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12AX7s - Part 1
12AX7s - Part 2
12AX7s (5751s) - Part 3
The 6DJ8, 6922, 7308 Saga - Part 1
The 6DJ8, 6922, 7308 saga - Part 2

Life with 12AU7s....

Posted by Joe S on March 04, 1999 at 16:04:14:

Here's an edited version of an e-mail I sent EDP regarding 12AU7 experiences in his time of need. I make no representation as to how any of these tubes might sound in your system, but it might help narrow down to a few choices for an evaluation of your own.

Without further ado, here we go....

Now, regarding tubes, yes those 12AU7s in your amp are indeed drivers, and no, if you change them it will not effect the bias of the output tubes so experiment as much as you want. I've posted on AR a few times on this tube type, but I'll go into a bit more depth here. I've been through the mill on this tube type over the past year and tried the following tube types:

  • RCA 1960s top getters gray plates
  • RCA 50's top getters black plates
  • RCA '60s clear tops
  • RCA black plate 5814As
  • GE grey plates
  • Sylvania grey plates
  • Sylvania '50s black plates
  • Sylvania '50s limited production black plates
  • RFT (German)
  • Valvo
  • Mullard ribbed plate
  • Mullard box plate CV4003
  • Brimar
  • Amperex Holland Orange globe logos
  • Amperex Holland Bugleboys
  • Amperex Holland 7316 (instrument grade)
  • Tesla
  • Telefunken smooth plate
  • Phillips
  • Tung Sol 6189 / 12AU7WA
  • Raytheon

    Now frankly, most of these are competent at best and not really anything special - in fact I would say this is a fairly unexceptional tube family with just a few high points. In my system the only tubes of merit broke out something like this:

    Best of the lot

  • Amperex Bugleboy 12AU7 Holland
  • Amperex 12AU7 Holland (no bugleboy logo, later production)
  • RCA Clear top (side getter) 12AU7
  • RFT 12AU7

    Best of the rest:

  • Mullard CV4003 box plate

    That's it. The rest, amazingly enough, weren't worth the waste of time in my rig - but the risk of course is that one of those might ideally match your rig, 'cause with tubes you never know what's going to lock-in in any given system. Given that, the 3 tubes I identified as the winners do have fairly broad followings among audiophiles while most of the others do not, though a few do like the Mullard box plate.

    When it comes to sonics general comments go something like this:

    RFTs - linear, clean but just a bit clinical and hard sounding. Good transparency and detail.

    RCA - A bit fuller, richer and a bit more vibrant than the RFTs, not clinical, but still good detail. A more traditional NOS sound.

    Amperex - I think the bugleboys are a bit better,but I might be fooling myself, so these comments apply to any Holland made Amperex 12AU7. Full range, nice extension on top with a great sense of vibrancy, transparency and life with very good focus. This tube sounds warm, vibrant, exciting, extended & clean on top, yet smooth and fatigue free all at the same time. Clear winner in my system.

    Oh yeah, the Mullard Box plate - Nice extension on top, tends to emphasize air and ambience at the expense of just a bit of focus, but still nice overall. Just not quite as good as the three above.

    Now of course the above might not translate to your system but if I were going to do some experimentation I think I'd chase down a pair of RCA clear tops first. These things are common as can be, cheap (if you pay over $12 a piece you're paying too much) and sound ridiculously good for the money. You will see these at a lot of hamfests and amateur radio shows, often for as little as $5 - $8 each. If those didn't work out and I needed a more controlled and solid state kind of character I'd then go hunt down some RFTs. You wont find these at the average hamfest - more likely, you will have to mail order them from an NOS dealer. Typical price is around $15 to $18 each. I've seen them at Triode Electronics in Chicago, and a few other dealers sell 'em too. The Tech Talk (now that dates this e-mail doesn't it? - Sorry!!)crowd could help there. If, on the other hand, after the RCA experiment I liked what I heard then I might then spring for the Amperexes. They take the basic RCA clear top sound to another level entirely, thought the degree to which they sound better is a bit system dependent. At least one TT poster thinks they are better, but not worth the extra scratch - I find them indispensable and a rather dramatic improvement. Then again my system is very transparent & I'm pretty anal when it comes to the sound I like. Problem with these guys for some is cost. If $35 to $40 a tube doesn't phase you then it's no big deal, but if you don't like the idea of spending that much then there is you're rate limiter, because they are desirable and priced accordingly. You wont see these too often at hamfests even though there were a ton of them made - audiophiles have been snapping 'em em for years and they are getting scarce & expensive. Oh, and by the way, stick with Holland made tubes for these - Amperexes are labeled by country of manufacture and the Hollands are clearly the best.

