HELP!!! Amp (DRRI) not working properly

Discussion in 'Amps and Cabs' started by johann, Mar 3, 2012.

  1. johann

    johann Member

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    Help please.

    My DRRI gave me some troubles last night.

    First when I was plugging everything, I turned it up to warm it, and it began making a feedback (not too loud) without anything plugged on it, I plugged in and it still made that feedback (only on channel 1, both inputs) channel 2 worked nicely.

    So I used channel 2 the whole night,

    BUT....

    I noticed some drop on the overall volume, second set I plugged on the channel 1...no feedback, but low volume, I normally play with volume on 3 1/2, last night I was playing at 5!!!

    What's wrong with it???


    HELP ME PLEASE GUYS
     
  2. windjamma

    windjamma Member

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    check v1 and other tubes, sounds like a microphonic tube.
     
  3. johann

    johann Member

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  4. johann

    johann Member

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    just one question, how can I check for a microphonic tube???
     
  5. tbblues

    tbblues Member

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    One by one, tap each tube softly with a wooden chopstick or similar item. Microphonic tubes will ring or squeel. Don't use anything metal like a screwdriver.

    OR, one by one, replace each tube with a tube of the same kind. If the problem goes away, then that was the offending tube. Often, in DRRIs the power tubes will go since the amp is biased hot.

    Sometimes, visual inspection of the tubes with the amp on reveals one that is glowing excessively and is perhaps ready to fail. Be careful, warmed-up tubes can be very hot and can burn you.

    If you are not comfortable poking around the innards of your amp, be prudent and enlist the help of a tech.
     
  6. johann

    johann Member

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    mmmm and how about a tube with some kind of blue aura???
     
  7. windjamma

    windjamma Member

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    blue aura in power tubes is normal me thinks but i am not tech savvy
     
  8. johann

    johann Member

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    OK, I tapped each tube, 3 squealed, one of the power tubes did a kind of loud THUMP and a CRACKLE, so I guess they're bad.

    I found some JJ tubes in a store here in my city, I want to change them, do I need to adjust the BIAS????
     
  9. mhuxtable

    mhuxtable Member

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    Preamp tubes don't need any biasing, just plug and play.

    Power tubes do need to be biased, and if you don't know what you're doing, take it to a tech.
     
  10. johann

    johann Member

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