"Off" vs. "Standby" and tube life

You'd better "Off"...

Don't ever live tubes on 24/7 or overnight. It realy doesn't matter if the tube will live longer or shorter it I guess matters to you more.

You can rely on circuit protection when the tube goes bad and you don't turn any tube component rightaway. If not you may set up your house on fire.

The safety issue is not limited to tubes. The tube itself won't start a fire, but the failure of the tube could casue other components to overheat and create a hazard. But, that is the case with solid state gear as well. Actual fires from component failure is not common, but I suppose there is some risk of leaving anything on all the time. Unfortunately, I do have to leave my refridgerator on all the time (but not, I suppose, the interior light).

From the Cary Audio website:

4. When is it best to turn my equipment off?

This brings us to an ongoing debate. Which is better-leaving the product on 24 hours a day or turning it on and off? Both will shorten the life of your tubes. So what should you do? The answer lies somewhere between the two. If you listen faithfully for several hours a day then leave the unit on. You do not want to turn it on and off several times a day. This is worse than leaving it on 24 hours a day. If you listen two or three times a week or just on weekends, turn the unit off when not in use. In this case, allow one hour for warm up time. For the weekend listener, turn the unit on Friday and turn it off Sunday night. This will optimize tube life for your amplifier. Preamplifiers and CD players should stay on all the time. The tube replacement cost for these units is considerably less than amplifiers. Most of our amplifiers have a Standby feature. The Standby is there to pre-warm the tubes before operating. Tubes generally last longer if they have only a few minutes of warm up time.

Most tubes will last for many years. Some will fail after a short period of time. As more tubes are being manufactured, the quality is excellent and the life is longer."

Larryi,

A refrigerator is less affected to fires than tube equipment.
Its life span is approximately 20 years and seing and also repairing older ones that, I've seen no fire damage.
Tube equipment has high voltages that could fry circuit board as a piece of paper. If you want me to show proof I can post photos of a PC board hole of an amplifier turned on 24/7 where just one EL34 tube went bad...
A similar "holes" I've seen when I repaired TVs but never I saw SS amp to have this kind of damage unless it's been used as a commercial DJ amp.

ANYTHING left on wears out. That is simple physics.