    So, hopefully that gives you a few pointers and some ideas. Oh, well that's about it for now, so good luck and be sure and let me know what you find!


    Now shifting back to the present, the only other comments I might add relate to the obvious "what about the Mullard rib plates & legendary Telefunkens?" question. Well frankly there wasn't much to say. IMHO these are two of the most overrated brands in the NOS universe. generally speaking all the Telefunken 12A family tubes I've heard ('X7s, 'T7s, 'U7s) are a bit bright, thin and airy sounding. I've talked to Charlie Kittleson at Vacuum Tube Valley about this and he basically agreed, observing that these guys more or less built their reputation on their use by the old gear crowd. Why? Well his comment was that the caps, resistors & transformers in old gear were dark sounding sludge and the Teles offered a useful brightening of the sound to a more natural balance. The issue, of course, is that when you put them in a contemporary design with much wider bandwidth and a more neutral '90s kind of balance things can go over the top.

    Now before any Tele lovers who find them ideal in their new gear freak out and tell me how wonderful they sound - I believe it. There is a system out there somewhere that's the ideal match for any tube. This is just a comment on a general tendency. Now Mullards are another matter. I have found a few that sound quite nice and they generally are warmer than Teles, but in my rig they never quite make it to the top of the heap.

    Life with 12AX7s - Part 1

    Posted by Joe S on March 17, 1999 at 19:05:44:

    Well, here's the promised second installment of my tube odyssey into the world of small signal NOS tubes. Just to get the formalities out of the way here first - Yes NOS tubes do sound different from current production tubes. Yes they will have real impact on the sound of your system. And yes, they all sound different. Which will sound best in your rig? Who knows. There are significant differences in the way in which individual components, systems and tastes interact with individual tubes so my experience may not predict yours, in other words - "Your mileage may vary" - but hopefully this may help separate some of the gems from the dregs for your own personal evaluation short list....

    Well, first things first. This is the ubiquitous small signal triode, they are probably about as commonly used as 6DJ8/6922s and in my humble opinion they are widely misunderstood. Why? Because the hype surrounding a few specific supposedly invincible NOS brands is way out of proportion to their true quality and their likelihood to mesh with any given system - but more on that later. My opinions are based on using this type in my system in 4 different preamps over the years - most recently in the output stage of the Thor.

    Now on to the tubes themselves. Brands and versions I have on hand include:

  • Sovtek 12AX7 WXTP(premium, supposedly modeled after the classic Telefunken)
  • Telefunken 12AX7 ribbed plates
  • Mullard 12AX7
  • Mullard CV 4004 box plate
  • Sylvania (Phillips) JAN 12AX7WA
  • Brimar CV 4004
  • RCA 12AX7A grey ribbed plate
  • Amperex 12AX7 Bugle Boy Holland

    I've also owned and heard the GEs in the past but thankfully don't have a pair on hand at the moment ;-) Now, regarding nomenclature - the CV numbered tubes are British military tubes labeled according to the British Military numbering system - they are still just 12AX7s. The WA on the Phillips denotes a premium or select version.

    Now when it comes to sound quality where do I begin? Well, to my ears - they ALL suck. There, I said it. Even (particularly?) the legendary Telefunkens. How can this be? Well, every 12AX7 I've ever heard has a common sonic character that's drives me to distraction. Specifically, they all sound a bit fuzzy, unfocused and hazy with a subtle sense of a soft sonic haze permeating a soundstage populated with large unfocused images. Added to this are other sonic artifacts unique to each tube. To hit a few of the highlights, here goes:

    Telefunken 12AX7 ribbed plates - a typical soft, unfocused 12AX7 sound with big, soft, images allied with a bright bass shy character. I was shocked when I heard these guys first hand, but the more I talked to people who knew these tubes the better I understood them. I generally associate NOS tubes with a warmer, more harmonically complex & rich sound than current production, but light and airy is the order of the day here - to the pint of brightness. The secret is that these guys are a favorite for use in a lot of old classic gear from the '50s & '60s where the transformers, wire and caps used were thick, dull sounding sonic sludge. The bright balance of this tube is great complement for this kind of gear, but drop it into current broad bandwidth tube gear (like the Thor) and you might just get sonic hell - all for just $50 to $65 a tube!

