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

I have noticed the same thing with my tube amps, both my flea-powered 46 SE amps and my 50W PP amps. After 2 hours or so, I can hear greater detail and the soundstage has more of a see-through transparency. It's not a night-and-day kind of thing, but the music consistently sounds better a couple hours into a listening session.

I don't know any technical reason for this but it may have something to do with the heating of the transformer cores. A year or two ago I replaced the power transformers in my 46 amps with tranformers rated for higher current, and I notice the "warm up" differences much more now than I did with the old transformers.

Any real good system needs to warm up for an hour or two before sounding best. I deal with it by playing digital...then I switch to analog.

Are you saying let em warm without playing any music helps your tubes sound better or???