Is it a OK to leave tube pre-amps powede up 24/7

There are only so many electrons in a vacuum tube.

There might be a limit to how many electrons can **flow** through a vacuum tube... I've seen some 6SN7s go over 50,000 hours in our gear.  Admittedly, that's an outsider number but some tubes have very long lives!

I'm much happier this way, but am I doing it any harm?

No.

Thanks for the reply

Don’t have much to add here, as about everything has been said!

For me, I turn off all of my tube gear (4 power amps and 3 preamps) when I don’t plan to listen to it within the next 2 hours. To my ears, all of my tube gear sounds great within 10-15 minutes of powering on. Some say an hour, I just don’t hear any difference of 15 minutes of warm up vs 60 minutes. The temps inside the tubes are pretty warm within 15 minutes.

I do know a guy who runs his preamps 24x7 and has for about 10 years now. Over 150,000 hours on his tubes and they still test as very good. I also know people with tube preamps from the 60s which still have their original tube sets in them - not run night & day for 50 years, but used a lot along the way - and powered on and off thousands of times. Some tubes do have very long lives!

Personally, I've never had a preamp tube burn out so I don't know how long they last.

I've notice even if I leave my pre-amp on all day, it takes about 30 minutes of playing music (especially the phono side) before it really kicks in.
I see no point  in leaving it on all day now

After looking over this entire thread, it appears that the approach to this conundrum varies based on the preamp you have.  Different circuit topologies must be kinder or less kind to the tubes when left on 24/7. Vive la difference!