Would a bad tube cause this problem?

Discussion in 'Amps and Cabs [BG]' started by BLU Dragon, May 27, 2002.

  1. I just picked up a used amp from ebay that I'm plannin' on gigging with. It's an SVT III, which seems to be the predecesor of the SVT 3R. Used it for a single set at an "open mike night" that my band hosted on Thursday. Everthing seemed O.K. on Thursday. But then, played a full gig (four hours) on Saturday and the power level seemed to fade in and out. Not a lot, but noticably. I could compensate by just digging in harder on the bass. However, I was playing with it some today in my basement and it started cutting out all the way. Cords are new. Tried two different basses. Speaker cabs have worked recently with another amp. Could this amp need to be retubed, or is there something else going on?

  2. chucko58


    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    Could be tubes, could be dirty connectors in the effects loop, could be dirty controls. Get some good contact cleaner (I like the Caig Labs stuff, http://www.caig.com/) and hit anything mechanical that passes an electrical signal - and yes, that includes the tube sockets.
  3. bben


    Feb 28, 2002
    Santa Fe, NM
    FWIW, after chucko's list, the thing that next-most-often goes wrong with tube amps is capacitors, but usually you get noise or hum with a bad capacitor, not a fade-out.
  4. jokerjkny


    Jan 19, 2002
    NY / NJ / PA
    could be any number of things, but definitely seems transformer related. i'd have a tech take a look to save yourself the electro shock therapy. :eek:
  5. Thanks for the suggestions, guys.

  6. Please note: A further discussion of the problem with this particular amp has been continued on the thread "Gigging with a Tube Amp."

  7. I seem to remember reading somewhere that power tubes can cause that (among other things) when they get weak. It couldn't hurt to have them tested.
  8. Rockbobmel

    Rockbobmel Supporting Member

    I believe the SVT III is a tube pre/tranny power amp head. I know the SVT III Pro is. If that's the case, then you won't have any power tube problems.
  9. That would be correct, sir. Three 12ax7's in the pre, and the MOSFET power amp section from the B2r (or the SVT H). So, it's not a power amp tube. Further adding to the mystery, it seems to only have been giving me trouble when I run it into a four ohm load. Yesterday, when I unplugged one of the 15's -- no problems. Again, please refer to the other thread on "Gigging with a tube amp", where this discussion has been continued.