I have a JVM215C and the other day I was experiencing some issues. I thought it might be power tube related so I re-seated the power tubes but that did not help and the amp was still making a high-pitched squeal. The squeal would come and go but other last 3 days, it was pretty consistanct. I also noticed that the amp at times would go from a muddy-low powered sound to a more clean, high powered sound. I then removed the head from the combo so I could test the bias of the tubes. For one side, I get 33 but for the other, it will not register. The amp has not made the squealing sound today so I wondering if maybe the tube for that one socket is dead (although it appears to have power to it -- and its not white). Can someone let me know if a faulty power tube could make one side of the bias terminals not register?
thanks!
joe...