#1
A buddy of mine gave me a mid 70's Orange OR80 that was broken. He said it kept burning out tubes. I had a tech replace the tubes, all the caps and some burned out resistors. The amp turns on but when we go to bias the tubes the meter keeps climbing real fast and wont stop.We had to shut it down after it hit 100mA. The bias on this amp should be in the 31 to 35mA range. The plate voltage is 560v. Thats normal for el34's. Any help? We are running out of ideas. Thanks.
#2
Okay, here is my suggestion. First remove the tubes. Put a voltage meter to measure DC voltage at pin 5 of an EL34's socket. Now turn the bias pot until the voltage is as negative as it will go.

If this voltage doesn't go below -17v, I'd say you may have a problem in your bias circuit. If your voltage goes down to let's say something like -25v, the bias circuit wouldn't be my first suspect.

My first suspect would be your screen resistors. I don't have an OR80 schematic, but in an OR120 they are 1K 5w resistors. They go to pin 4 of the EL34s. The screens help limit the amount of current drawn by the tube. Make sure there is no carbon built up on the sockets or near your screen resistors.