Gents.... A follow up to this thread with a question about tube sockets.
My friend has been using this amp during the last year. He had someone else swap out the rectifier and output tubes. The amp is plenty loud - EXCEPT that is drops in volume for short spurts then goes back up to full power. That is the problem - it is a quick drop in volume then back to full power. So it is hard to get voltage measurements or to see this on the scope. I'll try to use a sine wave to see if this will happen again and if I can see it on the scope.
I noticed this problem with BOTH channels.
My initial testing included -
(1) Swap out the Rectifier tube - No difference
(2) Swap out the 6V6 Power tubes - No difference.
The tubes mentioned above are tight in their sockets and no visible corrosion.
So... knowing that this happens going through both channels, that leads me to the Phase Inverter and beyond.
I noticed that all the 9 pin preamp tubes are very loose, including the Phase Inverter. So I want to swap out these sockets. I tried to retension the sockets but I think they are beyond help. I see that Antique Radio Supply sells shield base tube sockets - some have the Center Shield, others do not. I don't know if there is an advantage to having the center shield. Anyway, this is something that needs to be done and at least I will be able to rule out a loose tube connection.
After that, if the problem continues, I'll dive into the right side of the circuit.