Do you leave CD players with tube outputs on?

You have it correct. I would suggest leave it on during a day you are going to or are listening to music and turn it off at night to preserve tube life. If the electronic caps and such are already broken-in in the player then I don't see them requiring much time to reach their full potential.

I am not sure of the technical aspects but I turn mine off when not in use . It only takes about one CD's worth of play to bring it in to its own and sound good .
Living in the lightening capitol of the world makes it dangerous to leave these things on when not in use ! I have already lost a heatpump and microwave oven .

Happy tunes .

Here we go again (these questions come up constantly). Your post and the responses demonstrate a misunderstanding of small-signal tubes (i.e., 12XA7's, 6SN7's, etc. found in tube preamps and tubed DAC's/CD players). In fact, 24/7 operation EXTENDS the life of small-signal tubes in most preamp and DAC circuits. Consider the following 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 [small-signal] 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).

Small-signal tubes pass little current in most preamp and DAC circuits, and thus experience virtually no filament wear. If left on 24/7, they either die within the first 250 hours or so due to "infant mortality" or they basically last forever. What kills small-signal tubes is two things: one, the thermal cycles that result from turning equipment on and off, and two, the voltage rush they see at power on. This occurs if they are in a component with solid-state rectification (i.e., solid-state power supplies), which is almost always the case. The rare component with tube rectification can be a different matter because the tube power supply functions like a variac to apply current gradually (for the same reason, many tube components have "soft start" circuits so as not to decapitate the tubes at power on). This, not 24/7 operation and heat, is the main culprit of tube death. The Colossus computers used in World War II to decipher enemy radio transmissions used thousands of small-signal tubes. The Wikipedia entry for "vacuum tube" has this to say about operation of the Colossus:

"The Colossus computer's designer, Dr Tommy Flowers, had a theory that most of the unreliability was caused during power down and (mainly) power up. Once Colossus was built and installed, it was switched on and left switched on running from dual redundant diesel generators (the wartime mains supply being considered too unreliable). The only time it was switched off was for conversion to the Colossus Mk2 and the addition of another 500 or so tubes. Another 9 Colossus Mk2s were built, and all 10 machines ran with a surprising degree of reliability. The 10 Colossi consumed 15 kilowatts of power each, 24 hours a day, 365 days a year—nearly all of it for the tube heaters."

The Wikipedia entry for the Colossus emphasizes this point:

"Colossus used state-of-the-art vacuum tubes (thermionic valves), thyratrons and photomultipliers to optically read a paper tape and then applied a programmable logical function to every character, counting how often this function returned "true". Although machines with many valves were known to have high failure rates, it was recognised that valve failures occurred most frequently with the current surge at power on, so the Colossus machines, once turned on, were never powered down unless they malfunctioned."

In summary, turn a tube power amp on and off because the output tubes pass a lot of current and will wear out if left on. With regard to most equipment using small-signal tubes, leave it on. For the record, I ran three tube preamps (CAT, Hovland and Jadis) 24/7 for a combined eight years, a DAC 24/7 for five years, and my current CD player, which has six-tubes in its output stage, 24/7 for one year - I have never lost a single tube or had any tube problems. I finally swapped out the tube in my DAC after many years just for the hell of it and it tested like a new tube. People lose small-signal tubes because they turn their equipment on and off.

Regarding your point about leaving digital gear generally turned on 24/7, absolutely leave it on - on/off turns a tolerable technology into a painful technology.

An excellent writeup by Raquel, and excellent advice.

For the record, though, I'd like to cite a couple of minor points that I believe are mis-stated.

Most small signal tubes that are used in audio components, such as the 12AX7's and 6SN7's, use indirectly heated cathodes (meaning that filament and cathode are different elements). The filaments in some designs are powered with low voltage ac supplied directly from a winding on the power transformer, in which case tube vs. solid state rectification has no bearing on the in-rush current to the filaments that occurs at turn-on. Better designs often incorporate dc filament supplies, in which case the design may provide better in-rush control.

In either case, controlled ramp-up of the rectified high voltage that is applied to the plate circuits (that can be provided for in the design of a good solid state rectifier circuit, or that occurs naturally with tube rectification) prevents plate voltage from being applied before some degree of warmup of the filament (and consequently the cathode) has occurred. Application of high voltage to the plate (or screen, or other high voltage elements, if present), prior to establishment of what is called a protective "space charge" of electrons around the cathode, leads to a phenomenon called "cathode stripping," which in the case of some tubes can shorten tube life considerably (although its significance in the case of small signal tubes is controversial).

Cathode stripping occurs, I believe, as a result of stray gas molecules in the tube being positively ionized by collisions with electrons being drawn toward the positively charged plate, the collisions causing electrons in those molecules to be knocked away. The positively charged, heavy, ions are attracted by the cathode due to its low potential, where their impact would damage the cathode's emissive surface over time were it not protected by the space charge.

Again, thanks to Raquel for the excellent writeup.

Regards,
-- Al

Great posts, thank you! Thanks Raquel for the thorough discussion and to Al for the physics lesson! I previously used a hybrid integrated amp with 7308 tubes in preamp stage and a Consonance 2.2 CD player with tubes in output stage and left those on all the time for a few years without a problem. But when I got the new CD player I was informed to turn it off when not in use. However, I have left the Ayon on for a couple of days now as an experiment, so look forward to listening for changes in sound this weekend.