Now we know where that "warm British jacket" comes from! The pair worked wonderfully and sounded terrific in our professional studio setup for monitoring. Input: Cambridge Audio CXC V2 dedicated CD transport + Schiit Audio Bifrost 2 Multibit DAC.
Amplification: Liquid Platinum Tube Amplifier by Alex Cavalli. Output: Focal Clear MG Pro open-back headphones. Our full tube sound review was written 100% based on the actual listening experience while this pair of tubes were running in the system described above. Both tubes tested Strong NOS (110%+ nominal mutual conductance) on a Mercury 2000 tube tester with the following result (mutual conductance in uMhos and percentage of nominal). Tube 1: 14,900/15,500 (119%/124%). Tube 2: 15,000/15,600 (120%/125%). Good tubes start at 7000 and new tubes incl. NOS/NIB 12,500 - 13,000, and the Mercury 2000's rated mutual conductance (nominal) for new tubes is 12,500. Test result can also be seen in the pictures. In case you wonder what all these numbers would mean to your sound experience, it's actually quite straightforward: mutual conductance directly translates to a tube's ability to amplify sound so the higher the numbers the stronger.We treasure this pair also because of the pristine condition of both tubes - over 90% of the paint and lettering are well retained. The Mitcham date codes painted glass are also visible on both tubes. B4E3 (B = Blackburn, 4 = 1964, E = May, 3 = Week 3 of the production month).