    Mullard 12AX7 ribbed plate - a warmer and fuller sound than the Tele, but it still suffers from the typical 12AX7 softness and lack of focus. A bit rolled at the extremes in my rig and more forgiving than the Tele. All in all a better choice for contemporary gear in most circumstances IMO than that tube - but I'm still not getting any shin burns from my sox rolling up and down in excitement at the prospect...

    Mullard CV4004 box plate - very extended at the extremes, great frequency response overall in fact, but maybe even more fuzzy than the usual 12AX7.

    Amperex 12AX7 - now this one is a bit more interesting. The typically vibrant yet rich and transparent Amperex sound with less of the typical 12AX7 softness and lack of focus. If I lived in a world in which I had to use a 12AX7 this would be the one I would use. But I don't & neither do you, but more on that later...

    The rest of the pack - the Sylvania/ Phillips, GE, RCAs, etc.. are even worse. In fact, added to the usual (to my ears) 12AX7 sins add lack of refinement, microphonics and huge sample to sample variability. Not a pretty sight, trust me. And, oh yeah - the Sovtek? Its a cool harmonically bleached and basically disappointing beast that I wouldn't use under any circumstance - but hey, that's just my opinion.

    Well I've just run roughshod over some of the most revered tubes in the NOS universe and basically damned them with faint praise at best. So what do you do if your gear has a couple of sockets that expect to see a 12AX7? Well I would propose that you cast an eye toward the 12AX7s more refined and altogether superior offspring - the cheap, lowly 5751. In its day (it was introduced in the mid '50s) the 5751 was created as premium 12AX7 designed by US manufacturers to overcome the well known limitations of American made 12AX7s, specifically: huge sample to sample variability, microphonics and noise. The fact is this tube had considerable care exercised in its design that is evidenced in its physical construction: Rigid metal rods linking the mica spacers for a more rigid less microphonic tube, a third mica spacer to brace the getter halo (again to combat microphonics), careful testing to assure consistency tube to tube and lower mu (apparently to combat noise) which results in an altogether more focused & palpable sound.

    But then a funny thing happened. This tube was made in massive quantities by companies like Sylvania, RCA, GE and Raytheon and was supplied to the US military resulting in massive JAN stocks of NOS tubes lying about. Just not the sort of exclusive limited availability tube that exclusive NOS tube dealers could charge $ 50 a pop for - like those rare & exclusive Tele & Mullard 12AX7s...So a premium tube with great performance and a genuinely careful design has knocked about as a common $8 NOS plug in for 12AX7s while its less capable but better known 12AX7 competitors have achieved legend status. Now all may not be well in audio land here so I'll warn you now. The 5751 has a lower mu than a 12AX7 and some circuits purportedly don't abide by that but I've tried them in 4 preamps with no problems and this guy has found pride of place in a lot of tube preamps over the years CJ used them in their line stages for years and Joule Elektra ran them in the LA 100 / 200 series of preamps until very recently - so there are other people have heard the merit in these guys too.

    So if the 5751 is the direction to look, where do you start? Well there are several choices and vintages (most of which are ridiculously cheap) that will put a Tele or Mullard 12AX7 to shame - but its late & that's a story for part 2 of the 12AX7 story....

    Stay tuned,


    Life with 12AX7s - Part 2

    Posted by Joe S on March 22, 1999 at 08:42:13:

    Well here's the other half of my personal journey into the world of 12AX7s. Again all the usual caveats apply, these observations are based on the sound of these tubes in my rig, in my room within the context of my taste. While I think these comments are somewhat generalizable the fact remains that given the variability of gear out there every tube has an ideal match out there somewhere so if I don't get excited about it that doesn't mean its a lousy tube - it just doesn't work as well in my rig as some of the others. Given that here we go.

