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The 6DJ8, 6922, 7308 Saga - Part 1

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Posted on March 29, 1999 at 19:59:08
Joe S


 
Well this time I’ll be reviewing substitutes for the ubiquitous Sovtek 6922. That means it s time for 6DJ8s, 6922s, 7308s and a few other odds & sods thrown in for good measure. Once again all the usual caveats apply, so here we go!


Special warning to Audible Illusions preamp users

The one you can say for the Sovtek is that you can run it hard and it can take it - and apparently that’s exactly what AI does. Unfortunately the classic NOS tubes in this family just cant take this kind of treatment and will rapidly fail when used in these units (and some of you guys have the fried tubes to prove it!). So you AI users are probably best off limiting yourselves to the Sovtek, the Russian 6H23N & 6N1P, the 7DJ8 and the E288CC. There may be others – the range of tube types and variations is quite literally bewildering – but these are the ones I’m aware of that should be able to handle the higher stresses of this brand of preamps. I review the Edicron, Siemens E288CC and 6H23N here but there are other brands for some of these. I’ve seen Phillips E288CCs & Amperex 7DJ8s advertised on some web sites in the past and there are probably others. It might be worth your while chasing them down & evaluating them for yourself to increase the number of alternatives for use in your AI.


A Note on Numbers

The 6DJ8 family was originally developed by Amperex. The first tube in the family was the steel pinned 6DJ8 followed by the gold pinned 6922 and 7308. These latter two were premium versions rated as 10,000 hour life tubes. The 6922 was a premium industrial version and the 7308 was the top of the line guaranteed low noise version. Frankly, I’ve measured & listened to a lot of these and there is no correlation between model # and sound quality. Some of the best sounding tubes in this family are 6DJ8s and some of the worst are 6922s & 7308s. So take each tube on it’s own individual merits rather than judging it by its model number or pin material (gold pins do not necessarily = better sound). The Europeans used different model numbers to identify these tubes, by the way. In their numbering system the 6DJ8 was an ECC88, the 6922 was an E88CC and the 7308 was an E188CC. Oh, by the way, a 7DJ8 is basically a 6DJ8 with a 7 volt heater voltage rather than the 6DJ8’s 6 volt rating. What does 6H23N mean? Who the hell knows! I sure don’t.


Physical Structure:

The late 1950’s and early to mid ‘60s tubes in this family had a unique internal structure. Starting at the bottom of the tube and working our way up, first we find the wiring leading up from the pins to the tube’s internal structures. Next is the lower mica spacer – it’s a horizontal round disc of mica. This can be round with a serrated or scalloped edge (like a Siemens), or kind of a smooth edge disc with a slightly square shape with rounded corners (like on an Amperex or Sovtek). On top of this are the two vertically oriented plate structures. In this tube type the plates always seem to be painted grey. On top of the plates is the upper mica spacer – its just like the lower mica spacer. Up to this point I’ve just described 90% of the 9 pin miniature triodes in the world – it’s above this point that things differ. The next structure up is the unique one – it’s a horizontal, circular, metal disc supported by two metal bars. I’ve seen & heard this referred to as a “shield” or a “splatter shield”. Which name is correct & what is the purpose of this structure? I don’t know, but most all early 6DJ8 family tubes have it. Above this is the getter halo. The halo is usually a metal ring supported by a single metal bar. On some tubes, like very early Amperexes, the getter halo isn’t a ring but instead is a two part metal structure made from wire in the rough shape of the letter “D”. Tubes with this type getter halo are commonly referred to as “D getters”. Go figure.

You will often find a different internal structure in what are apparently late production 6DJ8 family tubes from the mid/late ‘60s through the ‘70s. These tubes sometimes had a simplified internal structure that eliminated the splatter shield / getter halo arrangement. In these tubes two metal bars angle up from the upper mica spacer, almost to a point, with a small metal disc on top. Viewed from the side this metal structure on top of the upper mica spacer looks a bit like the letter “A” – hence the nickname “A frame”. The other exceptions are some late Siemens 6922s & 7308s that just have a single metal rod rising above the upper mica spacer with a ring shaped getter halo on top – a practice copied in the Russian 6922s and 6H23Ns.


Das Toobs:

Enough prologue, on to the tubes! This time out I’m not going to group tubes by quality, instead I’ll take them one at a time by brand & give a brief capsule on each. It had been a while since I listened to some of these guys so I pulled & reviewed my old listening notes, reassembled all the tubes and spent an evening swapping and listening to each pair in my Thor DAC.

