Leaving my amplifier on ok?

In general for tube amps it's better to turn them off. With one exception that I know. David Berning's amps. David designs for long life, very, very long life in total contrast to almost every other tube designer. I know from a friend who was there that David's first amp , the Audionics BA150, would last almost forever. The prototype was turned on in 1972 and turned off in 1977 and there was no measurable wear on the output tubes.

I can recall reading from more than one amp engineer designer talking about this subject. Yes caps are built better than in the past but they all agreed that the greatest factor to cap failure was not as much the excess heat as much as it was the constant hot cold cycle. Their claim makes sense to me as a hot cycle expands and a cold cycle contracts and this constant cycle of expanding and contraction is the cause of cracks forming that would lead to failure. Another is my real life experience with my sansui 7070 that I purchased in 1979. I moved this into my wife’s salon to run music in her business. Outside of power outages the unit has not been turned off for 30 years and it is still going strong with no issues. I will agree you do not want to leave tubes in biased mode as they have a defined life cycle. My current amps I never turn off.

Question was presented to a McIntosh tech some years back.

The response was a resounding NO. If it’s on its being used and any piece of equipment  being used does not have its life span increased by being used.

It is not so much heat/cold cycling that damages caps as it is the rapid inrush of current that deforms the cap.  But, any decent designs where this could be a problem would include a “soft-start” circuit that puts a high current resistor or a resistor that has high resistance when cold in series to reduce inrush current until the cap has been gradually charge to the point when a relay (usually timed) closes a circuit that allows full current flow.  Turn onTurn off cycling should not reduce component life (except for failure of the soft-start relay which is a common failure mode).  

I find that my Class A solid state mono blocks sound better after 96 hours. They run at body temperature. There are no electrolytic caps in the mono blocks to dry out. The power supply is in another room, where the electrolytic caps remain at room temperature. So I turn them off for heat domes, not otherwise.

Ain't DIY great?