWL gear OTOH? That's how my Spanish gained the selectable accents - Cuban, Ecuadorian.... etc..

    Listen to 'enough' variety of foreign-language sources? Or nowadays read them online?

    Welll.. you aren't REALLY all that likely to buy-in to 'propaganda'.. less-so, actually, the more you explore.

    But it sure does help figure out that OUR media is playing-silly-buggers ALSO.

    And that Congress has a lot to answer for in EITHER party.



    Bill

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    Quote Originally Posted by The real Leigh View Post
    I've only been working with tube circuits for 57+ years, so I have a lot to learn....

    ...I have read the Radiotron Designer's Handbook (4th ed) almost completely several times. I take that as my authoritative reference...
    First: Sorry, Richard, for getting so far afield from your thread !

    "Working with tubes" for however many years does not imply any expertise in the field. (My own experience slightly exceeds 57 years but more importantly I understand how to use vacuum tubes and how to design effective, practical circuits without copying decades-old designs.)

    As far as your "authoritative" (sic) reference is concerned, I fail to see how it has any bearing on your post. Your cheap shot concerned MY book and your "authoritative" reference has no bearing on the discussion.

    Since you have no knowledge of my book, your comment makes as much sense as stating that you've read a book on medicine and all other medical books are worthless.

    I had no desire to start a pi--ing contest, as I implied in several posts. But when you assign a value of zero to months of my work, then I feel that I must respond !

    P.S. You might want to search the internet to see how others regard the book -

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    Quote Originally Posted by randyc View Post
    First: Sorry, Richard, for getting so far afield from your thread !
    Perhaps we should ALL stop..

    I had a landlord for a time that played lead in a Rock Band, but also taught classical acoustic guitar, formally, and at the University level.

    While hearing "Malaguena" rendered on a Fender Jaguar was, at the time, impressive enough, I already had anechoic chamber instrumentation well behind me, so..

    Use of an entertainment-grade amp as an example of your expertise just doesn't draw much interest among those who have covered far the wider spectrum of vacuum-state applications and whose pubs about that covered defense systems that were 'classified' at the time.

    'Lack of interest' does not equate to 'disrespect'.

    But it as arrogance makes a poor 'getter' it could become that.

    Lighten up....

    Bill

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    Quote Originally Posted by thermite View Post
    ...Use of an entertainment-grade amp as an example of your expertise just doesn't draw much interest among those who have covered far the wider spectrum of vacuum-state applications and whose pubs about that covered defense systems that were 'classified' at the time...
    BUT, left unsaid (until now) is my over forty years of experience as a design engineer in the Telecommunication, Defense and Aerospace industries, designing hardware from D.C. to 40 GHz.

    After retiring from Silicon Gulch and until sidelined by lung cancer, I operated a consulting engineering business from my home. The infrastructure of the business still exists, complete with a well-equipped machine shop (for constructing proof-of-concept hardware) and electronics lab for verifying performance. (FWIW, part of the lab can be seen on the cover of my book.)

    Cancer required that one of my lungs be removed and with nothing to occupy me, my wife bought me a laptop that I could use in bed, encouraging me to write the vacuum tube book during my recovery.

    (My resume is available upon request should anyone need advice, analysis, software support and so forth on systems architecture and component design, ha-ha-ha )






    Didn't bother to blank out my name since it's on the book anyway. As far as letting this conversation die a natural death, I'm still pi--ed at the cheap shot but willing to say f--ck it and get back to doing something of significance !

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    Quote Originally Posted by randyc View Post
    BUT, left unsaid (until now) is my over forty years of experience as a design engineer in the Telecommunication, Defense and Aerospace industries, designing hardware from D.C. to 40 GHz.
    All well and good, but all that does is make you a 'Well Qualified' arrogant <epithet of choice> on-record.

    It does not make anyone else LESS of... either of those, actually.. Nor does anyone here claim the patent on either..

    WTF... Fifty-thousand openings for rude buggers going unfilled in the telemarketing industry alone...and you want to be a vacuum-tube expert?

    Go figure...



    Bill


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