On Tue, 16 Nov 2004 15:58:02 GMT, "Ian Iveson"
wroth:

The point I am labouring is that, if the valves are balanced like a
see-saw across a shared cathode resistor, then your symptom can be
caused in four opposite ways: either side can be pushed or pulled,
and the result appears the same. Combine this with an intermittent
fault and things get tricky. Without a circuit you could have an
intractable problem.

cheers, Ian


I would suspect coupling capacitors at either output tube grid since the
amp works until thoroughly warmed up. Cap leakage gets worse with increased
temperature. If the problem can be duplicated with the bottom cover off so that
voltages at the tube base can be checked, that would be a good place to start.
Screen voltage changes will also affect cathode currents. No schematics needed
for that.

If all else fails, a schematic can be "reverse engineered" by simple
inspection and a little work with pencil and paper.

Jim