Despite of the general rave, the Tesla 12AX7 tubes' performance differs from a tube to a tube.
My first bought pair was not up to the expectation.
Its amplification factor is on the low side in coparison to 12AX7 tubes with a long plate.
Besides, its sound is too tamed to be dynamic nor rhythmic.
Certainly, it is a quiet tube, but the primary reason to listening music is not to listen quietness, but to listen music.
The particular pair did not sound musical nor detailed.