Trouble with Bias on my Ampeg Classic head

[tim_wilson_]

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.

[BassmanPaul]

Fault with the bias supply. Take it to a tech.

Paul

[B-string]

Originally Posted by BassmanPaul

Fault with the bias supply. Take it to a tech.

Paul

+1 Also bad driver, support componets.......tech time.

[username1]

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.

[okcrum]

Originally Posted by tim_wilson_

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.

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.