Sovtek 6922 (polished steel pins) – A bit sterile and lifeless, lacks a bit in dynamics, rolls the deep bass just a trifle and can occasionally sound a bit hollow in the mids. In short – Yawn...

Russian 6H23N (steel pins) – A Russian tube imported by the good folks at Lamm Audio. It came stock in my amps & is a slight improvement on the Sovtek. While basically similar to that tube, it has a bit more jump, slightly improved deep bass and slightly more palpable mids. The differences are not huge however, so whether or not its worth it to you is an individual decision....

Edicron 7DJ8 (with shield, steel pins) – A bit livelier NOS kind of sound than either of the above tubes. A little thin though compared to my favorite Amperexes & Siemens. While this tube represents an improvement over current production tubes I couldn’t live with it (but then I don’t use and AI preamp, so I can run any 6DJ8 I want without worrying about tube life – sorry guys!) Ultimately, if I were limited to the first three tubes, this would be my choice.... Also, the source of this tube is a bit questionable. See the Valvo 6DJ8 below for more comments.

Siemens E288CC (with shield, gold pins) – More transparent & dimensional with better bass than the Edicron. Also has more palpable vocals and a more lively, real sounding presentation than any of the above. But it’s not even close to Siemens best in this family. Expensive and hard to find too. But the best so far....

Siemens 6922 / E88CC (with shield, gold pins) – Now things are getting more interesting. It’s lively, has a palpable & real quality to individual performers with greater dimensionality than any of the above tubes. Warm, lively & transparent with an extended high end. This is a classic tube and an excellent choice in this family if your system is not already over the top in the high frequencies. Often found labeled as a “made in West Germany” RCA for as little as $20 a pop. An absolute bargain....

Siemens 6922 / E88CC, RCA label (A frame, gold pins) – This tube is similar to the earlier 6922 above. Vocals are slightly bigger and slightly more forward, the highs are a bit softer and the overall sound of the tube is a bit warmer. Music is presented with a warm, vibrant acoustic. Very nice & musical, though it might be a bit dull in a system that’s already dark in balance. Another excellent tube...

Siemens 6DJ8 / ECC88, RCA label (with shield, steel pins) – Kind of lives in between the two 6922s above. Warm & vibrant, with a slightly forward balance similar to the A frame. Slightly more extended highs than that tube, however. Another very nice tube, frequently found labeled as a “made in West Germany” RCA....

Siemens CCA (with shield, gold pins) – This tube is a premium version of the 6922. It is also one of rarest & most sought after tubes in this family and is priced accordingly when you can find it (not often). Slightly more dimensional, transparent & focused sounding that the Siemens 6DJ8 and 6922s above. It lacks a bit in bass punch compared to those tubes however and is slightly dry sounding in comparison. In short – maybe better in some ways, but not a reason for living. In other words, if you are stuck with living with the lesser Siemens tubes don’t worry about what you are missing....

Siemens 7308 / E188CC, RCA label (with shield, gold pins) - Sacrilegious comment time. I prefer the slightly warmer, more vibrant and wetter sound of this tube to the sound of the CCa. Closest sound among the Siemens line to the sound of my favorite Amprerexes (coming up soon!)

Siemens 7308 / E188CC, Phillips SQ label (no shield, with getter halo) – Warm & transparent. Very close to the shield version above in overall sound quality. Another excellent tube...

Telefunken 6922 / E88CC (with shield, diamond bottom, gold pins) – Slightly hollow mids, not as rich as the best Siemens and Amperex. A bit like the Siemens E288CC, though a bit better than that tube. A good tube, but the more common & cheaper Siemens 6922s are much better choices IMO. (Absolutely pounds the Russian tubes, though!)

Sylvania 7308, RCA label (with shield, steel pins) – Vocals are sharper & less refined than Siemens, Amperex and the Teles. Not at all a bad tube & better than the Russians in some ways. Lively, vibrant, forward & good bass if a bit of an edge and a little brash. Not a great tube, but a good tube for the price. If your system needs some energy and high frequency oomph and you don’t have much cash this tube is a best buy....

Sylvania 7308, Siemens counterfeit (with shield, gold pins) – The morons who did this relabeled counterfeit of a Siemens didn’t even bother to rub off the original made in USA label. An object lesson for care in chasing desirable tubes, there are a lot of fakes and relabels of tubes like the Siemens 7308 and CCa based on the Sylvania & even the Tungsram. I’ll give some hints on how to avoid getting ripped off later in part 2 of this review. This tube is not quite as sharp as the above steel pinned version, but it is still a bit forward. Frankly I prefer the steel pin - this one is missing just a touch of that ones life...