    Well, I tend to break the 5751 family of tubes into two groups in terms of sonic quality and capability. This is a bit arbitrary but it reflects my own preferences and experiences and the fact that I do find significant differences in sound quality among these beasts. The first group are the tubes that I find a bit less exceptional for various reasons - note that I'm not calling them bad tubes. In fact I find any of these superior to all 12AX7s (except perhaps for the Amperex) so they are in fact a great place to start your 5751 odyssey. There are other reasons you may want to start with these tubes as well, but more on that later. In this first group I would include the following:

  • GE grey plate
  • Sylvania grey plate
  • RCA black plate (common??? version)
  • RCA black plate (silver clip??? version)
  • Siemens grey plate

    Now a few general comments regarding these guys before I get a bit more specific. All of these tubes have a more focused and transparent sound than 12AX7s with less fuzz & grain and a greater sense of palpability (sorry about that, but its the only word that fits for me, Jack G would say organic here, I think) which is particularly noticeable on vocals. When it comes to the way they present individual performers what you will hear from these guys a is a focused dimensional object rather than a flat cardboard cut out or fuzzy undefined image. This allied with the lack of the typical 12AX7 fuzz results in a more clear, open sound with good transparency and detail. I also hear a greater sense of layering in the soundstage with these guys than with 12AX7s. 5751s also tend to be warmer & smoother than some of the 12AX7s, in fact a few of these guys sound downright sweet in comparison. These traits are endemic to the type in my experience, but there are still significant differences tube to tube. Now, taken individually I hear something like this:

    GE grey plate - 3 mica spacer version: A bit less refined than other 5751s, this is the entry level tube of this type. If you've ever heard the linestage of a CJ preamp made in the 1980s you've heard this tube since that's what CJ used in the line section of all their preamps for years. This tube can sound a little brash at times and is a bit less liquid than some of the others but its still a good tube. Common as water too, huge JAN stocks of this guy abound so he's cheap & readily available - typically $8 to $12 a tube. If you are messing with 5751s its worth grabbing a pair of these...

    Sylvania grey plate - 3 mica spacer version: A bit more refined and grainless than the GE. Actually a pretty nice tube that was used in series the RCA black plate in the Joule Elektra LA 100 & 200 series preamps up through the mk 2 units. A little bit forward in balance in my experience as are all of the Sylvanias in this type (oh yeah, the best in this brand & family is yet to come! patience, patience...) Another JAN tube that's common & cheap. Once again if dabbling in 5751s, one I would put on my short list and definitely nab a pair of...

    RCA black plate (common??? version) - 3 mica spacer version: OK controversy time. Common wisdom among 5751'o'philes is that this tube is the cats meow, the one to own, the audiophile's dream, the...uh, you get the point. But the odd thing is I have found multiple versions of this guy that vary rather dramatically in sound quality. I am using my own nomenclature here calling this the common version - I've seen this style more often than the others and is the type I've bought from 2 national tube dealers. The way to distinguish it from what's to follow is to look at the top and bottom corners of the black plates themselves where they protrude through the upper & lower mica spacers. If all you see are the corners of the plates themselves, or at most small silver rectangular tabs attached to the tips of the plates, its the type I'm referring to. Sound with this guy is quite good. He's smooth, warm, linear and sweet on top. If your system is bright and brash and needs a warming influence this guy could be the ticket, but still not in the league with the best of this type in my (not in the least bit humble) opinion. Another common tube, but it's audiophile reputation precedes it so it will typically set you back $12 to $18 or so - still cheap as dirt compared to those premium 12AX7s.

    RCA black plate (silver clip??? version) - 3 mica spacer version: Talk about another kettle of fish. This tube is as different from the RCA above as any other tube of this type. Irony is I've NEVER seen any tube dealer distinguish between the two. To be fair, as near as I can tell, this guy is quite rare and I have only seen it (and bought it) at two hamfests. While the tube looks very similar to the description above it is distinguished by what I call silver clips. You will see these on the tips of the plates where they pass through the upper and lower mica spacers. That means there are 4 on top of the upper mica spacer and four below the bottom mica spacer, and you can't miss them - they are utterly unique in my experience and appear designed to clamp the entire plate / spacer assembly together (presumably to combat microphonics). These clips are chrome silver, about 1/5 of an inch long and wavy in shape - in short, they are big & obvious enough you can see them at a distance of 3 feet. Now, the sound. These guy is a very transparent and broad band tube, particularly extended on the high end with a very clear and open presentation. It also might just have the best soundstage of any 5751. The only downside? It can be a bit bright & relentless, I would only mate this with a dull, warm system that needs some spicing up. In my rig it sounds dazzling, but ultimately fatiguing. I don't know what to say about availability - the clip description is my own, I don't know of any NOS dealer who would know what you were talking about if you asked for it. Oh yeah I've found it in '50s RCA markings and in late 60's RCA new red logo livery, so I cant even comment on vintage. Oh yeah, when I have found it at hamfests, its relatively cheap - $6 to $12 a pop.

