Hi Gang. In reference to Casouza's post stating the 6sn7 as a direct decendent of the 6sn7.
Although electrically equivalent and both employ the same octal base, the 6j5 is a single triode whereby the 6sn7 is a dual triode [basically two 6j5's in one tube] and are not direct substitutions.
While there are so many different flavours to experience in the 6sn7 family of dual triodes, and as mentioned by Ait in an earlier post.
In my experience, the 7193 is sonically superior to any 6sn7 regardless of manufacture... nos or otherwise.
Comparatively speaking: the 7193's sonic signature is a combination of the best of the 6sn7 family.
Combine the bass power and depth of the Kenrad black, the 3 dimentional midrange of the old tungsol round plate,the bloom of the Rca grey glass with the treble extention of the best nos sylvania's.
Although a little more difficult to find these days, they generally sell for a fraction of the cost of the nos 6sn7's.