The only caveat I would add to leaving any electrical item on all the time is that you make sure you have some decent circuit breakers in the house in the event that anything serious does go awry.

That applies to refridgerators as much as to amps.[/QUOTE]

Now how would YOU do that? Fortunately, you don't have to. The National Electrical Code has already done that for you. And the electrician who wired your house and the town building inspector are also on the hook.

Having a car warm up and having an amplifier warm up are entirely different things. With a car, you are circulating oil to lubricate mechanically moving parts that have friction. You are also warming hydraulic fluid that operates your transmission and steering. There are also critical mechanical tolerances which change when temperature changes. When vacuum tubes warm up, their "thermionic emission" characteristics change. That's one reason why we use feedback in tube circuits. When bipolar transistors warm up, they change too. And if they are not thermally stabalized, they can go into what is called "thermal runaway." And then they are dead.