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Trouble with Bias on my Ampeg Classic head

Discussion in 'Amps and Cabs [BG]' started by tim_wilson_, May 7, 2010.

  1. tim_wilson_


    Mar 11, 2007
    I am having trouble biasing my ampeg svt classic head. I thought it was old tubes so I replaced the power amp tubes but I still can't get it to bias on the left hand side bias control. It goes from nothing straight to red and never touches the green. Does anyone have any ideas on this? I would be very grateful.
  2. Fault with the bias supply. Take it to a tech.

  3. +1 Also bad driver, support componets.......tech time.
  4. username1


    Dec 28, 2005
    alberta canada
    I would try switching the 3 inside tubes around with the outside ones and see if the same thing happens with the other bias light and if that one will go green after the switch. I have had new tubes that wernt matched well and had the same problem and by switching them around the problem showed up on the other bias lights telling me it was the tubes at fault.
  5. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    If the other side biases OK then the bias power supply is OK. You could as suggested try swapping the output tubes side to side, but it also might be worth it to try swapping just the driver tubes by themselves as a second test.

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