    Siemens grey plate - 3 mica spacer version: Well I love Siemens 6922s, 7308s and even their 6DJ8s, but this is one tube I found a bit disappointing. Overall it is very linear, neutral almost to a fault and ultimately a bit sterile sounding. In my rig you could almost mistake this for a current manufacture tube. Somehow it just lacks a bit of that NOS magic that makes old tubes so fun - but then again if you have an overly romantic sounding system it might find a useful home in your rig. This tube tends to command premium prices ($20 and up) due to its lineage, but in my not so humble opinion it ain't worth it.

    Now that's it for the more commonly available tubes in this family. I would however, like to address a few issues that arise relative to these guys as well as a few other brands that are actually nothing more than reliable of the above tubes before moving on to the esoterica.

    First off - regarding 2 and 3 mica spacer tubes. The 5751 was somewhat unique in that its design originally added a third mica spacer (the round, usually serrated edge horizontal discs above and below the plates) above the upper mica spacer. In fact, every 1950's production tube of this type I've ever found has this upper disc which clamped the getter halo in place, apparently to combat microphonics. These early tubes invariable possess two metal strengthening rods between the plates which also helped lock the whole plate / spacer assembly together. But towards the end of the tube era that all changed. I've seen RCAs, Sylvanias and GEs from the mid to late '60s and '70s that have only two mica spacers and no strengthening rods - apparently casualties of cost cutting towards the end of the tube era. And it gets worse. I've measured quite a few 5751s for noise, gain & microphonics and I've always been struck buy how consistent, quiet and low in microphonics they are - the 3 mica spacer versions that is. The 2 spacer versions? Forget it. All over the map, noisy as hell, terrible for microphonics. Now I'm sure there are good 2 spacer tubes out there but the point is that while I would buy earlier 3 spacer tubes unmatched and untested, I wouldn't buy the 2 spacer versions that way - based on what I've measured & heard I just wouldn't trust them.

    Now what about other brands? You will often see Motorola 5751s listed by some dealers. Should you buy them? Only if you need a pair of GEs and they cost no more than the GEs do, because that's what they are. Motorola never made them, they were OEM sourced tubes.

    The same is true of another, more legendary brand - Amperex. Wow, could you imagine a 5751 made by this legendary company? It would have to be the best of all worlds and they are sold on ebay all the time... Well imagination is all you've got here, along with a common old GE that is. Unfortunately Amperex never made 5751s so we will never know what that tube would have sounded like - instead Amperex sourced them from GE and the sound is the same as a GE labeled tube - oh well, what might have been....Oh, and by the way, you will never see a Mullard, Brimar or Telefunken 5751 because they never made them. This tube was the domain of US manufacturers and the Siemens is the only non US brand I am aware of in this type.

    Well, that's it for the more commonly available 5751s. Geez, this post is getting long & I haven't even touched on the second group of generally (but not always) rarer and even more desirable brands & types. I think that will have to be a story for part 3 of the 12AX7 odyssey which I will try to post before the day is out.

    Please bear with me...


    Life with 12AX7s (5751s) - Part 3

    Posted by Joe S on March 23, 1999 at 09:15:04:

    OK, so lets put this puppy to bed. This installment of the 12AX7 odyssey deals with the 2nd group of 5751s I mentioned in part two. This group reflects my choice of the best of the best. As with most all good things in life prices go up with quality and that is reflected in these tubes as well -with a few happy exceptions. Actually these guys are still typically cheaper than the premium 12AX7s - the issue with them is more one of availability. I've actually found some of these guys (the Sylvania Gold Brands for instance) at some of the premium NOS tube dealers for half the price of a Tele or Mullard 'AX7, when they have them. Its just they usually don't have them. Given that lets have a look at the cream of the 5751 crop....

    Well the tubes in my best of the best short list include the following:

  • GE black plate (definitely not to be confused with the grey plate version)
  • Tung Sol
  • Raytheon
  • Sylvania black plate government contract gold labels (JHS, CAA, etc..)
  • Sylvania Gold Brand black plate
  • Sylvania Gold Brand grey plate - gold pin

    Note that all of the tubes above have the 3 mica spacer design with one exception - the Tung Sol.

