Black glass KenRad 6SN7s take the cake

I've been experimenting with 6SN7s in my VAC 70/70:

ElectroHarmonix: good tube! and great for the price. Much better than I though it'd be, but ultimately sounded too edgy and sterile. Good control throughout, and good detail.

Sylvania VT231: twinkly and brilliant; great detail, tight bass, but much less fatiguing than the ElectroHarmonix; nice and smooth, but still lacking in the mids for me.

TungSol black glass, round getter: better than the Sylvania, in that it was a bigger sound. Lost the twinkly and brilliant quality. Good detail. Good overall, balanced tube. Nothing outstanding I thought, relative to the other tubes I tried.

KenRad, tall, black glass: THESE KICK!! very lush, deep, BIG BIG sound; the absolute best midrange; detail was good, and surprisingly, this tube is NOT DARK. very smooth, and less reserved sounding than the other tubes. Let's it loose... and that's the one drawback; the bass isn't as tight the TungSol or the Sylvania, but it didn't annoy me. What I gained from this tube far outweighed this drawback.

...that's just what I thought of these tubes in MY system. Who knows if these qualities translate to other pieces.
D46058ba 24d0 4dd9 8a2d 4f6ded3d8fe0dennis_the_menace
Dennis the Mennis

Where did you buy the Ken Rads and how much did you pay for them?

That is the exact quality I like too - big midrange and dynamic if I read your post right.

thanks for sharing
Got them off of ebay from this guy called "romhifi". Sounded like he had different stashes of tubes, including some National Union black glass that I wanted to try next if the KenRads didn't work out. He may have some more KenRads....

You could probably get some responses by posting a "wanted" here on Audiogon.
Dennis, my impression of the NOS Tung-Sols and Sylvania VT-231s mirrors yours in my Blue Circle BC21. Early this past spring when I was buying up tubes on Audiogon, I managed to snag three NOS US Navy Ken-Rad VT-231s dated January and February 1945. I've enjoyed the Sylvanias so much that I stopped rolling the tubes in my BC21, but I've always wanted the qualities you describe in the Ken-Rads. The Ken-Rads will be going in my Blue Circle right now, I'll report back in a few days.
Dennis-have you tried mixing the 6sn7s you have? I have a VAC 30/30 and spent considerable time rolling different 6sn7s I have, many of the types you comment on above. I find most of your comments on the money. In my system, the best combination were the sylvania Vt-231s on the inputs and the Ken Rads on the outputs of my 30/30. Give it a try, you may find it to your liking as well.
Also had good luck getting 6SN7's from romhifi on Ebay.
Pgleekel... which of the 6SN7s are the inputs, and which are the output? Has anyone tried the National Union black glass?
KenRad black glass are extremely fine. I have four NOS 1944 matched pairs, army boxes, that I am still glad I accumulated at the time. I use the Tungsol round getter black glass, but only because speakers in that particular system are not full range (Tungs sound sweeter there, although not as expansive as Kens).

You guys may want to take a look at the "Preamp of the Century" thread. The Supratek pre takes 6SN7's and we discussed them there about a month ago. My impressions and others are there FYI.

denis, what tube did you eventually end up with as outputs on the 70/70? Svets? Happy?
For now, I'm running the VAC with 4 Western Electric and 4 Golden Dragons. I've got 8 JJs coming soon. The Golden Dragons are on their last leg. I love the sound so far... the KenRads took it up one more notch.

Next year, once the Supratek comes, will be another flurry of experimenting, I'm sure.
Dennis- at least on the 30/30, the inputs are the two inner most 6sn7s and the outputs are the two outer most. I only assume the 70/70 is set up the same way.
Well, I've had some clear glass Ken-Rad VT-231s burning in my system since Wednesday, and had my first listen this Saturday morning.

In my system they do indeed sound big, lush and not dark at all. They don't have the top end detail of the Sylvania VT-231s, and that may be the reason I feel they aren't as holographic, but I like the Ken-Rads very much. Their midrange is very organic. Female voices sound more like the singer is in your room unmiked, whereas the extra detail of the Sylvanias make you feel the singer has her lips close to the microphone. Only you can decide which is better. These are real keepers!

