Phono preamp tube rolling.

Yes, a holy grail Tung Sol 6SN7GT from the ’40s. Now listed on Ebay from $450 to $900 per pair.

It’s been a long time since I played with lots of vintage 6SN7, in a crazy headphone amp (and briefly later on in a Rogue 99 Magnum preamp). I do remember the Tung Sol BGRP sounded the most unique out of all, and the best to my ears. An extremely juicy, "technicolor" sound (like Koetsu) that was the only tube which seemed to fully deliver on the 6SN7’s purported promise as "king of tone". The Ken-Rad was my next favorite (especially BG variant), with bass 2nd only to the Tung-Sol. The Sylvania VT-231 seemed a little dry to me but was neutral and could be good in combination with Ken-Rad or Tung-Sol. I also liked the brown-base Sylvania 6SN7WGT, probably more than the tall bottle VT-231. I never liked the gray glass RCA VT-231 as much as these other makes, but it’s nonetheless a pretty good sounding tube. The Electro Harmonix 6SN7 sounded positively "solid-state" like by comparison.- a little grainy, and with a surplus of treble energy, but nice bass to balance it; honestly not too bad a tube for the money (and of course by now I’ve heard plenty of solid-state gear that is neither grainy nor bright). The Russian Tung-Sol 6SN7GTB sounds like a more refined version of the EH.

I also remember combining different makes seemed to stack only the positive attributes of each, rather than stacking or remixing the downsides (maybe this interesting quality is part of what makes 6SN7 so revered) - but if I’d ever had a full set of Tung-Sol BGRP, I probably would’ve just filled every slot with those. Problem is I kept getting used "nearly dead" ones that kept dying on me. It’s always been hard to find good ones and demand is so high people keep trying to offload duds.

For any of these old 1940s variants - GOOD LUCK finding a pair quiet enough to use in a phono stage or in the gain slot of a preamp. The old Sylvania 6SN7GTA/GTB 1950s "chrome domes" are easy enough to find quiet and in matched quantities, but aren’t as sweet sounding as the old tubes - they sound kinda like a slightly sweeter Russian Tung-Sol GTB in VAC 200iQ amps.

Now we are getting into the “icky” realm of ascribing magical sonic qualities to this or that tube based on loose subjective evidence or on hearsay evidence.  Why I stopped rolling tubes at all, once I figured out what I liked, of course. Changing a capacitor, for one example, can have a much more profound effect on SQ.  I guess it’s fun.

@mulveling 

the Tung Sol BGRP sounded the most unique out of all, and the best to my ears. An extremely juicy, "technicolor" sound (like Koetsu) that was the only tube which seemed to fully deliver on the 6SN7’s purported promise as "king of tone". The Ken-Rad was my next favorite (especially BG variant), with bass 2nd only to the Tung-Sol. The Sylvania VT-231 seemed a little dry to me but was neutral and could be good in combination with Ken-Rad or Tung-Sol. I also liked the brown-base Sylvania 6SN7WGT, probably more than the tall bottle VT-231. I never liked the gray glass RCA VT-231 as much as these other makes, but it’s nonetheless a pretty good sounding tube.

My thoughts exactly, even down to your remarks about the RCA VT-231.
Ken Rad Black Glass paired with a Sylvania VT-231 produces the best attributes of both tubes.

The only tube I've heard to rival the Tung Sol BGRP is the Melz 1578 OTK, Russian military. This is a magical sounding tube. I know these terms get thrown around, but a pair of these in my amp created a you are there experience, so realistic it was scary.

 Unfortunately, the early years were the best and they're all gone. I have some from 1980 and for a short time I was able to enjoy them before they crapped out. Have one pair that works and I'm saving it. 

@mulveling 

Melz 1578 OTK, Russian military

The stamp of “OTK” is not about the brand or any tech spec… at old Soviet and Russian manufacturing “OTK” means Department of Technical Control passage. Usually checked and ready to ship products was stamped with OTK stamp.