Of the 4 NOS tubes ive tried so far ,including sylvania ,mullard and EH, the 1956 RCA black plate 12bh7A are the best by some margin.
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CTC Classic 301 , SPH bearing and Hanze Hifi HAT CPS-2 all analogue power supply / Tenuto Mk2 mat / custom Panzerholz and Kewasinga articulating plinth / Track audio isolation feet / Reed tonearm / Audio Technica ART 9 / 2 box BigBottle mk3 phonostage with Clarity cap CMR and NOS Telefunkens valves / Croft 25R preamp with upgraded 12BH7A line stage and NOS 1956 RCA valves / Croft 7R monoblocks with NOS 56 RCA valves/ Dynaudio Contour 30i speakers / Spotfire interconnects and speaker cables / Merlin Scorpion mains block / Rhodium mains cables / Marantz CD DAC /