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SWR Bass 350 tube problem??

Discussion in 'Amps and Cabs [BG]' started by Mcrelly, Oct 12, 2003.

  1. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    I've had my 350 for a couple of years and have liked its 'sound' with its tube gain as high as possible without clipping. I changed the tube a few months ago and it worked fine until recently. I'm not sure if this has something to do with the tube, but you tell me what you think.

    When I plug into the passive input and turn the volume up on the guitar and amp, the volume goes slowly (every few seconds) up and down?? and if I watch the speakers the cones slowly push out and in when the note is playing. almost like the zero line of the wave is moving up and down?? after I'm plugged in for a few minutes its stops?

    if I run through my RBI (solid state) and return into the power section of the SWR every thing sounds good and stable.

    On a minor point there is a buzzing when plugged into the swr, but that maybe a ground looop from the DI wire plugged into the RBI output.

    any ideas?
  2. i'm in no way an expert on this, but it almost sounds like the amp doesn't have enough power...
  3. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    No, I'VE NEVER heard this strange problem on my amp before. its like someone is s-l-o-w-l-y turning the volume up and down every few seconds then I play with the wires and the gain knob a bit and it stops?
  4. and how long has it been doing this?
  5. Mcrelly


    Jun 16, 2003
    Minnesota, USA
    only the last couple of weeks. when you say power do you mean power supply? well, again during this time I've mostly been using the power amp section and goin through the RBI as the preamp. coming into the swr effects return.
  6. Bad input jack or cable? Never heard of a tube going bad that quickly, but you could try swapping it out with your old tube.
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