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

Showing 2 responses by tpsonic

The offers I posted on, use the 6as7,6c33c-b and the EL-509/519s.The last are probably the hardest to find,but I understand that Transcendant carries the tubes for his amplifiers.
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.