Warm-up time for amps and preamps

Atmasphere,  thank you for your post. That is how I understood it also. Heat is the enemy really. 

It is simply drying out of electrolyte.  Every 10 degrees Celsius temperature increase cuts capacitor life by half.  Presence of voltage on capacitor is beneficial since it is rebuilding dielectric layer (aluminum oxide).  Without voltage electrolyte slowly eats up this layer.

Well, maybe it's all in my head, instead of my ears, but it seems like my Kell FPB 400cx "comes in" after it's been on all day.  That's when I really think it sounds great.

My Gato Amp-150 has a "warm-up" feature that brings the amp to optimum temps in 15 minutes.  My other amps take about an hour or so.

My Accuphase E600 sounds fine after 20 - 30 minutes. Sure, it gets better after awhile but that could also be attributed to a second cocktail. I used to sweat this stuff but not anymore. I just sit back, off center, and listen to all of my music. Don't sweat the small stuff. As long as it sounds great after it warms up you're in better shape than all the people that can't part with money for room treatments.