What would be normal and what acceptable for a solid state or valve/tube
stage amp. ?
Well you would not want the gain/ output audio to go up over an hour of use
with a constant input.
Testing a solid state amp that had a problem that certainly affected the FET
gain killer protection circuit so (falsely) cutting the output over an hour
to close to zero. But checking to see if there was any other gain drop
problem but then realised I don't know what the norm is.
Amp rated at 200W (music power) which I've taken as 100W (continuous RMS if
you could). Running a constant source of 1Kz through amp to give a
continuous 1/5, 20W in a dummy load , which with heating itself is not
necessarily constant. Result of testing over 40 minutes was a 9 percent drop
in V rms into the load so about 20 percent drop in equivalent audio watts.
No fans on this amp and the heatsink settled at 68 degrees C after about 30
minutes. The output was still dropping after 30 minutes but very much slower
and decided to cancel after 40 minutes

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/