Listening for tube degradation

I also never had the equipment (or the knowledge) but learned a way after I made Heath and Dynakits, take cover off the amp and let it warm up,do not touch any part of the amp (be sure the selector switch is set to Lp or extra/cd whatever you are using, volume up a bit) and tap the tubes with a pencil. This may not tell you how much life is left in a tube as a Tester would, but if any tube makes any noise comming from the speaker when you tap it, static, spitting, burping, harmonics etc, it is done for and should be replaced.
Len W

Len W- not to be contrary, but what you are hearing is microphonics. Some tubes are microphonic when new, some are not. I don't know if this can also occur due to aging. It may be sign that the tube needs to be replaced, but it is NOT a reliable indication of aging. BTW, some microphonic tubes can benefit greatly from a tube damper.

Performance that deteriorates slowly, in tubes or anything else, is difficult for a user to recognize. Think about your eyes. They seem to be OK until the optometrist says you need new glasses. One nice thing about ss amps is that, unless they emit a puff of blue smoke, they are probably OK. With tubes I found that I was constantly worrying about them, listening for problems, which detracted from the musical experience.

I agree with Eldartford, most often tube performance deteriorates slowly. Some can last a year while others may survive 20 years. Too many variables about circuit application, user care, etc. so time alone cannot be the measure.

I believe anyone with more than say 2-3 tubes in their system should try to find a tube tester and learn to use it. I'm not knowledgeable about electronics but I found a B&K tester at a swap meet and bought the tube charts and calibration instructions from them. That was a few years ago but the $ and effort paid for itself many times over.

Treat your tubed components just like you do your car. Simply put them on a maintenance schedule and routinely replace the tubes accordingly. I replace power tubes at about 2000 hours. This takes care of incurring a serious loss of sonics, or major shorts, due to age. I replace my small tubes, depending on use, about every 4000 hours.

Some may consider this early, but at least I don't worry about subtle degredation in the sound quality. Why invest all that money in audio stuff and then cheap out on the tubes by seeing how long they will last

Oh, power tubes lose bias as they age and you will find that you need to increase bias (ma's) as the tube ages. If you let them age enuf you will be unable to get the up to recommended bias settings.

Small tubes can get noisy and or dullish, i.e. loss of detail with age! I replace them all at the same time if it is a noise issue related to age to retain good channel balance.

FWIW.