When to Poweroff amps and preamps

Mine are all SS, i leave them on 24/7-the amp in stand by. If i leave over night  i unplug from wall.

heavy - is your MC240 stock ? Mine is 1961 and super modified.... sweet amp for sure.

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All 5, MC225,2x240s,275, and a pair of 60s are all stock, I have all the parts for PS, upgrades and pio caps, and a pair of 24k cases for the 60s.
The one 240 though has EU caps in it, so they didn't self destruct, like a lot of the other bumblebees. It is VERY special, indeed.
 I did mod up a 275 GG, that I managed to blow up a while back, (cable drop), it's quite a bit better than stock. Still it's a KT88 unit.. Not my favorite valve. I'm a 6550, El34, 6L6,  guy these days.. :-)

Summer/Winter, wahoo, night and day where I live. 33-35 is considered cold here, and it is, if you get caught in it. But I've seen, 45 at night, and 105 in the day, two days apart. Tube gear is not real partial to a REAL cold starts. My Cary stuff can pop a fuse with a real cold start too.

Regards

My metronome C6 preamp (with tubes) is always on “stand-by” when I don’t play. The Wavac 805: after listening:”off”. To put on your equipment: first Source, than préamp, than Poweramp. For turning off: first poweramp,than preamp an at last: the source.

I have two systems and leave the PS Audio PowerPlants on for both. But I power off my tube integrated when not in use. I leave on my Pass Labs preamp. But everything else that is SS and can go on standby mode I put in standby mode. On my headphone station I power off all the gear that I can reasonably power off. Most of that is SS. One amp is a Schiit Moljnir and I power that off. 

Always off, unplugged from power.
 When I will listen, I will power on amps, pre and disc player 24 hours before I listen.
 All solid state gear.  
 Goes for both my systems, they sit dormant and unplugged until I want to have a listening couch sit down.  
I may go months without listening, and when storms roll in, they are already unplugged.  Vacations, when not in use, they are unplugged and not in use.

as mentioned,  if listening on a fri & sat night, I will power all on, and leave on for the whole day and afternoon starting on Thursday, to allow them to warm up.

  Amps on first and off last has never failed me!

  They always sound better after a good 24hrs+ of being powered on and sitting idle!
 Been doing this since I was a wee mite in 1985 with my first separates system!
always took care of my gear, as I payed for it w my own money!
You may do whatever you feel is right, and works for you.