"N_Cook" wrote in message ...

As though a thermal protect measure is cutting in falsely, but all valve.
10 minutes at gig level, longer at practise level, initially looses bass
and then over a couple of minutes vol drops to uselessly low.
Switch off ,cool down, and fine again.
I'll check with a variac, to simulate gradual loss of DC, but is that
the symptom sequence of loss of DC to a valve amp, lose bass then lose vol.
Valves have been swapped out , but not the rectifier bottle, likely
suspect?, a saggy 2x4007 lump will go in there initially to check that.
A hot-air gun looks a promising tool.
No hum reported, unlikely a major cap problem,a minor cap problem,
surely not a Tx problem







You could check it is not a dry jointed heater connection to one or more
valves.


Gareth.