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Ampeg B-1 R with tube-pre puts out for 5 minutes then dies

Discussion in 'Amps and Cabs [BG]' started by Band Dad, Jul 22, 2012.


  1. Band Dad

    Band Dad

    Dec 5, 2006
    San Mateo, CA
    Is this a tube issue? Or is there another component that would cause this?

    I bought the amp with the caveat that after a few minutes playing it would die. The seller said it had something to do with the volume.

    I bought the amp, used contact cleaner (as best I could; the pot is rather well sealed), then tested for a few minutes with no problems. I thought I'd fixed it.

    Then I sold the amp a week ago, never having really used it. The buyer just called and described the same symptoms the the person who sold it to me described.

    I'm now offering my buyer his money back, but need to fix this issue in order to sell the thing.

    Any ideas? Bad tube? Do bad tubes cause problems like this? It's an on and off thing in that it will power up and play, but will, consistently, apparently, die after a few minutes use each time. Capacitor? Diode? (I'm grasping at straws here, I know). Thanks.
     
  2. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Could be as simple as a clogged cooling tunnel or corroded switches in the FX loop jacks. Try linking the FX Send and Return with a signal cable.
     
  3. Band Dad

    Band Dad

    Dec 5, 2006
    San Mateo, CA
    I'm not sure what a cooling tunnel is, Paul. Could you explain? It sounds like you're suggesting that this might be a problem with overheating.

    And with the effects loop. Are you saying just plug a cord into the send and return in order to either bypass something, or, by use, clean the contacts?

    I appreciate the help, Paul. Unfortunately, I don't have the amp to try these solutions on. The buyer has it, and he's about two hours away. I'd pass along any info I might gather and hope he's game to give it a try.

    Ian
     
  4. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    In a fan cooled amp air is blown across the fins of the heat sinks to cool them. Over time these can become clogged with crud and can't be effectively cooled. Periodically it's good to vacuum the amp out to restore the cooling efficiency. I had a Peavey once that would do just as you described. It was filthy inside. After the cleaning the amp worked perfectly.

    In a series effects loop when there is nothing in the jacks they are shorted together by switches built into the jacks. These can become dirty and corroded and the signal fails to pass through. By linking the Send and Return the switches are out of the circuit.
     
  5. Band Dad

    Band Dad

    Dec 5, 2006
    San Mateo, CA
    Thanks, Paul. I've just recommended to my buyer that he try the effects loop test. If that fails, he'll return the amp, which will at least have it back in my hands where I can personally make attempts to fix the problem.

    I don't recall anything in the way of crud in any parts of the amp. But then, I'm envisioning all sorts of crusty buildup and such when I think "crud". If what you mean is a light coating of dust, well, then I may notice something.

    In this amp, the fan is just drawing air through the general cavity of the insides. There is a finned heat sink that the cover plate screws to inorder, I would think, to increase the surface cooling area of the heat sink.

    Now, just as I'm writing this, the buyer called to say that he tested the effects loop with a patch cord and the problem remains.

    Looks like I'll have the machine back to more closely test and monitor (and hopefully fix). I'll post my findings.

    Thanks!

    Ian
     

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