Leaving tube amps on.

As jea48 says, most decent tube gear has a soft start circuit or if tube rectified, rely on the rectifier to gently bring the power up. It makes sense, from an equipment/tube preservation standpoint to turn off tube gear when not using it.  In particular, your MANY output tubes have a somewhat short lifespan when operating, and heat is not a friend for any of the other components in your gear (which is why their specification include lifetime estimations that are based on differing levels of heat).

As for sound quality, it does take some time for gear to warm up; the good news with tube gear is that it warms up much more quickly than solid state gear and will sound pretty good after a few minutes.

If I will not be listening for anything longer than 30 to 45 minutes, I will turn my gear off.

I would leave them on, assuming that I’m in close proximity to the amps and able to react quickly if a tube event occurred.

 I had an ARC amp that took 45 minutes to warm up and for the sound to bloom and I’ve had that experience with several of the amps I’ve owned. If you’re having short listening sessions, and that’s just the norm and unavoidable, you should be listening to your system delivering peak performance and not hearing the sound of an amp going through a warmup cycle. Your only offset (aside from safety) is that you’re going to be replacing tubes at a higher rate hence you need to decide whether you can justify the extra cost, or not. If not, buy some good solid state amps.

That would be my approach but I can also understand why some might disagree with it.

That is a great question. I got interested enough to read the manual and give it some thought.

My conclusion was simple. Call Audio Research and discuss with the technical representative (I forgot his name).

The new generation of ARC amps have slow startup and there is very very little improvement with warm up. You will have to assess yourself how much fidelity improvement there is as this is a bit older design. Also, that is a massive power amp… with 18 KT 150’s being run hard. So the recommended replacement time is 2,000 hours for those tubes. The small ones 4,000 hours. For me, balancing the above aspects I would turn it off if you were leaving it more than 15 - 30 minutes.

One thing I believe true however is that tube life is longer if left in idle mode with no music going through it… but then you will not be using the hours meter to change tubes at regular intervals, making maintenance more difficult. With ARC, I do what they say as far as tubes.

better safe than sorry. when tube goes bad anything can happen including anything that had been already happening.

leave tube amp on, you are at the fire hazard.