There are two issues: sound and reliability. I've found that most Class A amps running over 100 watts, need a LONG warm up time (like a day or two). Class A/B and B amps don't seem to need this kind of warm up (neither do low powered class A amps). These can generally warm up in an hour or two. I have found some amps that do not follow this so well. I have a Classe Seventy that sounds great after only 1 hour of warm up, but I understand the Classe DR series (small wattage) needed very long warm up times--they also ran very hot. So you need to determine what sonic improvements you get over the warm up time. The second issue is reliability. I listen to music a couple of hours a day. I don't want to cycle the boards through the heating cycles especially on HOT amps like Krell and Levinson every day (I leave them on for sound improvement as well--but even if that wasn't an issue I would still leave them on for reliability). The only time they are turned off is if I am out of town for any length of time. The amps I use for HT only get used about 2 or maybe 3 times a week, so I only turn those on when I'm going to watch a movie. I only let them warm up about 15 minutes--which is probably less than they really need, but it's for home theater and I really don't think I can tell the difference for that application.
Solid state power amps.; on or off?
Some people keep telling me that solid state gear should be left powered on all the time during day to day listening. They claim that thermal consistency will improve long term life and reliability. Power cost consideration appart, what is your opinion; experience?