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Another what's wrong with my amp thread.

Discussion in 'Amps and Cabs [BG]' started by Nighttrain1127, Dec 24, 2013.


  1. I have a Peavey Alpha Bass head. When it is first turned on it sounds fine but by the end of the first song it is cutting volume to nothing and sounding very distorted. it eventually comes back to normal volume but continues to do the drop out thing whenever it feels like. Any quick and easy(safe) Ideas
     
  2. christw

    christw Get low! Supporting Member

    May 11, 2008
    Dayton OH
    Disclosures:
    I want to be Tesla (tinkerer at Dayton Amp Co)
    Dying preamp tube or more likely, the phase inverter. If you feel safe doing it, you can remove the top of the amp (when it's off of course!) and switch out the preamp tubes one by one to see if that solves the problem. The PI is probably a 12AX7 or 12AT7 in some random position.
     
  3. dmrogers

    dmrogers Supporting Member

    Jan 26, 2005
    Eastman, GA
    I recently experienced the same thing with my pre-amp. I also have experienced this with my older tube amp. It was a loose tube socket.

    Have you cleaned the FX send/return inputs?



    How good are you with electronics? If you are not familiar with electronics troubleshooting, you can really hurt yourself.

    If you decide to troubleshoot, be very careful.
     
  4. I used to work on High power radar 2.2 Megawatts so I am familiar with how electronics work. and cleaning the FX jacks was my first step. If it was the PI would it clean up for extended time then mess up again?
     
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  6. if i plug into the fx return jack the sound is still distorted and that should if i am correct bypass the pre section
     
  7. christw

    christw Get low! Supporting Member

    May 11, 2008
    Dayton OH
    Disclosures:
    I want to be Tesla (tinkerer at Dayton Amp Co)
    Cool! And yes, it's completely possible. That's happened to me more than once on more than one amp, including an Alphabass I once owned.

    Yep! Which leads me to suspect it's one of the two buggers in the middle row by the caps-a 12AX7 and 12AT7 IIRC. I believe them to be driver/PI and probably the source of your random distortion.

    [​IMG]
     
  8. Just was checking that the power tubes were properly seated and the the first one to the left of the fan in the picture was very hot while the rest were not even warm to the touch.
     
  9. What power tubes belong in here? it has 5881wxt tubes in it right now.
     
  10. christw

    christw Get low! Supporting Member

    May 11, 2008
    Dayton OH
    Disclosures:
    I want to be Tesla (tinkerer at Dayton Amp Co)
    I'm no good for suggestions here. Looks like the air flow wouldn't be the cause of that on its own. There are guys who know a great deal more than I who will probably chime in! I'd start checking component values though.

    5881's are very close to 6L6 which are stock of that amp.
     
  11. Thanks for your help if you think of anything else let me know . I will check back later.
     
  12. I replaced all the pre tubes except the 12AT7 can"t Find my Spare right now. It seems to be working like it should but only time will tell, I guess. Any other Ideas for things I should check out if this Issue continues?
     



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