Phono preamp tube rolling.

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. 

Totally agree about a Cap' change having a profound effect.
The Phonostage I am using has been auditioned in various circuits for the end design to be produced.
When the prototype was almost complete and identified as being a very attractive performer.
Curiosity was still with myself and a couple of Cap' and Resistor changes were encouraged to be undertaken that had been discussed and not as yet trialled.
A Brand change of a Copper Cap with a different value and a few Z Foils was a remarkable change and the one I have maintained in my owned model.     

@lowrider57
I have a very good friend, younger and with better ears than mine - he says the exact same things about that Soviet 1578 tube. Yes the vintage/make is supposedly very specific and very important. Something abut round plate holes too, etc. I’d like to try them someday but understand they will be very hard to find (unless I can pry a pair off my friend), and my main system is not currently married to 6SN7 tubes.