How do you diagnose a bad tube?

Discussion in 'Amps and Cabs' started by Crowder, Dec 26, 2009.

  1. Crowder

    Crowder Dang Twangler Silver Supporting Member

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    I recently bought an unused Tone King Imperial and I think I have a bad tube.

    The amp functions normally from start-up through the first twenty minutes of playing. At that point, I hear some brief static from the back of the amp, and the signal fades to a fizzy, low-power mode where I can hear everything I'm playing. Any effects on at that time are enhanced (verb or trem). I can still switch channels, etc, but the tone sounds like the last vestiges of sound you hear when you switch an amp to standby while playing. Turning the amp off for a cool-down period starts the cycle all over again.

    I've swapped a few preamp tubes around and the issue has improved some....today there was one episode of the problem happening very briefly then going away again. I'm pretty sure one of the five 12AX7's is balky, but due to the comes-and-goes nature of the problem, I'm not sure how to isolate the bad tube.

    Any ideas?

    And, of course, any suggestions on where to buy good tubes?

    Thanks,
    Mike
     
  2. riffmeister

    riffmeister Gold Supporting Member

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    It's new? Call or email Mark, he will take care of you.
     
  3. GuitarBrent

    GuitarBrent Member

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    with the amp on, slightly tap on each tube to see if one is going microphonic or bad...you will hear a drastic difference if one is...
     
  4. Crowder

    Crowder Dang Twangler Silver Supporting Member

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    That's definitely in the cards for the day off I'm taking Monday. I've heard nothing but raves about his pride in his product, so I'm not concerned about that.
     

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