Fantastic write up!
Always a pleasure to read articles like this.
I become interested in getting some of these adapters just to dip my toes into the neverland of new tubes
7N7-CF8G-6CG7 Lets Do This...
7N7 1950's (Philco, Sylvania)
I can only imagine what a FRANKENTUBE would sound like as the tall tubes in my possession lack the very flat top tube appearance. As they are now, they sound incredible. Instrument separation above average, and lively.
7N7-CF8G-6CG7 Lets Do This...
So I've been wanting to do this rolling session for awhile and with my little knowledge on adapters it took some time to get these all together for this comparison write up. Before we get knee deep into this I decided to exclude the 12AT7 as it has no breath of air to be considered for this roll up... it's gonna be super hard for me to express in adjectives on the remaining three tube types, The 7N7, CF8G , and 6CG7. All of these exude that open airiness, So lets begin this tough task....
(Before I begin you need to know one size does not fit all as far as adapters go...get the adapters now..even if your just thinking of buying one of these tubes...just get them).
Headphones - Senheiser HD6XX & Fidelio X2
Tidal Playlist (Miles Davis-Radiohead-Bob Marley)
https://tidal.com/browse/playlist/b5ea485b-fdff-440a-944c-ca4ecca5f977
Tung Sol 7236 used for the push duties
Marconi 6CG7 1950's
History:
"In 1954, RCA came out with the 6CG7, which was pitched as a direct equivalent of the 6SN7GT. Although audiophiles found that the 6SN7GT typically sounded better, this was the beginning of the end for widespread usage of the 6SN7GT. The 6CG7 was unique in having a shield between the two sections". - effectrode.com
The 6CG7 caught my attention going through the Darkvoice Massdrop Forums, especially this post from user LIBY555
"Personally, I liked to use another different tube socket adapter and use a 6CG7. The 6CG7 has been called a 6SN7 in a 9 pin bottle. Electrically they are very, very similar but the 6CG7 does not sound like a 6SN7. The 6CG7 is brighter and faster sounding. Most of the 6CG7's are brighter sounding tubes, again, except for the RCA . You will find Sylvania, GE, Raytheon and even the occasional Tung Sol gray plate 6CG7. Depending on your ears all of them may be good for you. The RCA 6CG7 later became 6FQ7 and either will work ok but the RCA is richer sounding than the other 6CG7's but still brighter than most 6SN7's. I liked the 6CG7's a lot better most of the time.
The investment in a 6CG7 and adapter is much less than any good NOS 6SN7". - LIBY555
I grabbed a set of the RCA tubes for a side comparison to the Marconi, and yes as user LIBY555 described it the RCA sound fuller but I suspect only because the highs are not as extended as the Marconi, the RCA are without the shield between the plates so not sure how that effects sound just a note in build. These tubes do rival the nicer 6SN7GT out there and if on a budget, worth the collection.
(Kind Of Blue) Instruments are really life like here, I got front rows seats, no I'm sitting in the middle of this jam session. The double bass instrument just bellows beautifully. Smoked filled bar sipping on a beer kinda mood.
7N7 1950's (Philco, Sylvania)
History:
"Sylvania and Raytheon came out with a loctal version, called the 7N7, which, interestingly, was registered in 1940, well before the 6SN7GT. Primarily due to the non-acceptance by RCA (the Microsoft of its time), the loctal line, though technically superior to the octal types, withered away in the late 1940s". - Effectrode.com
They do make a strong case for sounding technically superior. These tubes can exude mad air of sound around you (especailly with the Fedelio X2), a very lively tube. And when you find a great jazz recording like Kind Of Blue by Miles Davis.... does it get any better?
The 7N7 is basically a 6SN7GT tube without the base, all the internals are the same (especailly/mostly with the short bottles). I don't see much or have yet to see a tall bottle 6SN7GT bottle that shares the same innards as the tall 7N7. The other differences would be the pin layout.
For the most part of the three 7N7 tubes I have (one short, two tall bottles) the tall bottles have the better imaging and overall stage presence. I do have to mention Headphoneus Supremus member bcowen has named a particular 7N7 tube, one that he states..
