How should you treat your tubes?

For a stretch of an hour or two, I would not turn off either, certainly not the preamp anyway.

Beyond that kind of time, a lot of different considerations come into play. Not only is the life of the tube at issue. Heat can damage other components, so leaving on tube gear, particularly if the tubes are enclosed or if you are dealing with hot output tubes, can result in shorter life for such components.

Other considerations include whether the equipment has "soft start" circuits (slowly brings up circuits so thermal stress on tube filaments are reduced) or if the power supply employs tube rectification (also results in slow turn on). With such slower turn on, the issue of wear from the turn on part of the cycle is reduced.

Probably the best answer would be that provided by the manufacturer.

Small signal tubes such as 12AX7's or 6922's are generally best left on 24/7. Quoting from the "TIPS & ADVICE" section of the owner's manual to my VAC Rennaisance 140/140 Mk. III tube amps:

"How long should tubes last? It has long been known in professional circles (and probably now forgotten) that a tube such as the 12AX7 will display BETTER performance characteristics after TWO YEARS of CONTINUAL operation than when it was new. In normal use it is not unusual for a low level tube to last 5 years or longer. Output tubes [i.e., power tubes used in tube power amps] are another story, as they are continuously providing significant amounts of current." (Emphasis original).

The expansion and contraction that small signal tubes undergo as gear heats up and cools down (as a result of being turned on and off) takes a toll over time. In addition, the voltage rush at turn-on is especially hard on small signal tubes. Tube gear with tube rectification is a lot easier on tubes at start-up, and some tube gear has a soft-start feature to soften the blow, while solid-state rectification is hard on them. In summary, while it is to a certain extent model-dependent, it's generally better, for both tube life and for sound quality, to leave tube preamps (and other gear that uses small signal tubes, like DAC's and tuners) on 24/7.

After a few years, the tubes should be replaced, as they do start to "lose their luster" (see Kevin Deal comments above), but they won't fail if used this way -- generally speaking, tubes left on 24/7 either fail within the first 250 hours or so from "infant mortality" or they last forever.

Output tubes cannot be left on 24/7 because they pass a lot of current and will wear out relatively quickly (not to mention wasting a lot of electricity and occasionally dying in spectacular fashion -- best not to leave them unattended).

Raquel,

That is interesting information from a manufacturer. But, how would one keep the small tubes (input, driver, phase splitter) of a power amp, like the VAC 140/140, on while the output tubes are not on? Does it have some sort of standby feature?

Also, while it is generally true that linestages have small signal tubes that don't degrade very rapidly under constant on conditions, that is not always the case. For example, the Counterpoint SA 3000 is pretty hard on tubes.

I might also be a bit leery about leaving on a linestage that had a lot of expensive small signal tubes in them (fortunately for me, my linestage uses cheap 12B4s for signal tubes). Still, I turn it off when not I am out for a long period of time. My phono stage has Telefunken ECC83s in it and uses two 300b tubes as rectifiers, I really hate to leave it on when not in use.

I had a thorough response written and I lost my Internet connection and my text.

Larryi: The VAC 140's have no means of powering up only the 6SN7's. The amp is either on or off, and I turn it off and on as needed. The 6SN7's are not a worry, however, as they are exceedingly hardy tubes that were primarily designed for use in televisions -- it is not unusual to get 40,000 hours out of a 6SN7. The comment in my owner's manual was about small signal tubes generally. Kevin Hayes of VAC is also quick to point out that the studies done in the 1950's established that small signal tubes last much longer and sound better if left on 24/7.

I might be reluctant to leave a tube preamp on that has a lot of tubes in the power supply (or that uses pentodes in the power supply like the ARC Ref 3 or big Jadis two-chassis or a really pricey tube like the 300B). I would be MORE inclined to leave a preamp having expensive NOS tubes in it powered up 24/7 precisely because such use tends to increase tube life.

For the record, I owned Jadis, CAT and Hovland tube preamps, and still have a CAL Audio Labs tubed DAC in the closet that I've owned since 1994. In a combined nine years of running those preamps 24/7, and another six years of running the DAC 24/7, I never lost a tube (the DAC sounded better than ever the last time I had it in the system) and only retubed the preamps when I sold them so that the new owners would have a component with brand-new tubes.