Brian,
I tried switching tube, IC's, speaker wire, to no avail. There don't seem to be any loose connections on the amp terminals, plus I had not touched the amp since last night, when it was working fine. There must be something broken in the circuit that lets enough power go the the input/output tubes, but broke the audio connection. Either way I guess I'm going to have to take the board out of the chasis, which means unsolderinga good dozen wires.
Braden