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Require testing of valves

Discussion in 'classic' started by lilolee, Jan 14, 2021.

  1. lilolee

    lilolee pfm Member

    I'm in Maidenhead and I have about 100 valves I'd like to have tested.

    Obviously I can't travel until lockdown has been eased, but can anybody help?
  2. Vinny

    Vinny pfm Member

    What type of valves?
    Test for what?
    Preamp valves, basically double triodes, can be usefully tested for heater continuity (using a multimeter), but not much else, unless you just want some numbers to be able to sell them.
  3. lilolee

    lilolee pfm Member

    Yes I will be selling them so want to make sure they are OK for the buyer.

    Mostly double triodes, but also specilifically some KT66, EL34 and various rectifiers.
  4. Vinny

    Vinny pfm Member

    Providing numbers for double triodes - Gm etc. - will make them more easily sold, but the numbers mean nothing, so expect a few complaints if selling that number.

    I have bought VERY few used double triodes - probably less than 20, maybe less than 10 (lots of genuine NOS though). Of the 10-20, one Mullard was a dud but had acceptable numbers, which I did not doubt or challenge.
  5. david ellwood

    david ellwood Kirabosi Kognoscente

  6. lilolee

    lilolee pfm Member

    Yeah I might just list the Double Triodes.

    I would like the numbers for the Power Tubes though.
  7. Vinny

    Vinny pfm Member

    If you still have an amp' to test them in, that would be a better test than any valve tester, and ought to be about as slow/quick to use. At least you could throw out the definite duds, if there are any.
    That said, even valves testing low on valve testers, but of the "right" brand/vintage, still sell for good money when listed as such.
  8. Radfordman

    Radfordman pfm Member

    About 10 years ago I bought a cheap Chinese single ended EL34 amp, good for testing EL34's for my Radford STA25 III.
    Vinny likes this.
  9. brecklandboy

    brecklandboy pfm Member

    If the valve tester uses information contained in the original valve manufacturer's data sheets as the basis for setting the test parameters, then 'the numbers' would certainly mean something in establishing the relative goodness of a valve in terms of emissions or mutual conductance, for example against an expected value specified for a 'new' tube.

    Some people might enjoy the thrill of playing 'Russian roulette' by substituting untested valves in audio equipment but others may prefer to take a more cautious and measured approach.
    Darmok likes this.
  10. Vinny

    Vinny pfm Member

    Not for double triodes. I repeat here merely the received wisdom of Jez and one or two posting here who actually used valve testers as part of the everyday jobs back in the day. Continuity checking the heaters - fine, anything else, meaningless, especially so in hifi amps.
  11. Radford Revival

    Radford Revival pfm Member

    Valve testers definitely can be useful - a completely shot valve will 'work' in a hifi circuit but the performance can be slightly or massively degraded in ways that might not be immediately obvious. A tester will spot that quite readily. They will also show heater-cathode leakage which can degrade performance (usually AC heater breakthrough). They can also spot worn or tired valves. Admittedly I'm spoiled with a VCM-163!

    The numbers aren't completely meaningless - on a good tester they are a static reading of Gm and current at a specified operating point. It's not absolute by any means but a batch of valves tested on the same meter can be compared quite well. Comparison with the nominal value does indeed generally correlate quite well with wear / valve age too - a tired valve will quite clearly show itself. Not just with its reading but you get a feel for these things as you can see the current/gm rise in real time as the valve warms up, duffers tend to come up far more slowly.

    A valve tester isn't really a "valve = good or bad" tool, it's more of a test jig
    Darmok likes this.
  12. lilolee

    lilolee pfm Member

    Good idea, I might have to resurrect an old pair of monoblocks I have, based on a Leak TL25+ circuit.
  13. brecklandboy

    brecklandboy pfm Member

    We'll have to agree to disagree on that one, Vinnie.

    Valve testers are not infallible but they can certainly be a very useful tool. I don't think AVO, for example would have managed to sell tens of thousands of testers over several decades to satisfied customers including professional and military users who were somehow deluded into thinking that the results they produced were accurate and meaningful.
  14. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    I use valves in my work all the time and although I can get a free AVO or Mullard valve tester if I want one I don't have or ever use any form of valve tester (and I'm a vintage test gear junky!). Nor would I take any notice of figures derived from one.
  15. lilolee

    lilolee pfm Member

    That was hearty guys, but has given me food for thought.

    I'll be able to get the power tubes tested, once lockdown has eased, and I'll juryrig a setup to test the heaters for continuity. As I said I will be selling these on, so don't want to sell anyone a dud.

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