thanks, fellas. My next step was to use the TT as a source and see what happens. But to do that, I have to put the EAR back in the circuit for the phono section. Worth a shot.
One riddle- why, if it was the Ayon, would one channel go silent with the MastersounD and the opposite channel buzz with the Frankensteins?
Wouldn't they both buzz or go silent?
I'm also wondering if the power supply up here is incredibly dirty. Not only do we get frequent surges with flickering lights, but there's a slight buzz coming from the Monster surge protector unit I use. Now, neither the amplifiers or the EAR is plugged into the Monster unit. The Franks and the EAR run through a BPT line conditioner, which runs into the wall. The Ayon runs through the Monster unit. The MastersounD runs right through a wall outlet.
If something is wrong with the MastersounD, at least I know it's not the pre-tubes, since the same channel cuts out using it as an integrated or as a direct power amp.
Might just replace all the signal tubes on all the amps if the TT trick fails.
This is the one drawback about an all tube system- lots of variables in trying to pinpoint a problem.