I keep my stereo stuff on, 24/7/365. Though I do turn off the amplifier some of the time when not in use. (Lately I am back to also leaving the Bryston 4B-SST2 on all the time also)
On another site someone was adamant about leaving stuff on was very bad. So i Googled: "Mean time to failure" or the like, and found particular comments that made it clear: (paraphrase) The PRIMARY cause of failure is cycling. (which is the on/off/on/off as number one cause once the first 'faulty part' failure phase has passed .. the break in phase)
((Added: so it reasons one SHOULD turn electronics on and off a LOT during the first few months of new ownership if the warranty is of short duration, to stress parts that will fail. So they fail during the warranty!!))
So leaving stuff on is going to make it last longer. Not shorter. And since the notions about caps etc are all theoretical gossip.. i would put my bet on the tested, and thus the primary cause of failure is the repeated turning an electrical product on and off. (solid state and electronic circuits, tubes are mainly just the tube life, they would last more hours left on, but the usual time off is way more than the life added, so they would seem to last a lot longer if turned off.)
Over the years i have to say stuff sounds better after at least a half hour, and even better 24 hours left on. It is not a lot, mostly better air around the instruments.. But at the level of audiophilia I'm at, that air would cost $10,000. to $30,000. MORE to have at turn on..
I would not leave tube amplifiers on, unattended! (Tube preamps are OK, if you are willing to have a shorter tube life).
A tube amp could have a catastrophic tube failure. Not likely, but stories of power tube pyrotechnics/fires make it not safe to leave a tube amp unattended for any length of time, (unless you a prepared for a fire, like have your tube amp sitting in a large sand-filled concrete bunker...)
Brown outs would really only be dangerous if the stuff was playing as far as I know. If it is idling, I don't think the stress would be enough to be dangerous for the usual circuits. (I have heard there is some type of power supply circiuts which could be damaged?)
Anyway, Since I use power conditioners, they have protections for major power faults.
And since i am now retired, and play music at least 10 or more hours a day, every day... i might as well leave it all on.
