The quietest 12AX7 tubes I had were selected RCA NOS from Andy at Vintage Tube Services
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I had a man on the inside at NASA maintenance in the 70s and 80s who provided me with a steady stream of Miltary grade 12AX7WA tubes, Sylvania and RCA, these are the quietest I.e., low noise 12AX7s I’ve tried although Telefunkens are not chopped liver. Even the low microphonic tubes, however, benefit from Herbies tube dampers. So, you’re never totally in the clear.