I have an old Model 5. If I'm going to be off from work for a couple of days, I leave the amp on 24/7. It sounds OK after being on for 1-2 hours but sounds way better after being powered up for 1-2 days. Besides, in winter here in the Great White North, it's a nice space heater.
I also have a Capri preamp that stays on at all times.
I also have a Capri preamp that stays on at all times.