Best temperature for optimum tube performance

Thank you one and all for weighing in...
As an aside, I drilled a series of 1-1/4” holes in the upper back of the cabinet to provide convection venting....the two independent top drawers hide those holes.
I did install a small, quiet computer fan but it just couldn’t pull enough air to keep the gear from cooking.
(I was petrified to see millercarbon had replied.... I remain yet unskewered...love to witness the dust-ups he provokes.)
The temp gun is a great idea....

I use one of their component fans with front exhaust on my Parasound 5 channel SS amp. They have other fans for cabinets.

https://www.acinfinity.com/quiet-cabinet-fans/

Wow, those fan solutions are very inexpensive. Imagine if they were sold by Synergistic et al?

I can only add this... I have an Audio Research D160 tube amp from the early eighties, 1982 to be exact. It uses 6550 tubes biased to 65 mV, according to factory specs. Way to hot for any practical life. I have "detuned" them to 46-48 mV to calm things down while maintaining proper gain.  The amp came equipped with two fans to bathe the tubes in cool air.  And naturally, per the owner's manual, the amp takes a couple hours of use to achieve thermal equalibrium. Use this to your benefit. The detuning and the fans really help in this specific example.

Happy listening

Fall, Winter, Spring, CHANGE! That's me. I can't take the heat, and I can't take the noise from the fans or AC in the Summer.. I change amp types, plane and simple. Class D are just fine with a little tweak here and there for the 3-4 months of heat.. 

I look over the valve amps, make any changes I want to do.. Then they go back in service around Halloween. If we have a party here, after the party.. :-)

Sometimes I sneak out my MC240 or 225 in the summer, play the Beach Boys, on the deck. Pair of old Heresy's or something. It just works.  

Regards