2. amps-preamps
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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
roberjerman
4,319 posts
 
When the silver getter flashes start turning brown at the edges! Eventually all the silver will turn to brown. That is the sign of "old age" - even though the tube will still work!
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decooney
2,034 posts
 

The same exact same Ruby EL34-BSTR (formerly Shuguang Factory made for Ruby batches), same tubes in the Cary SixPacs were also used in my Cary V12R amp.

Don’t underestimate these particular -bstr tubes due to the lower price point. These amps were designed and voiced with them and actually sounded fantastic! Similar reports over the years from friends with same amps. Grab ’em if you can find them, supply was kinda drying up on the BSTR version Ruby’s for a while. Did a search today, fewer carrying them as before. Look for the -bstr version. Snatch up three quads.. good luck.




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 .

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