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vacuum tube testing

Discussion in 'Electronic Basics' started by Donald Ennis, Jun 5, 2008.

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  1. Donald Ennis

    Donald Ennis Guest

    I need some assistance with testing some 6EJ7 vacuum tubes. In the past I
    have used several tube testers which are inoperable now. I have access to
    power supplies, meters, scopes, fixtures and fixturing equipment and
    supplies. I have the specs for the tubes but I'm unsure about setting up
    the tests and interpreting the results. If anyone can help please post
    back.

    Thanks,
    Don
     
  2. Dave

    Dave Guest

    Call your local music store that advertises servicing guitar amps. Whoever
    does the work likely has a tester, or knows somebody who does.

    I picked up an old tester recently, it'll tell you good/bad, but no good for
    gain matching, it's not a mutual conductance tester.

    Or just buy one. Never heard of anybody making their own, even the
    hard-core geeks on AudioAsylum and AudioKarma don't do it, there's probably
    a reason for that...

    I saw an on-line video about Manley Labs (tube amp manufacturer) in
    California... they've got a nifty computerized rig where a computer controls
    the inputs and monitors the outputs of tubes being tested... I am sure if
    tubes were still used in large quantities such software would probably be
    available for free on the internet.

    Dave
     
  3. Dave

    Dave Guest

    Yeah, what he said.
     
  4. ian field

    ian field Guest

    Home brew CRT testers were very common in the service trade, the most
    difficult part was rigging the interchangeable bases for all the different
    CRT types.
     
  5. Donald Ennis

    Donald Ennis Guest

    Ok. A big thanks to everyone for the replies. I have done this before
    about twenty years ago but I had the help of an older gentleman who knew
    tubes very well. I had notes on how to test tubes using the mfr. specs and
    how to interpret the results but can't find them now. Once again I
    appreciate your comments and thanks for your help.

    Don
     
  6. neon

    neon

    1,325
    0
    Oct 21, 2006
    the bottom line is this any tester can surely tell you that is bad but cannot tell you how bad, Can tell that is good but will never tell you how good it is. how can it do it it all depends on the actual application. that goes for any tester
     
  7. Donald Ennis

    Donald Ennis Guest

    Thanks Stephen. This is what I'm attempting to do. I have been varying the
    control grid voltage from -2 volts to -3 volts while keeping screen grid at
    200 volts. Supply voltage (B+) is 350 vice. Plate resistor is 15K and Grid
    is coupled to ground with 10K resistor. According to the curves for pate
    current vs. control grid volts I should be getting 10 ma plate current @ 200
    volts plate voltage with -2.5 volts at control grid. What I'm getting is
    about 187 plate volts and 16 to 17 ma. plate current at this point. On some
    of the tubes the current goes quite high and the plate voltage drops to
    around 120 vdc with the control grid @ -2vdc. When I change the control
    grid voltage to -3 vdc the plate current sometimes drops off sharply to ua
    and the plate voltage climbs to around 260 and 280 vdc (I'm doing this from
    memory). To me it appears that the tubes are bad but I'm not quite sure how
    to interpret the measurements. Any thoughts on this?



    Thanks,

    Don
     
  8. Donald Ennis

    Donald Ennis Guest

    Thanks Nick, what a great site. I'll have to take some time and look it
    over.

    Don
     
  9. neon

    neon

    1,325
    0
    Oct 21, 2006
    tubes unlike transistors are dependent on cathode emission that goes with cathode voltage. they deteriote with time and without current trough they actualy go to sleep in never never land old computer had that problem sleeping sickness. they are current amplifiers as opposed to voltage amplifiers like transistors. best thing stick into the actual circuit and see.
     
  10. Baron

    Baron Guest

    Donald Ennis Inscribed thus:
    What a fascinating web site ! I would also like to offer my thanks to
    OP for bringing it to my attention.
     
  11. Rich Grise

    Rich Grise Guest

    On Fri, 06 Jun 2008 22:07:03 -0400, Donald Ennis top-posted:
    [top-post repaired below]
    It sounds like it's operating properly - do this with some graph paper
    and the curves will look very much like the ones in the book, depending
    on how they're arranged.

    Good Luck!
    Rich
     
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