Threshold 400A Amplifier and Conrad Jonson MF2500A

The 400A is a Class A amp, so yeah, it runs hot and should.

I have a pair of Class A mono amps that run really hot and sound better the hotter they get.  

IMHO, you should always leave Class A amps on 24/7.  That provides the thermal stabilization that they require to work and sound best. Only turn them off, if you're going to be gone for an extended period of time.

I've owned several different Class A amps and they have all behaved the best when left on all the time.  My favorite amps are Class A, just a personal preference, but they sound the best to me.

Thanks for your advice, I will leave it on all the time. So the temperature does not affect  the live span of internal parts?  

There are two sides to that question. IMHO turning it on and off is worse than leaving it on all the time, but some others will argue with that.  The in-rush of current, stresses the internal components when the piece of gear is turned on and off, (unless the equipment has a "slow start" circuit).

Class A amps do run hot and depending on where you live and the season, they can sometimes force you out of the room. Also, if electricity is expensive where you live, that’s another concern.

Over my many years in the audio biz, I’ve found that leaving SOLID STATE gear on all the time, stabilizes and reduces wear and tear and makes them last longer.

With tube gear, I always turn it off to keep from replacing tubes so often, which can be expensive depending on the type of tube.

Maybe Al, (Almarg) will chime in on this subject. He’s our resident electrical expert and I’m sure has stated a few times his feelings, but I can’t find any of his comments about this subject right now.

YMMV...