Steve Deckert
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There are 3 grades of this tube. All are N.O.S. Russian tubes that were made until 1986. When I started manufacturing the Zen amps there were confirmed at least 10,000 of these tubes available. The highest grade is a mil spec tube with higher impact ratings and longer life. The number of these tubes remains unknown. They were never branded with the Svetlana brand. The original Svetlana branded tubes are mostly owned by our customers leaving about 2000 of the original 10,000 still floating around. Since New Sensor purchased the Svetlana name a few years back, the consistency of the original batch was lost so I stopped purchasing them.
We only buy the top grade mil spec 6P15P-EV aka 6n15n-EB tubes directly from Russia and Europe for all of our production amplifiers that use that tube.
Steve
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