Tubes begin dying on day #1 of use. After 1000 hrs., it`s conceivable it`s outputting 1/2 of rated pwr.
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Yeah, your assumptions are more or less correct. Aside from identifying shorts, each tube tester has its own standards for what is passable and excellent.
Tubes do burn out in varying degrees depending on the tube type and how it's being utilized. I have a DAC that uses two 6922s and I'd leave that DAC on 24/7 for three or four years with very little noticeable degredation of the tubes.
My preamp goes through 6SN7s much quicker. It may have to do with the ones I use all being WWII era tubes or maybe it could just be the way they're being employed in the design of the preamp. But it gets expensive.
Power tubes can be even more costly.
Depends totally on the particular tube type and the component in which it's used. I have some Telefunken 12AX7s that have been in regular use in my phonostage for over 10 years, and they were used tubes in the first place. Mullard EL-34s also seem to last virtually forever. Some components stress their tubes more than others. As far as the tester is concerned, the good and excellent ratings are too often arbitrary, depending on how the user interprets the meter and how the meter is marked (my own tester has no position higher than "good" ). You're better off paying higher tube prices to a trusted/respected tube seller. I've been lucky in buying tubes, and I've been unlucky. I wish you luck. Dave
Here's a follow up question; more specific I guess. I see lots of tubes with tester measurements such as, "1700/1700." Followed by a comment that 2500 is 100% or "65/65 where 140 is new."
Can I draw any real inferences from these? For example, if a 6SN7, assume, lasts 5000 hours, can I asume that a tube meauring 70/70 will only last 2500 hours??
Why are there two numbers?
There are two numbers because there are two tubes (triodes) per 6SN7. As to an earlier question of yours, the filiment usually does not burn out like a light bulb. What happens is the cathode coating slowly gets "poisoned" due to impurities at the time of manufacture. By the 1960s, they had figured out how to make tubes that would last for 100,000 hours. Think undersea cable amplifiers. But by then the transistor had taken over. Too bad for us tubeheads.
LOL @ Pawlowski6132!
My experience with 6SN7s dying is similar to Jburidan's except it seems to happen in one channel before the other. Also, if one channel starts crackling whenever you adjust the volume that could also be a sign of a tube going bad.
I really love the way 6SN7s sound, but in my set ups they seem to go bad much quicker than 6922s. It could also be the applications I had them in.