How do I break in a tube amplifier?

I don't monitor the warmup of my tube amp because it's generally on providing background music from the moment I start my day until I can get around to doing some "active listening." I can comment of guitar tube amps though, because when I plug in to practice or record or simply try to entertain my neighbors, It really settles in after 20 minutes to a half hour or so...this with any one of a number of tube amps I currently use, and especially with a Class A amp I just bought. So there.

My tube amplifier is in a cabinet that I either leave the door open on or just remove when the amp is running. I have noticed that if I turn the amp on and leave the door shut for a few minutes it really warms up much faster.

Is this a good way to speed up the warm up process? Obviously, I don't plan to leave the door closed for a long period of time, but it seems that 5 or 10 minutes could really speed up the process of getting the amplifier closer to fully warm operating condition.

Is heating up faster significantly harder on the tubes themselves?

I just upgraded my Cary 300SEI. All the upgrades will take 300 hours to break in, partly due to the Duelund Silver Bypass Capacitors. For the first 150 hours, I’m running it 15 hours a day using my tuner and cheap headphones. I’m using cheap tubes for this part of the break-in. I’m not comfortable leaving it on while I’m sleeping.

For the next 150 hours, I’ll put in my good tubes and use my good headphones to just enjoy the music, mostly through my CD player. And I’ll run the burn-in track on my IsoTek Full System Enhancer CD an hour each day. I’ll use the cheap headphones during this time. The IsoTek CD really helps in speeding up the break-in process. I use the 5 minute demagnetization track one a week and it makes a very audible improvement. https://isoteksystems.com/products/full-system-enhancer/

I think you should just use the amp as you would normally do and let it break in on its own.  It is not like it will sound horrible in the process, it just may, perhaps, not b at its best.

My tube gear sounds quite decent after five to ten minutes of warm up.  Tube gear gets up to song much faster than solid state stuff after being turned on, but, the downside is that it cannot be left on all of the time like most solid state gear. 

It does NOT make sense to leave tube gear on for extended periods when you are not listening to the system.  Tube life is limited by the hours of the gear being on.  Tubes are NOT like incandescent lightbulbs and do not suffer, to the same extent, from the thermal shock of being turned on (particularly if the amp uses tube rectification and/or soft-start circuitry).  But, once you turn a tube amp off, wait at least a few minutes before turning it back on; some amps don't like being short-cycled and may make loud noises if short-cycled.

Of course the particular gear matters, but, in my setup, I have not had ANY kind of service issue, including tubes going bad, in well over ten years of operation of my current gear (tube linestage, tube amp and tube phono preamp); the same cannot be said of my music server.

Never leave tube amp on all the time very bad idea.