2. amps-preamps
  3. 158704-127647

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

Showing 2 responses by oddiofyl

oddiofyl's avatar
oddiofyl
3,476 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 
oddiofyl's avatar
oddiofyl
3,476 posts
 
Drifting bias is a sure sign however that could also be caused by an out of spec bias resistor.    I had a matched quad of  EL34 power tubes that were about 8 months old.  One had "fire in the bottle" so to speak.  Literally arcs and sparks in one tube... it was scary.  Fortunately Quicksilver amps are robust and it only took out the mains fuse.   That was during play , it was sounding great and then all of a sudden horrible cracking noise through my speakers, I look up and fire....   I was lucky.  That said, I always try to replace before failure.  I have a set of KT88 that have a lot of miles on them and have been my spare a few times.  They still sound ok and hold bias but I'm nervous due to hours on them

I have a new quad of Gold Lion  KT77 on the way.  Hopefully they are as rugged and long lasting as they say
More to discover