How do I break in a tube amplifier?

Note that it's OK to leave it unattended when it's not on. Waiting 3 hours to turn it on after turning it off is silly. Tube amps, if designed and built properly, are tough little buggers and don't need nearly as much pampering as many think. My experience says you should simply enjoy the damn thing and it will "break in" from listening to it, and might last longer than you with less upkeep.

Did Audio Research tell you where you should wait? Can you pace around or should you just sit there? Leaving a new tube amp on for one hundred hours continuously is fine if you're going to sit next to it...this should be easy if you have 2 kids as they can visit you from time to time to see if "the insane dad" is still breathing. The "bloom plateau" is often only a power surge, radiation leak, or stomach virus, group hallucination included, but your results can vary. There is no "3 hour wait" rule by the way, so feel free to ignore that one, and anything I or any of the other certified nut jobs around here say.

I do think it's important to turn it on before listening to it, although leaving it off all the time does make the tubes last longer.

Take the tape outs...cleaner.

Tape outs generally bypass the volume pot of a receiver, although I'm not sure about the rest of the circuitry like tone controls and all that...they're designed that way due to the fact that tape decks have input faders that should be impervious to preamp gain.

Preamp outs would be better if available.

No...do not play the amp until you've rested your ears for at least 112 minutes, you've cleaned up around the amp to avoid the dreaded "dust particle comb filtering", and you're made sure all the neighbors have shut down any major appliances. Then you're all set.

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.