In the sound coming from the left channel of my st70, there are noises which I can only describe as "beeping". It is not a hum or an oscillation.
When I move one or the other of left EL-34s, I can sometimes reproduce this beeping.
Is it an output tube, a socket or a poor solder connection going to a socket? Fairly recently, I did reflow the solder to every connection in the amp.
I could switch the right and left output tubes of the amp to rule out a bad tube, before "going into surgery" on the amp.
When the beeping first occurred, it ceased after the amp heated up. Now, it is does not cease to occur intermittently, despite a hot amp.
Could it be a connection going to ground temporarily or opening temporarily?