SET Asylum

Not a Dumb Question; a Tough Question

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In Reply to: RE: Dumb question - how to tell valves are spent? posted by Neillo on November 28, 2007 at 10:54:41

Taking your questions and comments in reverse order:

To state the obvious, if you're noticing that "the amps seem much less enjoyable," then something's wrong. Sure, it could be that your output tubes are past their prime; but, it could be any number of other things as well. I admit that the fact that we're talking about monoblocs strongly suggests the former -- as you suspect. But, it still seems strange to me that you would be detecting a normally long-lived tube deteriorating. (More on that below.)

I'm going to assume that you didn't get Western Electric's predicted 40,000 hours out of your 300Bs :-) It could be a quality issue; i.e., EHs are not WEs. It could be an operational issue; i.e., Cary monoblocs run tubes a lot harder than WE theater amps ever did. With that, I know of people who lost EHs after a matter of some months and of others that have been running the same pair for years. (There's your quality -- or lack thereof -- issue.) But, Cary's design, itself -- by running output tubes at or close to their various maximum ratings -- might be responsible for *automatically* reducing 40,000 expected hours to 10,000 or 5,000 or 2,500 expected hours. (There's your operational issue.)

"Physical indicators" are notoriously misleading (to the extent that they even exist) -- especially when they accompany a slow death. That said, "sonic indicators" like tubes starting to sound tired and lifeless are hard to pick up on day-to-day. Long-life tubes like 300Bs age so slowly that only a stark comparison with a new pair would be particularly telling, IMO.

I wouldn't count on a tube tester to tell you when to change tubes, so I wouldn't worry about not having one. Sure, it's nice to know *before* you plug a tube into your amplifier that it has a short(!), but no tester is going to be able to tell you how a tube is going to sound -- assuming it meets some minimum criteria.

I would be interested to know how much use you've gotten out of the pair of 300Bs in question. In addition to that, I would be interested to know how much use Cary thinks you should expect from a pair of 300Bs in its monoblocs. Finally, since you're going to have to replace them at some point anyway -- and since the issue is now weighing on you -- you might think about buying a new pair (assuming you want to stick with EHs) and comparing?

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