temp on power tube plates?

[istvan01]

I have all DHT monoblocks with SE-PX25M/PP-2A3M/PP-520B Plitron OPT on end. The tubes have been working since 2005 great.
I have a radiation thermometer and this can measure through the glass temperature of anode plates. The plates have highest temp on top.
I measured 188-195C on 520B /115mA-470V/
102-107C on 2A3M /45mA-225V/
70-72C on PX25M /24mA-240V/
My question is, what would be minimum and maximum operating temp of these tube plates?
Does exist optimal temperature on plates, according to life time also?

[MaciekP]

Really can see through glass?

https://www.thermoworks.com/infrared_th ... f_infrared

"Do not "see through" glass, liquids or other transparent surfaces - even though visible light (like a laser) passes through them (i.e. if you point an IR gun at a window, you'll be measuring the temperature of the window pane, not the outside temp)"

Talking about bulb temperature, for some tubes I saw the max of 250C.
For many transmitting tubes it is allowed to have red anodes and it is fine.
I'm sure JAC can share his experience on that...

[istvan01]

Really can see through glass?

https://physics.stackexchange.com/quest ... e-of-glass