Preamp Eats tubes..

Assuming the preamp is not malfunctionning, you almost certainly won't have a problem if you keep your preamp powered up 24/7. It is dead wrong that running small signal tubes 24/7 shortens life -- the studies done in the 1950's proved the exact opposite. With few exceptions, such tubes last basically forever if they get past the infant mortality stage (+/- 250 hours) and are left on constantly. Counter-intuitive, yes, but true -- just like transistors, it is thermal cycles (i.e., turning things on and off) that kills electronic components. Many tube preamps also do not ramp up power to the filaments at turn-on, the tubes getting kicked in the groin when the power hits them.

Output tubes have to be turned off when not in use because they pass a lot of current and thus wear out relatively quickly.

Raquel,

on quite a few preamps the preamp tube are peak-driven like a power tubes and so the life of them will shorten significantly when left on 24/7.

in power amplifiers the bypass electrolytic caps can wear out faster than tubes turned on 24/7 thus resulting very often overbias and dead tube thereafter.

Marakanetz:

The preamps to which you refer are relatively rare. I would qualify what I wrote by pointing out that preamps using tube-regulated power supplies cannot be left on 24/7, as the tubes in the power supply are relatively stressed.

Tube amps are not the issue -- they can't be left on.