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Tubeaholics please advise

I have the Counterpoint SA-4 OTL monoblock amps, which I bought retubed about 10 years ago, running Martin Logan CLS's. No problems so far, but the mileage is getting up there. You cannot bias the SA-4 tubes individually, so matched sets of tubes are recommended. They take 8 6LF6's per side, which I am now finding out are nearly impossible to find NOS in any quantity, and if you can find them, are going $100.+ per tube!
Issue: (1) should I buy a few used tubes and keep nursing the amps along, despite the fact the used tubes will not be matched? Or just start saving now for a new set of amps? (2) given that OTL amps can fry speakers when the tubes die, what are the telltale signs that a tube is about to go?
thanks guys!
stilts1
nsgarch's avatar
nsgarch
2,524 posts
 
If you love those amps with your CLSs (and you should!) have this guy upgrade them to the max, which includes a separate biasing unit that allows the use of unmatched 6LF6's:

http://www.altavistaaudio.com/SA-4.html
.
mcfarland
356 posts
 
I have a pair of friends who each has a large stash of vacuum tubes. I will check with them on the availability of the 6LF6 tubes which you require.
tpsonic
1,092 posts
 
They will glow more brightly,but you will probably notice that they are becoming noisy.When the tube goes,you will measure a DC offset voltage.
Transcendant Sound,Joule Electra,Atmoshere and Einstein also build OTLs.Please check the reputation of the importer for the Einstein gear out of Germany-don't know who it is.
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