Returning to my above post, I want to reemphasize the point about the importance of leaving small-signal tube gear (e.g., tube preamps and tubed CD players) powered up 24/7, and not because it sounds better, but to EXTEND TUBE LIFE.
Quoting from the "TIPS & ADVICE" section of the owner's manual to my VAC Renaissance tube amp:
"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 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 computer:
"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 yearnearly 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."
Expanding on this point, Kevin Hayes of VAC states that with gear using small-signal tubes, if left on 24/7, defective tubes will generally die within the first 200-250 hours due to "infant mortality", while normal tubes will last years and years.
I never powered down my three tube preamps (Jadis, CAT and Hovland) or my tubed DAC. In a combined thirteen years of continuous operation, I never lost a tube - not one - and only retubed if I sold the piece, which I did only to make the piece easier to sell.
Except where the power supply also contains tubes, tube preamps should be left powered up 24/7, with the volume turned all the way down and/or mute engaged when not in use. Digital gear with tubes in the circuit should simply be left turned on (as should digital gear without tubes).
Quoting from the "TIPS & ADVICE" section of the owner's manual to my VAC Renaissance tube amp:
"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 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 computer:
"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 yearnearly 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."
Expanding on this point, Kevin Hayes of VAC states that with gear using small-signal tubes, if left on 24/7, defective tubes will generally die within the first 200-250 hours due to "infant mortality", while normal tubes will last years and years.
I never powered down my three tube preamps (Jadis, CAT and Hovland) or my tubed DAC. In a combined thirteen years of continuous operation, I never lost a tube - not one - and only retubed if I sold the piece, which I did only to make the piece easier to sell.
Except where the power supply also contains tubes, tube preamps should be left powered up 24/7, with the volume turned all the way down and/or mute engaged when not in use. Digital gear with tubes in the circuit should simply be left turned on (as should digital gear without tubes).