" I ran across an Ebay ad for the tall bottle pictured below. And the rest is now history. Powerful bass, dynamic and punchy, a midrange that's *just* right, beautiful treble, the rhythmic drive of a Foton. But there are two things that are remarkable with this tube: imaging (or maybe soundstaging) that locates each performer or instrument in its own acoustic space. You can pick out the individual voice in a chorus and the 3rd violin from center in an orchestra. And you hear the space surrounding them. I haven't heard this space-reality thing with headphones before". -bcowen
He's named this tall 7N7 tube "The FRANKENTUBE" and it's caught on by all headfi members following this guy. The one tube that will for sure qualify as The FRANKENTUBE is the JAN CBRZ 7N7 (Lansdale). These are super rare and hard to find. He does point out there are carbon copy builds with no notable differences in sound. (General Electric for example) again more from bcowen..
"The stuff required to be knighted as a Frankentube:
1) Tall bottle with unique 'squared-off' top shape.
2) Top getter with flashing that completely covers the inside of the bottle at least a 3rd of the way down, and usually half way down.
3) T-Plates where the flat part of the plates face each other. There are gray plate and black plate versions. I have both, and can't honestly tell much difference between them.
4) True racetrack mica supports, top and bottom. By that I mean that the shape is a true oval, and not like a rectangle with ends that are rounded (see below).
5) Square (or slightly rectangular) pan-type getter tray (or support)".
-bcowen
I can only imagine what a FRANKENTUBE would sound like as the tall tubes in my possession lack the very flat top tube appearance. As they are now, they sound incredible. Instrument separation above average, and lively.
Sylvania CF8G VT-99 1940's
History:
"The immediate predecessor of the 6SN7GT was the 6F8G, developed by RCA in 1937. The 6F8G was a dual version of the 6J5, which was a slightly “hotter” version of the 6C5 of 1935. The 6F8 had the larger “G” (or ST-12) bulb with the troublesome grid cap for one of the triodes. The compact straight-sided GT “Bantam” types, introduced by Hytron in 1938, had become the rage by the early 1940s, and the 6SN7GT was the natural evolution of the unwieldy 6F8G". - effectrode.com
The Sylvania VT-99 CF8G has a lush warm sound, with sweet reverb that seems to echo off walls of a concert hall. Laid back and smooth. As what you would expect from a tube made in the 40's, an 80 year old tube..let that sink in for a minute. Of the three this one will stand out the most as an interesting conversation piece, the small coke bottle and wired top cap design, you almost want to call this your end game tube and permanently leave it there. Because of the afore mentioned qualities I can forgive it's small short comings, it's not as dynamic or as fast as the 7N7 or 6CG7, but it doesn't need to be, it's perfect as it is, romantic and musical.
Note: This tube runs the coolest of the three
Tid Bits:
Kind Of Blue (by Miles Davis) if your into this album or new to it, I highly recommend Somethin' Else by Cannonball Adderley. If there's a resemblance in style it's because Cannonball left his group to help Miles Davis on the Kind Of Blue recording (the highest selling jazz album of all time), a year later Miles Davis returned the favor and helped him record Somethin' Else. both classics.
I've read that National Union has a grey glass bottle that's distinctly theirs. I also have a Tall Bottle that's Sylvania made. From the few articles I've read, Sylvania and RAytheon were the only one's making the 7N7 tubes for all other manufacturers. You got me really curious and now I'm searching the net furiously..lol, I'll update if I find any new news! EDIT: And yeah right away I just read from the Reference 6SN7 thread that it was RCA and Philco who created these. It's safe to say that Sylvania built the bulk of these 7N7 tubes for different companies.
Between $30 to $50, and if you look enough people who don't know what they have... $3 Tall Bottles are the one's you want, and her'es a pair, not matched. --> https://www.ebay.com/itm/7N7-loctal...=23322397756794bff175c57b4882a5831b8eedc92c9d
i accidentally ripped the cap off my Sylvania VT99 CF8G tube!! *&%*&^$% I'm glad I held my cool.. went to Home Depot and got the cheapest soldering iron there, took me a half hour to figure out how to fix the cap in place as these things get extremely hot! I almost gave up when I noticed a very small pinhole top of the cap, seated it on the thin wire it was attached too, and just placed the tip of the soldering iron at the top...and it held!! Who knows for how long.
I pulled on the cord instead of lifting it by the cap, which I usually do but in my haste.... yup..haste makes waste. I know little to zero about soldering, and did the YouTube video before attempting the reconstructive surgery.
The one video I saw did recommend the lead free rosin core. So wondering now that I've saved my beloved VT99 if I should try the Fitz Mod or just let things be...
There's an old saying: If it ain't broke, don't fix it.I pulled on the cord instead of lifting it by the cap, which I usually do but in my haste.... yup..haste makes waste. I know little to zero about soldering, and did the YouTube video before attempting the reconstructive surgery.
