[FullRangeMan]

Interesting 6SN7 test from Mappletree audio:
A 6SN7/12SN7 mini-shootout with the Mapletree Ultra4A or
Line2A
Preamps are ideal platforms for conducting listening tests with different medium mu dual triodes of the SN7GT type. The heater voltage switch on the newer models enables an easy changeover between 12 V and 6 V heater types. On a hot summer afternoon, my friend Christian and I dragged out the equipment needed and set it up in the Mapletree shop, built into one section of a nineteenth century barn. The sounds from the horses directly below only added to the relaxed atmosphere. We set up a pair of PSB Alpha speakers on old tube caddies at one end of the shop, not particularly close to the end wall and canted slightly in wards. We sat about 12 feet away. The power amplifier was a Dynaco Stereo70 modified to use the new Mapletree Special Red driver board. The source was an
Optimus CD3400 portable with outboard regulated 6 V power supply. It fed an Ultra 4A SE preamp line input. The program material was track 5 Instrumental Medley from American Dreamer
 –
Songs of Stephen Foster (Angel). There was no attempt at double-blind (so-called “objective”) testing so the results are highly subjective which in many case only serves to highlight the differences which are generally subtle. Here are the results in terms of comments from the two listeners for each tube pair tried. We did not hesitate to go back for a second listen or to reserve judgement on a particular pair until others were auditioned.

[FullRangeMan]

Conclusions
Some of these tubes really catch your attention and make you want to listen to more. The Hitachi is a good
example. Japanese versions of N. American tubes don’t have a great reputation but these are very dynamic and
exciting to listen to. The overall balance and effortless smoothness of the 12SX7s and older RCA 6SN7GTs is
quite noticeable. I liked the Russian red base versions but not the black base ones. The former had the best
detail resolution of all the tubes tried. We would have liked to try some Sylvania and some RCA JAN but the
pairs on hand were not perfect matches so we passed. There are so many physical variants of these tube types
that two tubes coming from what look like identical boxes of the same vintage are often entirely different in
appearance, some differing in overall height (glass pinch vs glass button construction), base height, and
orientation of the two triode structures. If you want to try the Hitachi 12SN7GTs, several suppliers are currently
offering these at very reasonable prices. The Hit-Ray brand is identical.

[DaveC113]

Without pics and construction details of the tubes tested it's pretty much useless.

If I was looking to buy 6SN7 I'd look at Sylvania GTA w/ black triangular plates or the metal-base Soviet version with black plates/no holes. These are better than average tubes without getting too expensive, but tbh most 6SN7 sound good, and in some circuits the differences will be less noticeable than others.

[FullRangeMan]

You want pics? Your wish be granted>
Russian 6H8C Novosibirsk plant black base:

Russian 6H8C MELZ metal base: