Which Telefunken 12ax7

Generally the East German tubes have thinner pins. A reputable dealer (such as Brent Jesse, Vintage Tube Services, etc.) will not, or should not, steer you wrong. See if you can find some good testing used pulls from old equipment. You can then use those to compare such things as the pins.

Well, as it turns out, while I was seeking consensus on this forum, the particular Telefunkens that I was eyeballing were sold to a gentleman in Hong Kong (the quick and the dead). In lengthy conversation with Brent, we decided to start with a pair of 1953 Siemens ECC83 long plates. If they're not everything I'm looking for, I'll try the Mazda's. Thank you everyone; your help was more appreciated than you know.

I highly recommend NOS TESLA E83CC or like been stated above, truely Teles with Made in West Germany and dimond logo on bottom.

The Siemens have been breaking in for about 50 hours now and seem to be the ticket in my system. They are very detailed without being dry or bright. Definition, dynamics and accuracy of timbre have all been elevated to a level that now comes much closer to placing me before the artists. The bandwidth is astounding and perfect for my broad bandwidth amp. The soundstage is expansive. Most importantly, my attention is given entirely to the music.

One caveat: While it's all good here so far, I can imagine them seeming a little too thin in the wrong system. But still, I can't resist making the generalization that by pairing these with 300b's in push-pull, one has put together a dream team.

I have a pair of Raytheon 5751 black Plate with Windmill Getter. I upgraded from a Telefunken 12AX7 smooth plate and this one blew me away for its extremely low noise floor and ultra detailing, yet retaining a very liquid smooth sound. I have never looked back since then. I know someone who might have a pair, let me know if you want them.