Trust you tester / meter?

Discussion in 'General Electronics Chat' started by Gdrumm, Sep 29, 2014.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I'm delving into antique radio repair as another hobby, and one of my first ones is a shortwave Spartan 6A66. I've replaced all the caps, except for the Filter Cap, which I finally figured out how to re-stuff this weekend.

    I bought an old vacuum tube tester from ebay, and all of the tubes except for one are testing bad.
    I believe they are 7 pin (larger fatter tubes, like 35z5gt, 35l6gt, 12sq7gt, 12sk7gt).

    On my 3 other old AM radios, I tested all the tubes (I believe they are 9 pin) (smaller tubes), and they all tested good.

    Should I trust the tube tester?
    Is there a way to test the tubes with a multimeter?

    Thanks,
    Gary
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the only test on tubes with a multimeter is to test for a filament contnuity. possably measure viltage in set under power, thats about it. most multimeters dont have enough voltage to test for gas or conduction.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Not really easy with a meter unless you set up certain test voltages.
    Way- way back I built my own tube tester, even wound the transformer to cover all the different filament voltages!
    I still have the copy of Radio Valve Data that covered the characteristics of 7000 tube types. (UK 9/6d).
    Most tube testers should give you a ball park figure, like anything probably some are better than others.
    They must be getting rare now though?
    Max.
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    As said, you can check if the filament is OK.
    Also you could check for shorts between the elements in the tube (cathode, grid, anode).

    Here is a page that might interest you:
    http://www.nj7p.org/
    You will find a lot of tube data over there.

    Bertus
     
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  5. #12

    Expert

    Nov 30, 2010
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    I quit trusting tube testers when a peanut size RF amplifier tested good with a crack in the glass and the getter gone all white.
    Just swapping out the tube was the gold standard from 1950 to 1970, but that isn't so easy in the 21st century.
    Now, you need to understand what each tube is supposed to do and check to see if it's doing it.
    Easier said than done! Just trying to measure the circuits with a 10pf probe will throw some of them off.
     
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  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    you can use your meter to check all those old carbon resistors. Replacement of those might be needed. They drift off value quite a bit. The female pins in the tube sockets could probably use a good cleaning as well.
     
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  7. RichardO

    Well-Known Member

    May 4, 2013
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    Excellent idea. I would clean the contacts in both the radio and the tube tester.
     
  8. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Good thoughts, and cleaning might make a big difference.
    Awesome Tube lookup link as well.

    And for the other tips,

    Thanks all,
    Gary
     
  9. #12

    Expert

    Nov 30, 2010
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  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Largest tube I have worked with had a 3Kw cathode htr.
    Max.
     
  11. #12

    Expert

    Nov 30, 2010
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    Canada is a good place to work on 3KW tube heaters. You can comfortably heat the room with them! :p
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Actually it was in the UK, H.F. 450Khz equipment, silver soldered the filler pipes in the Austin/Morris Mini gas tanks.:cool:
    Max.
     
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