Valvo 6DJ8 / ECC88 (with shield, steel pins) – Slightly thin sounding vocals with more air than body. Soft bass, sounds a bit like the Edicron 7DJ8 and that shouldn’t be a surprise – this tubes internal construction is identical to that tube (at least on my pair, anyway). These tubes were obviously made at the same plant. In fact, close inspection reveals that every aspect of this tubes physical construction is absolutely identical to the Edicron down to the fat, round top, Russian style bottle and the bright red color on the pins where they pass through the glass. In fact the bottles on both tubes are identical to the Sovtek 6922 – so these tubes were either made in Russia or they were made in an Eastern Block country equipped with Russian tooling. Edicron labels their boxes “London” but that ain’t where either of these came from....

Raytheon 7308 (with shield, steel pins) – OK mids, soft on top, good bass. Better than the Russians, but not by tons. As good as the Sylvania 7308 steel pins, but in a different sort of way. Not a great tube, but a good one...

Ediswan CV 5358 (splatter shield, steel pins) – Good, palpable vocals, nice upper & mid bass with a nice sense of impact in that region. Good if slightly soft highs. This tube is almost in the same class with the Siemens gold pins if just a bit softer in balance on top...

Whew! Its getting late and I’ve got another dozen tubes to review (including a pile of Amperexes!), some pointers on how to identify the real thing in order to avoid to get ripped off, and a few observations on OEM branding and how that can save you some money – In other words way to much to cover now. So until tomorrow night and part 2, good night and good listening….

Stay tuned,

Joe



 

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    ...
You are thorough, posted on March 30, 1999 at 06:44:57
Jack G


 
If only you'ld review 2A3s and 6SN7s etc.
Sometimes its a pain in the butt not having anyone to do the homework for you. Ah, its the price for marching to a different drummer.
Jack

 

Thanks Joe, your FAQ has been updated (nt), posted on March 30, 1999 at 07:45:26
Rod M


 
.

 

If we ever meet, I'm buying!, posted on March 30, 1999 at 11:36:13
Edp


 
Your hard/long work at posting these is shown in the output. These posts have helped me greatly. I appreciate the effort, and will pay you back in either person, or through kharma, passing on what little I know to others.

Thanks.

 

Re: The 6DJ8, 6922, 7308 Saga - Part 1, posted on March 30, 1999 at 12:06:20
Keith F


 
Can the above mentioned tubes be used in a Audio Research LS15? I would love to experiment but was told by dealer they only take 6922's.
Keith

 

Yes (nt), posted on March 30, 1999 at 12:27:05
Jack G


 
Ò¿Ò

 

When you're in SF next..., posted on March 30, 1999 at 13:54:50
SFDude


 
...let me have the privelege and honor of treating you to a nice San Franciscan restaurant. DAMN you're detailed, thorough in your observations and have VALUABLE data for all of us to use in our hunt through various tubes to use in our equipment. And I couldn't thank you enough as your postings have helped me enormously in fleshing out what's worth looking for and what's not.

E-mail me anytime when you're in town...and THANKS!!!

(Hunting down more NOS tubes...I'm checking other sources now...)

 

Thanks Joe, excellent report. (nt), posted on March 30, 1999 at 15:27:02
Jerry P


 
nt

 

Did you...., posted on March 30, 1999 at 16:32:17
Bryan F.


 
....burn/run each tube in? As even tubes need to be run in. 6922's don't usually come to life until 80-150 hours.

Also the Audible Illusions 3A is hard on tubes for two reasons. One it is a very high gain preamp and two it uses zero negative feedback if memory serves me right. For these two reasons it eats 6922's.

 

Re: Did you...., posted on March 30, 1999 at 19:47:11
Joe S


 
Yes all tubes have been burned in. But frankly I have found few 9 pin miniature triodes that have changed significantly in sound quality past the first few hours (in many cases literally the first few minutes). Ceratainly they do not exhibit the recalcitrant burn in characteristics of the typical audiophile capacitor for example... ;-)

Joe

 

I had to ask!...., posted on March 30, 1999 at 20:10:30
Bryan F.


 
....as I have noted a few differences though it takes many hours. If you want to see what I am talking about buy two sets. Let one set run in and test it against a set that isn't. I know I have been surprised. Tubes are funny in that they begin life in an infant stage and then blossom only to become old and worn.....great post.

 

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