After warming up the amp, I used the camera to measure the envelope temperature of the big KT88 valves.
Not surprised at the 172º reading. (340ºF)
Strangely this one runs a little cooler than the rest. Its bias current is the same, 50mA
From the KT88 Datasheet:
The question you may be asking: what was playing through the amplifier during this photo session? Glad you asked. Icehouse... Man of Colours. Since I'm going to be seeing them live tomorrow.