You either got raised resistance of the cathode resistor(s) of the splitter,
low voltage to an element of the outputs or shorted something on the output.

Do you know how to use a scope in the DC mode ? Whatever the cathode voltage
is on the outputs, remember that and set the trace to a line somewhere, over
it. If the grid drive gets up near that level then the problem is after. Has
to be in the load or the bias of the output stage then.

If however you see that the output grid drive clips before getting near the
cathodes' DC level (of the outputs of course) then look to the splitter
stage. The way to tell if the cathode resistor value(s) has gone high is
that the plate voltage will be high. Usually.


** OTOH - the amp might just be hexed.

Don't you think ?



..... Phil