Tube preamp, Leave On Always or ON/OFF?

Should I leave my TUBE preamp ON always or only turn it on when I am using it? Thanks
I'd turn it off. Wastes tube life. However, some tube preamps run the tubes at very low power, so that can litterally last a long time. Some questions to ask yourself, do you notice a difference in sound quality if left on for days at a time? Or after a hour or two, things are warmed up and sound fine? Are you running stock tubes that are cheap to replace? Or expensive NOS? Turning tubes on and off a lot can reduce life span.

What I do is on weekends, when I listen a lot, leave it on. During the week, goes on and off...
I substantially agree with Jfrech. Mine is a tradeoff. I use a very difficult to obtain tube with a 10,000 hours usable life. This is about a year and a half when always on. It takes my preamp about 2 hours to reach its peak, and I typically use it for 3 hours each night and about 5 hours each weekend. Thus I use about 41 hours per week turning it on and off, rather than 168 hours leaving it on. My tubes thus will last about 5 years.
If you have the dough to replace tubes often, then leave it ON; otherwise leave it OFF when not in use.
ALWAYS ON. Solid state or tube. Always.

I never turn mine off. It's an Audible Illusions M3A. It's known as a "tube eater". I had the same tubes in it (Amperex JAN) for 5 years. The JAN's are still good! I just took them out to listen to different tubes.

Think about it. Professional studios leave everything on constantly. Nothing heats up then cools down then heats up .... These expansions (heat) and contractions (cool) cause a shorter life.

To test this, leave a light bulb on. Isolate it from all vibrations. (You never thought you'd be using cones, cork, sorbothane, ... for that, did you?) That light bulb will last longer than any other light bulb from the same pack.
I used to leave them on all the time. Now I turn them off as I got tired of replacing them often.
Well, I'm glad to see this question was answered definitively. I understand the light bulb thing but I still can't see leaving tubes on 24/7 especially if they are NOS and you have paid big bucks for them.
I have a BAT VK-50SE and I like to turn it off when not in use.

The BAT has a soft start feature, which gradually increases the voltage to the tubes over a period of time (about a minute). It drastically reduces the stress on the tubes during power on. Turning this kind of equipment on and off should not shorten the tubes life.

The BAT runs very hot. The heat it generates may shorten the life span of other components inside. Leaving it on all the time is going to dry up the capacitors sooner.

Not to mention the extra electricity it consumes.

But if you have a preamp that has no soft start feature, drives tubes gently, does not run very hot, and uses long lasting tubes; than by all means, leave it on.
I leave everything on but the TT motor. It shuts itself off after 40 minutes, which is great on drinking nights! All the tube stuff has good NOS tubes. I hate waiting for everything to get up to speed.
The proprietor of one of the high end's more noteworthy and successful tube gear companies explained to me that the studies done in the 1950's on tube wear all confirmed that small signal tubes, such as those used then and now in preamps and now in DAC's, tend to last much longer (and as a corollary, also sound better) if powered up 24/7. Basically, he said that, if left powered up 24/7, they either die at some point in the first 250 hours (infant mortality of sorts) or they basically last forever.

I leave all of my equipment except turntable and tube amps powered up 24/7. Over the years, this has included a tubed DAC (Cal Audio) and three tube preamps (Jadis, CAT and Hovland). In fourteen years combined of these tube components being left on 24/7, I have never had to replace a tube (nine years now on the DAC), nor has any of my equipment, tube or solid-state, required service. The only precautionary measure I take is to keep the volume turned all the way down (and the mute engaged for other reasons) on preamps so as to ensure that there is little current passing through the tubes when I am not playing music.

Tube amps cannot be left powered up because the output tubes pass a relatively large amount of current that stresses the tubes.

As a general rule, it is the thermal cycles that occur when equipment is powered up and down (i.e., repeated expansion and contraction of the components as they heat up and cool down) that kills components, even tubes - it is basic physics.
Sidssp, I also have a BAT VK-50SE and put it in stand-by when I'm not using it. I only turn it off when I go away for more than a day. I'm surprised you turn it off rather than using the stand-by feature.

Good point, I could have done that. The problem is I have programmed a macro to turn everything on/off from a universal remote but the VK-50SE does not allow you to put it in stand-by from a remote. It can only be done by pushing the power button and I am too lazy or too forgetful to get up every time.
Raquel, that is interesting. You never replaced the tubes in your 3 preamps in 14 years despite leaving them on 24/7?

I'm going your route, and don't worry if I didn't get the same results. I'll just have to get those tubes replaced if their life span come to an end.
the VK-50SE does not allow you to put it in stand-by from a remote. It can only be done by pushing the power button

I hear you. Annoying, isn't it? At least it can be woken up from stand-by using the remote.

Long ago I had a Marantz 7 in which I had not replaced the tubes for over 5 years. When I did, I was shocked at the improvement. Tubes are deteriorating all the time.