Black glass KenRad 6SN7s take the cake

D_t_m- the 5692 & 5691 are more neutral sounding and usually
have a lower noise floor and are less prone to vibration.

If you get a chance check out the RCA brown base.

The Clear Glass KenRad VT-231's and 6SN7GT's are not even close to the Black Glass versions. It's a night and day difference. Compared to the Black Glass, the clear is 2 dimensional, thin and quite unnatural sounding. If you've been listening to the clear glass, you're in for a real treat when you try the Black.

Also noteworthy, the Black Glass VT-231 is different than the standard 6SN7GT. While I think the VT-231's are a bit better overall, the lower through upper midrange of the standard 6SN7GT's is stunningly accurate. The timbre is as perfect as I've heard from any tube. Unfortunately, it does tend to roll off the highs more and you loose a sense of air. The mids of the VT-231 is a wee-bit more shallow - (less weight and body & a bit less organic) - in the mids by comparison. But the VT-231's highs are more extended so you will not loose the sense of air. As in everything there are trade-offs.

As far as I am concerned, the Ken Rad Black Glass is easily the finest 6SN7 tube available.

BWhite and others, have you tried the National Union black glass or grey glass?

Gunbei, YES! The increase in qualities is exactly that. I didn't say so because my experience with the Slv is less (I have 3 NOS matched pairs but once the KenRads went in, I didn't spend as much time with them as I normally would have) and, also, people start thinking you're a Mister tube-know-it-all if you go around splitting hairs that much, which becomes counter-productive to the discussion.

IMO Black glass Ken increase is even more evident than that from clear Ken to Syl VT231. In quanititative terms - if you were going to point to all the audio language we use - then the increase seems continuous and of the same fabric (and it is...). But in qualitative sense - how you react to the sound, whether "musicality" increases, whether the change catalyzes one to "let go" of thinking and sink into the music - I think with the black Ken the curve becomes increasingly progressive.

bwhite is correct, although the system he constructed is allowing him to hear the differences more than most would :0)[his Supratek pre having a lot to do with it; happy now bwhite?]. Basically, in our language terms, tons-o-air and stretching back into large, voluminous depth field that offers the simulcrum of infinite dissipation of harmonics (er, our reality is infinite, so having that quality simulated is, er, a good thing; as opposed to bounded space which is not reflective of whats "real"). Highs sweeter, much more pure, distortive noise floor lowered revealing low level nuance, but not at expense of denuding space into a sterile void (also not a "real" experience, and what most people in the "accuracy school" refer to when they say their noise floor has been lessened). Space is lush and pressurized. Bass, while somewhat plummy in comparison to, say, the precision of a vintage Brimar, is homeric in proportion and how drums sound subliminally real (see, Braveheart and Gladiator CD's for this). Can impart feeling of longing into intruments and performances when it is there. Breath transients contain wetness; chest has volume; cellos have body (major difference with Syl VT 231, also reflected in highs, although I would not characterize them as "thin" in an harmonic sense, but lacking the same projection characteristics as the remainder of the spectrum, and further as you go up).

Got you drooling yet?

Yes, I'm talking about the mil-spec circa 1942-44 "VT231" black glass Ken Rad.

You know, it just occured to me that I'm not doing myself any favors on getting some of these in the future...

There's a long, thin, clear drool sling attached to the left corner of my mouth making it's way to the floor. :•)