Should Class A Amps be left on??

No do not leave them on all the time. The heat generated will lead to pre mature failer.I have owned several Class A biased amps and they need about an hour of warm up to sound good.Also youd be wasting electricity.

Does "standby" count as being on? I've left mine in standby mostly since I did not want to run the internal fans continuously. I figure that these would be the first bits to go. Any thoughts?

Well, I have tried leaving my Aleph 5 on for extended periods after all of this discussion and I must add that...

It is incredible how removed the amp becomes and music forward after one, two and even three days of power on. I am now sold on not turning off the amp overnight and only turning off for longer than 36 hour periods.

Other than the power bill the only downside I have come to experience is the desire for more dynamics that micro fade after extended power up periods.

In a word how does the Class A Aleph 5 perform after extended periods of power up, Incredible!

Sayas: Thanks for the follow-up. Hopefully, your posting of honest findings based on first hand experience will encourage others to check things out for themselves. It is good to see that, even though you initially thought your system sounded quite good, it sounds even better now. As you've found, it sometimes pays to have an open mind and experiment : )

As to the slight fading of dynamics that you are experiencing, i have to wonder if your amp is receiving adequate aiflow. It sounds as if the amp is running TOO hot, which can make them sound dynamically constricted in my experience. How much open space do you have on top of and around the amp ? I know that the Aleph's are all heat-sink, but anything that you can do to let the heat naturally dissipate through convection will only help the matter. Sean
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Sean, the 5 is in a basement on concrete, underpad & carpet and marble slab with nothing surrounding it for 4'. Airflow, cool air is as good as it gets. The listening room is 70F or cooler.
I am confident that the convection factor is as good as I can make it.