I recently decided to buy a set of Platinum grade GT GT12AX7M from Upscale for the phono stage of my Janus. I've tried quite a number of NOS 12AX7s here, including Bugle Boys, Teles, Mullards, Mazdas and Ediswans. I can tell you without a shadow of a doubt that these tubes sound as good as any, and furthermore display the lowest noise levels of any of them (essential in the phono stage, not as critical in the line stage, which is inherently quiet). As good as these are, I see absolutely no reason to go hunting further.
At the same time, I bought a pair of what Kevin describes as 'Early Russian 6H23/6922 Type 3'. These are also excellent, but IMO do not affect the overall sound as much as the 12AX7s.
At the same time, I bought a pair of what Kevin describes as 'Early Russian 6H23/6922 Type 3'. These are also excellent, but IMO do not affect the overall sound as much as the 12AX7s.