With no input, and power applied, both channels ping their meters, and there is a loud hum from the transformer. When I say ping the meters - the meters go full scale and back to zero or 1/2 and back up, and so on and so on. Looks like oscillation.
Is there something obvious to check or will this take a major effort to fix? service manual anywhere? I am an ex- EE and can probe everything, can bring it up with a variac, can take some oscilloscope screens if you would like.
I tried it with inputs grounded, same thing as with open circ.
I then tried it with a signal on the inputs at very very low volume, same result.
all this with no load on speaker terminals.