Is the OT on the OUT..?

Discussion in 'Amp Tech Center' started by Jeru, Sep 6, 2019.

  1. Jeru

    Jeru Tele-Holic

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    This is a friend's amp, a vintage Teisco Checkmate.
    The last time the amp was on was when this video
    was taken, and only then turned on for the purpose
    of quickly documenting the problem.

    I have built a few amps, and I generally understand
    what the OT does and how it works, but what's going
    on here is above my pay grade other than to say that
    when loud chords are played, the OT seems to be be
    internally arcing or shorting.



    So:

    1) What's your take on what the issue is?

    2) Is it likely internal to / limited to the OT..?

    Any opinions, input, suggestions welcome.

    Thanks.
     
  2. corliss1

    corliss1 Friend of Leo's

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    How could anyone continue to use an amp in that condition?

    Disconnect current OT, clip in some other OT, and see what happens. That's really the best way to know, but yes, it seems like something is up on the OT primary there.
     
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  3. tubelectron

    tubelectron Tele-Holic

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    1 - open the amp and look where the arcing was produced :

    - I suggest that it could be the plate wire that is uninsulated and arcs with the chassis. Check the wires of transformer primary. There's certainly traces of the arcing here...

    2 - disconnect all the wires to the output transformer (and note the wiring !).

    - Then using a DMM in the ohm function starting with the maximum megohms range, test for leaks between primary and secondary, and primary with chassis, and secondary with chassis. For a possible - but not sure - correct transformer, you must read infinite, otherwise the Xfo is insulation flashed, and thus is dead - and here, that's a certainity.

    Doing this, you'll be able to suspect or discard the output transformer.

    Of course, DO NOT power your amp anymore as is !

    Let us know the results... ;)

    -tbln
     
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  4. Jeru

    Jeru Tele-Holic

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    Thank you for your replies.

    Nobody is continuing to power on or use the amp, my friend
    last powered it on solely to take the video (paragraph 1)
     
  5. PlainAllman

    PlainAllman Tele-Holic

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    Is that one of Angus Youngs old amps, cause that gives new meaning to the idea of high voltage. :lol:
     
  6. peteb

    peteb Friend of Leo's

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    I was unsure what to think myself. This comment made a lot of sense to me:







    The fire works appear to occur externally rather than internally to the OT.
     
  7. Wally

    Wally Telefied Ad Free Member

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    There definitely is a short to ground somewhere.
     
  8. tubelectron

    tubelectron Tele-Holic

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    Yes. It may be just the insulation of the plate wire which is faulty... That said, if the OPT is not damaged, it's nonetheless in great danger !

    -tlbn
     
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