I wonder what the difference is between these and the black glass Ken-Rads.
Ken Rad Black glass discernibly better...Huge depth, expansive, quieter, low level detail more natural, harmonic decay improved, Homeric bass, even more organic while still clearer into depthfield without any increase in sterilty. Sounds very similar in all parameters - as you would expect - but involve-ability is heightened, making any deficiciencies at the frequency extremes (full toward plummy bass in some systems; slight rolling at very top but not thin, just reduced projection) a non-issue IMHO.
D_t_m- have you ever tried any mil spec 5692 in place of
the 6SN7s?
No, haven't tried any 5692... but I'd be curious to hear your opinions on them. Have an opportunity to get some National Union black glass... think I may wait until I get the preamp that needs a 6SN7 before I invest anymore in 6SN7s. The kenrads are really awesome...
Asa, the characteristics you're describing seem very much like the differences I hear between Sylvania VT-231s and the clear glass Ken-Rad VT-231s I'm currently comparing. Are you saying that the black glass Ken-Rads have even more of what you're decribing over the clear glass? After trying the Ken-Rads for a week, it's a little tough listening to the Sylvanias, they seem more detailed, but also quite thin in comparison.
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. :•)
Give me the Sylvania 1940s 6SN7 WGT any day. IMO the best there is. If you really want to hear what a 6SN7 can do, just listen to it as an output triode in a Berning Micro ZOTL, driving a pair of Lowthers direct. This is where you really hear the soul of the tube, with nothing between the tube and the speaker but a few feet of wire. Nothing after it in the circuit at all. Pure 6SN7 coming out the single drivers. The Sylvania does it all. I swear I can tell when Rickie Lee Jones casts a quick glance at the band and smiles as she says, "Chicken in the pot, Chicken in the pot" on Danny's All Star Joint. Now that is seeing into the music. You can actually tell she's smiling because of the slight affectation of the vocal, caused by the smile shape of her mouth as she sings it. I'm not kidding.
twl, now I'm smiling. :0)

Question though: What were your comparitive observations - the differences between the Syl VT231 and the black glass Ken-Rads - when you put them both in your newly arrived amp?
Asa, I did not use the 231, I used the WGT version. And the sound difference was amazing. The observations made by others regarding the delicacy of detail, midrange liquidity, strong bottom end, crystal-clear high end were all there, far better than any other tube I've used in it. Now perhaps with preamps, where it is combined with other circuits, and passed through a power amp on the way to the speaker, there could be some "synergy" considerations that I didn't encounter on my system. The Berning MicroZOTL is the only amp ever to use a 6SN7 as an output triode, as far as I know, and it uses it in a push-pull arrangement with each 1/2 of the twin-triodes inside the single glass envelope performing the push-pull functions. Linearity is excellent with this configuration, and gives teriffic frequency extension on both ends, and of course, no output transformer to saturate or cause hysteresis problems. Now, as I stated, this is a different application of the tube, but I did not get as good overall sound from the Black Glass KenRad in my application, although it was very good sounding with them. The KenRad, Sylvania WGT, GTA and GTB, RCA Black Plate 5692, all were far superior to the stock Sovteks that came with the amp, and would all be a big improvement. I was more disappointed with the 5692 than anything, as it was well balanced, but did not have any real "twinkle" like these others had. And there is a definite difference between the Sylvania stuff, as the years went by. The older is decidedly better, and after the 1st couple of years of the GTB, it was a bad downhill slide. The 6SN7 W and WGT from the 40's are the best, and then the 50's, and then the early 60's chromedomes in the GTA version, and finally the early GTB. Later GTB were not nearly as good. I have not tried the very early metal-base version, although I have heard they are very good. I also did not try the Clear Glass KenRad. As they say, YMMV, and this is only my opinion.
Twl- Have never seen a "black base RCA 5692." The red base
RCA 5692s that were used in my MFA electronics(preamp & amp front end) had plenty detail.

Very interesed in your speaker system. Where can I get
details on the drivers and cabinets?

Kana813, I referred to Black Plate 5692, not black base, although there are black base RCA 5692 tubes. The Red Base 5692 is the famous "sought after" one, but there are non red ones also. Also the "Black Plates" are actually really deep charcoal grey.

