Volume going up/down.... bad tube?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Scott Peterson, Sep 13, 2005.


  1. Scott Peterson

    Scott Peterson Staff Member

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    I am a little befuddled.

    My VHT Pittbull 50/ST head (tube rectified, EL34's output) sounds great... but it has started to do something wierd.

    The volume will just "go away" down to almost a whisper and then surge back up and it does this till I shut it off in fear it is about to blow.

    Bad tube? Bad rectifier? Initial things to check?
     
  2. RL in Fla

    RL in Fla Member

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    Recto first Scott , since there's only one of em , if not that a tube at a time from V1 on up .
     
  3. Scott Peterson

    Scott Peterson Staff Member

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    I figured as much. Gotta wait till tomorrow to fire it up and have at it.

    Thanks!!!
     
  4. RL in Fla

    RL in Fla Member

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    Somebody will chime in and tell me I'm full of crap (BIG news flash there :D ) , but that's what I'd guess .
     
  5. Scumback Speakers

    Scumback Speakers Gold Supporting Member

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    You're full of crap RL! (Feel better?) :D

    Actually, tubes are a good place to start. It gets more expensive if it's not that. I have a Studio 15 doing the same thing. Works great for 5 or 10 or even 30 minutes, then it starts doing an elevator volume thing, but then it goes down to a whisper, then nothing.

    I shut if off, it cools off, then it's fine the next time I fire it up...for 5 maybe (wait this is a repeat, huh?) 10 minutes then the same thing happens again.

    Swapped all the tubes. That wasn't it. I'm at the more expensive fix. Good luck, Scott! (RL, you're not really full of crap...)
     
  6. RL in Fla

    RL in Fla Member

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    Big news flash !!! Film at 11:11 !!!!!!! :D :D :AOK


    Yours may be a solder joint -
    heating up/losing contact/cool off/ ok again Jim .
    Not you , the amp . :D :D
     
  7. VaughnC

    VaughnC Supporting Member

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    Yup, most likely a tube or solder joint. Also, if you have a bias probe that also displays the plate voltage on the output tubes, if that voltage lessens with the corresponding volume drop, the rectifier tube would be a good suspect.
     
  8. Scott Peterson

    Scott Peterson Staff Member

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    Well, you were right. Thus far, no more volume swells by itself; rectifier tube.

    Thanks!
     
  9. RL in Fla

    RL in Fla Member

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    Right 1 Wrong 5,732,435

    :D
     

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