04-17-2017, 06:47 PM
Is it possible the tube is gassy, are these the new ones or the used ones? Did you measure what the bias voltage on the grid of each output tube is? As for the coupling caps I agree with the others and would just change them to be safe. Just Radio has those JBX caps which are cheap, seem to sound just fine and best of all are black. They don't have the cheap yellow cap look when installed.
Gregb
Gregb