My speakers are Voigt Pipes that use Lowther EX3 drivers. You can find info on the drivers here:

And you can find Voigt Pipe plans here:

The Voigt Pipe plans shown here are the same as what I used from the Lowther Club of Norway, but this guy used a Radio Shack speaker in his. It doesn't matter, the dimensions are exactly the same.
The Lowther Club of Norway has removed the plans from their site.
If you are going to make these you should contact me when you get ready to do it. I've been down the road.

The sound is awesome for low-power SET amps. Of course, the bass is quite sharply rolled off below 40Hz, but I don't miss that too much. Even the really good multi-way designs don't really go too much lower than that, in reality. Most are -3db at 32 or 28Hz. Unless you listen to alot of organ music, you'll never know it. The lowest note of a bass guitar is 41Hz, so if you mostly listen to popular music, its fine. That's only half an octave less bass in the least used area for music. The rest of the spectrum is spectacular, and the imaging is the best. Small sweet spot, due to directionality. Incredible dynamics and detail. Totally coherent. High end goes to 20kHz. Get the new series of drivers, as the previous upper midrange anomalies have been worked out. Don't buy a used pair over 6 months old. New is best. The EX3 will cost $895/pr and will give 100db with 1 watt input, when loaded into the Voigt Pipe cabinets. A 45 or 2A3 amp is plenty. A 300B is more than you need, but still sounds great. I ran them on 1 watt for 6 months with my MicroZOTL, but I felt I needed a little bit more headroom. My new Berning custom 45 amp will be here in a couple of weeks.

You can build the cabinets out of MDF for under $100. If you want fancy wood, you can do that too, but it costs more. I recommend that you at least make the front panels out of a good hardwood. It looks better, and it takes away a little harshness that the MDF has. I used oak fronts and MDF backs, and they look great and sound great. I also made a modification to mine that reduces the baffle-step effect under 380Hz. Due to the narrow cabinet design, the baffle reinforcement of the frequencies under 380Hz drops off due to wavelength. By adding some "swinging doors" to each side of the Pipe, you can bolster the mid-bass frequencies, and make the frequency response alot smoother in this area. Also, since they swing, you can tailor the backward angle on both sides to give adjustability to your midbass response, and tailor it to the music and to the room needs. If you need more info on this mod, email me for details. I have been living with these for about 6 months now, and I have no desire to look at any other speakers. These give me everything I need.
twl, I thought about "synergy" on pre input vs. amp output, but concluded that was a red herring because, theoretically, and in my gut, I feel the pass through on the berning should be best - or at least good enough for you to base a broad opinion on the tubes versus each other.

Haven't looked at my SylVT231's in a while, but I know they are NOS in army boxes with original packing from 1942, so assumed those were the good ones...

If your WGT are different, I am, of course, intrigued; always looking to learn something.

On the metal base, I never wanted to pony up, but a few who did with the Supratek thought they were not what everyone has said. Maybe the rep comes from pro guys, or the Glass Audio article a few years ago, but people's consistent reaction, coupled with the cost, made it easier for me to back away.
How about those black glass National Unions? Anyone try and compare those to the black glass KenRad VT231?
Asa, my WGT are Navy types from WW2. I expect that they would sound very similar, if not identical to the VT231 army issue. The "W" designation is also a mil-spec suffix. I am not sure what the mil-spec difference is between W and VT231. I know my WGT were Navy sonar tubes. Since you already have VT231's, I don't think it would be worth moving to the W or WGT, because I don't really know that you would be gaining anything. If it was strictly for curiosity's sake, that may be worthwhile. At any rate, I would be quite satisfied myself with a good pair of VT231's from that time period.
Dennis, I believe National Union was a company which put its name on other manufacturers tubes. If you speaking of the NU 6SN7's on Ebay now, they appear to be Tung Sol Round Plates which are good tubes.
Wow this a thread I can really sink my teeth into! I agree 110% with Twl. I have two pairs of the wgt's and they sing. I had a pair of the VT231's but they didn't faze me. Funny thing that version I had was not a mil spec tube. It had the same construction and from what I gathered syl made some for consumer use. What's everybody take on the grey glass rca's?
The National Union's I'm talking about are vt231s, black glass... supposedly much like the KenRads.
Has anyone used the Ken Rad's in a Rogue 99 pre and how would the KR's compare to the Russian nos 6sn7's in my 99 pre currently?