My best troubleshooting tool for tube amps with intermittent issues affected by shock or temperature has been my plastic chop sticks. I go around tapping on or around all components and see if anything changes. Something I learned from Mr Kendrick and found it to be very useful. I am also an...
I let the amp warm up for several minutes and after playing for a little while the amp suddenly goes very loud, then normal (?) then loud again, normal ......
I have not done much with it but noticed the bias voltages do not regulate well. I noticed it drifting any where from 71 to 78 mv...