How should you treat your tubes?

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).

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.

A final point: if you search the threads, you'll see that this subject has truly been beaten to death, as well as the more general subject of whether to turn equipment on and off or leave it on 24/7. In those threads, you'll see that repair techs and equipment manufacturers who contribute comments pretty much unanimously advocate leaving all equipment other than tube amps on 24/7 in the interests of longer component life and better sound. If you see the contrary in your owner's manual, it's for liability reasons -- the one component in a million that catches fire is going to result in a lawsuit for the manufacturer, so owner's manuals generally say "turn it off while not in use".

In response to one of the above posters, this is actually a case where the rejection of common sense and reliance upon the basic laws of physics is the way to go -- all matter, whether it is the concrete pavement of a freeway or a vacuum tube or silicon transistor in hi-fi gear, expands as it heats up and contracts as it cools down, and it is repeated expansion and contraction that compromises the physical integrity of these things over time. Keeping gear powered up keeps it at a relatively constant temperature, whereby there is little expansion and contraction -- the only downside in terms of component wear is that it can shorten cap life (capacitors are constantly being beaten by the oscillating 50 or 60 volt cycles of the electrical supply).

It is especially important to leave solid-state power amps and DAC's powered up 24/7. Naim, for example, says that it takes two days for some its amps to reach optimal operating condition (one of my dealers says "Naim amps need a week"). DAC's tend to sound like utter shit without lengthy warm-up (count on 24+ hours for most) and MUST be left on 24/7. I would add one exception to the solid-state amp rule -- Class A biased solid-state amps (e.g., Plinius or Gryphon) burn a hell of a lot of electricity and will turn the average room into a sauna if left on for long periods of time, and should be turned off when not in use as a result.

Of course you want to unplug hi-fi gear when there is an electrical storm or if you go out of town for two weeks, but for day-to-day, leave it on if you don't want it to break and if you want it to sound like the manufacturer intended.

EL-34's are used as output tubes in guitar amps and tube amps, and are also commonly used in tube power supplies. As I noted above, tube amps should not be left powered up, if only because output tube failures can be speactacular (I've made a mad dash or two myself -- nothing like that arcing and/or cracking, and the tremendous noise coming from the affected speaker).

"For longevity it's got to be leaving it on BUT what if the difference was 10 years for on/off or 20 years always on? Do you really think you're going to keep it for 10 or even 20 years?"

... I respectfully beg to differ from the right honorable contributor and friend Tbg. New-ish hi-fi gear actually breaks all the time and my crusade to get the truth out about this issue is explained mostly by my desire to avoid buying a used product that has been misused through repeatedly being turned on and off, and which is thus much more likely to break in my hands, causing me expense and aggravation.

Don't get me started about other misnomers in this hobby. Ads for gear being sold by the "original owner" that has "only been used thirty hours"??? This means that the seller is either a liar (and, therefore, God knows what he's selling) or an ignoramus (and I'm going to have to run the virgin in question for hundreds of hours with a break-in track before it sounds right). Like I said, don't get me started ... but I WILL say things about:

... People selling preamps and phono stages that their ads display sitting on top of subwoofers.

... "This product is an original Mk. IV, not an upgrade" -- as long as the upgrade has been broken in, totally irrelevant.

... "Reviewed favorably by HP in last month's Absolute Sound" -- every single component or speaker that windbag reviews is the next great step forward in the advancement of reproduced sound (excuse me, I meant the advancement of "continuousness"). For that matter, aside from Cordesman, when was the last time that magazine published a review that contained some real substance and that was not incredibly flattering? The difference between TAS and Stereophile has become striking (Stereophile reviews being much more detailed and, of course, featuring extensive measurements). In my opinion, TAS has become a sham and I've stopped subscribing.