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signs that tubes need to be replaced

I have a pair of Cary Audio Six pacs which i bought used about a year ago. They mate well with my tube preamp and i couldn't be more pleased with the setup i have.  I dont know the number of hours on the EL 34s that came with the amps. The previous owner may have replaced them at one time since they look like they were sourced from Tubeco.I have them biased at the recommended 220 ma. and put about 300 hrs/yr on them. Question is, what should I be looking for (sonically) besides obvious tube failure that would signify the tubes are nearing the end of their useful life? Will inability to maintain bias be any indication?

Thanks,
J.Chip
128x128jchiappinelli
petg60
1,486 posts
 
HI,
When output tubes are difficult to bias then is a good time to replace. That will happen before losing dynamics, highs, bass and sounding muddy. You know that end of service life is close and it is better to have a spare set to check it. Better safe than leave them on till last moment. Visual check is not always the best guide but if the getters are not shiny any more and the silver layer at top of glass has gone off is a sign for replacement.
schubert
7,386 posts
 
Turn  system on and listen for rush sound which = dying tune .

oddiofyl's avatar
oddiofyl
3,702 posts
 
Sorry for the delay... those tubes didn't wow me at all at first.   I also was waiting for input and driver tubes before any real judgment 

So amps are freshly re tubed with over 100 hours and they sound great.   The bass is probably better than any other tube and it is balanced JUST RIGHT.   They sound great.   Think EL34 on steroids

I just pulled some tired KT88 out and these to me are better sounding in the QS Mids.   I think I just prefer EL34. Its almost like a hybrid of the best of EL34 and 6L6 
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