Seems like the best "upgrade" for tube amps....

That's good to hear about KT-120s. I have been using my pair for over a year so maybe I have a few more years to go. Mine are run pretty conservatively----500v and 65ma---so that should help.

By the way, I don't see any point in waiting very long before playing music through the amps. I usually let mine warm up a couple minutes (while I am sorting through LPs) but that's it.

Interestingly, a few hours of warm up applies to solid state gear as well. In fact the manufacturer of my solid state preamp recommends at least two days of warm up before listening, then leave it on continuously, turn it off and you will start over! I believe that these warm up periods involve the electrons finding their shortest signal path as well as transistors or tubes reaching their optimum temperature.

Jolida 502p, and I run it a lot.

With solid state gear if you want it to really sound right it probably has to be left on all the time- especially preamps.

Our amps seem to get to 99% of where they are going in about an hour- two hours they are totally there. In the old days it took more like three. I credit component improvements for the shorter time these days.

I have a Van Alstine Synergy 450 which has 12 separate power supplies,
Frank made the statement there were at their best within 10 minutes.
I was dubious but he was correct.