You question is not clear to me? When you change the tube does the problem move with the tube? Example V1 flickers and is distorted and you move that tube to say the V5 position. Does the problem move to the V5 position or does the V1 position still have the problem?
Which tube is it? KT88, 12at7 or 12ax7? If it is only one position that causes the problem you have a few things you can do. Make sure the pins are all bent so they make connection and the tube is seated well. If that doesn't fix it you will need a tech.
It will be a simple problem. Not much to those amps. A couple resistors or a cap. Could even be a pinched wire touching the chassis. The power supply is shared by both channels so I don't think that is your problem. Anyway good luck.
Which tube is it? KT88, 12at7 or 12ax7? If it is only one position that causes the problem you have a few things you can do. Make sure the pins are all bent so they make connection and the tube is seated well. If that doesn't fix it you will need a tech.
It will be a simple problem. Not much to those amps. A couple resistors or a cap. Could even be a pinched wire touching the chassis. The power supply is shared by both channels so I don't think that is your problem. Anyway good luck.