six year old 6sn7's, pushing my luck?

I retubed my Cary SLP-05 with Pope tubes about 5 years ago. I leave the preamp on pretty much all the time except when I go on vacation. That comes to about....45,000 hours. The tubes are supposed to be good for 10,000.

And...I've experienced no noticeable degradation in the sound. I heard a clicking sound once when I turned the system on after a week's time off, but I jiggled the offending tube and the sound stopped.

I've experienced tube failure and noise and rush in other systems, but this one seems to be the Energizer Bunny of tubesets.

I wish those Pope tubes were still available for a reasonable price, but Upscale now wants $275 per tube, and I need 6 -- I just cant justify 1650 to retube the preamp, but for now maybe I don't need to.

Any thoughts on this? Have you had tubes that lasted like this? Could they be degrading so slowly that I don't notice? Am I taking any chances with my equipment?

Thanks much and happy new year!


Showing 1 response by raquel

Dearing is correct about the care of small-signal tubes - provided they are not run in a circuit at near maximum voltage, which exposes them to a lot of heat, they will generally last longer than they would if you turn the unit on and off.

That said, Larryi mentions that the Cary has tube rectification. As Dearing notes, tubes in a power supply can be run hard and this complicates the question of whether to run the Cary 24/7. In addition, Larryi says that the Cary features soft-start, which, assuming proper functioning, eliminates the damaging voltage rush that occurs at power up.

The best way to determine whether 24/7 operation is best in this unit is to begin by retubing it - that way, you are starting with tubes that have not been damaged by previous on/off operation. Then just try it. Kevin Hayes of VAC, who is generally an advocate of 24/7 operation of small-signal tubes, explains that when run 24/7, small-signal tubes either die within the first 250 hours or so from "infant mortality" or they last basically forever. 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).