Keep mine on for about 15 to 30 minutes, prior to listening....its a tavish phono preamp with small tubes of the 12ax7/12au7/5751 variety. These tubes have a much longer life span than the larger power amp tubes. I will usually turn off preamp soon after listening, although I sometimes procrastinate and its left on for an extended period of time, not too worried.
rule of thumb: how long do you leave a tube preamp on versus turning it off then back on?
I just upgraded to an Audio Research REF 10 with 12 tubes and I am wondering how to best preserve the tubes. How long sitting turned on is equal to the wear and tear of turning it off then on again? I had a Rogue RP 7 with just four tubes so I didn't worry about this issue so much, I just turned it on when I began to listen then off at the end of the evening. Now I'm wondering where the sweet spot is? Away for a hour, two, three, turn it off when? Am I over-thinking this issue?