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Tube lifetime

Using the search term "longevity" and searching in the "tubes" forum does bring up some results. Try searching for "posts" rather than "threads" (the default).

I do think though, that you are asking "how long is a piece of string".... ( I use such a metaphor in the knowledge that the Dutch people understand English as well as many English people).

I know the expectancy is largely dependent on the use and bias, etc. But just a list with averages would be very welcome:

300B ....hours
El84 .....
KT88 ....

Noobishly enough this would help me a lot. lifetime is not given in data sheets...This amazes me, not even a minimum within normal use. It's rather usefull for me comparing tube amp's and cost of use.

Regards and no harm done with the how long is a string remark.

Tube longevity

Military specs for tubes often give a guaranteed minimum lifetime (usually spec'd as gm falling to a certain minimum value). Both American and Soviet data sheets show minimums ranging from 500 hours for RF tubes being pushed hard to 1000 or 2000 hours for average tubes to 10,000 hours for special high-reliability tubes. The actual lifetimes are typically longer.

Now for some real-life experience. When I was in college at Columbia University in New York (from 1971 to 1976), I had a part-time job working for the music department and the Columbia-Princeton Electronic Music Center. Me and two other colleagues were responsible for keeping all the music-related electronics working at both Columbia and Barnard College. For most of the music class-rooms and libraries, Columbia had standardized on the following equipment: Dynaco PAS preamps and Stereo 70 power amps (with a few Mark IIIs and ST-35s in the mix), KLH-6 loudspeakers, and AR turntables with various Shure cartridges. The electronic music studios had more sophisticated equipment, dominated by Ampex tape recorders. We were beginning to install solid-state equipment while I was there, but most were still using tubes.

Every summer, I carried a Hickok 6000 tube tester around the campus and tested all the tubes. Any weak ones were replaced. Of course we replaced gross failures right away if equipment went down. The music classrooms and libraries were typically in use at least 12 hours a day, 5 to 6 days a week and the electronic music studios were in use for at least 18 hours a day, 7 days a week.

Here are my memories on tube reliability. Keep in mind that we were using what we would consider today expensive NOS tubes, i.e. Mullard and/or Amperex European types and RCA American types. The EL34s and GZ34s seemed to last at least several years- maybe averaging about 4 years. The 7199s in the Stereo 70s and 6AN8s in the Mark IIIs usually lasted little more than a year. And the original Dynaco-branded smooth-plate Telefunkens ECC83s that were in the PAS preamps never died! On my last tube-testing rounds in the summer of 1976, virtually all of the Telefunkens that were in PAS preamps that had been installed in the early 1960s were still going strong! The Amperex and Mullard ECC83s lasted about 5 to 10 years. Given the heavy use of this equipment, this was pretty good.

I hope this gives you an idea of real-life reliability. Just because a tube still tests good doesn't mean that it will sound the best, though. Also, some contemporary equipment grossly over-stresses the tubes, leading to short lifetimes. Avoid this equipment.

- John Atwood
1000-10,000 hours is a very accurate range IMO as well. Output tubes on the lower end, small tubes on the higher end of that.

Older US and European tubes seem to last longer than some of the new production tubes. I think this is purposely designed that way too, modern tube companies are selling far less volume of tubes, so they need more turnover to generate and maintain income levels.

Still, run within specs, any tube should deliver a life long enough to warrant its cost. Run 3 hours a day, every day is about 1000 hours a year. So, even a poor performance is at least a year of daily listening, for what, about $15-$25 a tube? That's not a bad return, even in the worst case.

Now, as for when they are changed vs. really die, The tubes will work far longer than I would keep them. Once the audio properties have deteriorated, I change tubes, again, this is still a very, very long time. The fact is though, audio performance will decline over life... how fast or how much depends on the actual tube in question.