    Wow never thought I'd see so many Sylvania tubes on a bet of list in my life. While I generally find Sylvanias unexceptional in most all types in this category they are over achievers and that reputation precedes them. But I me getting ahead of myself. Lets start instead with the:

    GE 5751-WA Black Plate - This is a '50s production tube. Many tube freaks say its simply a relabeled RCA, but I own RCAs and there are subtle internal differences and rather dramatic sonic differences compared to that brand. This tube is often found as a military boxed government contract tube (ex.:JG-5751) and is always in my experience boxed in a white date coded box. They invariably have production dates in the 1956-1959, or so, range. Its got shiny black plates which are shaped differently from the later GE grey plate versions of this tube. OK, enough physical description, how does it sound? Well to my ears its a more refined and yet more lively tube than those in group one. It has a good linear frequency response with fairly good HF extension, if not quite as palpable in the mids as a few others in group 2, but not by much. It measures like a dream too. Like all early 5751s I've ever tested (1955-1965, or so) these guys are unbelievable tight in terms of gain, low noise levels and vanishingly low microphonics. I can literally grab any two of these off the shelf randomly and have a near perfectly matched pair - not at all typical of later production GE tubes. You will occasionally stumble on these at tube dealers and when you do they wont cost much, usually just $10 to $18 a tube - Why? No one seems to know about these guys. I've only found 1 NOS tube dealer whose ever listened to it and who understands how good it is. The others will sell it off like almost any other GE 5751 without realizing what they've got on their hands (heh, heh)...

    Tung Sol 5751 - this guy is a bit of a sleeper and odd man out here, but its worth grabbing if you stumble on it cheap. This tube is a bit different from the others on the list in terms of physical design. All of the other tubes here are of the 3 mica spacer design with short wide plates. This tube, on the other hand, has an internal construction similar to a traditional 12AX7 -tall ribbed grey plates with no 3rd mica spacer. Perhaps as a result of this it sounds a bit like a cross between the two types - while it is not quite as focused as the other top of the heap 5751s, it does have avery good sense of life, body and ambience. I actually lived quite happily with this tube in the Thor for about 4 months before stumbling on the next tube on the list. Pricing on this guy when you can find him is quite reasonable - usually no more than $15 a tube. You just wont see him real often, though I have noted a few ebay auctions recently and SND tube sales has had them in the past (sorry, I already cleaned them out though!)

    Raytheon - Well this guy is one of the happy surprises on the list. I first stumbled on him about a year ago and lived quite happily with a pair in the Thor until I finally found some of the killer Sylvanias. The great thing about this tube beyond its sound quality is its availability, but more on that later. The strength of this tube is its overall balance. Its got the 5751 sense of focus in spades, is clean, open and evenhanded in frequency response if just a little sweet on top. As a result it has just a bit less life and energy than some of the premium Sylvanias and even the GE black plate. Its also a bit less forward in terms of where it puts the performers in the soundstage compared to those tubes - but I still wouldn't call it laid back. Availability on this guy is pretty good. Tube world has been selling these for the past several months, SND has had them in the past as well, and a pair or two are on auction at ebay every few weeks. Price? Usually $15 to $18 a tube. I'd definitely track down a pair of these if I were playing around with 5751s...

    Sylvania black plate government contract gold labels (JHS, CAA, etc...)
    Sylvania Gold Brand black plate

    - Iím combining these, because my eyes and ears tell me they are indeed the same tubes. These are early Sylvania 5751s from the '50s and they are distinguished from their later brethren by their black plates. The Gold Brand (literally, Sylvania's premium consumer tube line) version is a bit unusual in that the black plate gold brands had steel pins rather than the gold pins of other tubes in that line. Both of these tubes were apparently made on the same production line - those intended for the consumer market got the Gold Brand label and those for government contract were custom labeled for the acquiring agency (JHS or CAA for example - CAA-5751, JHS-5751). The ink used on the tubes themselves was gold and it rubs off easily, so even NOS tubes can have partial labels. Now all of this is my conjecture based on comparing the internal structures carefully and comparative listening - but after doing so I am convinced the tubes are identical. So what do you hear when these guys are in circuit? Well they have an absolutely glorious midrange - female vocals are to die for, or is it kill for? (Don't get between me and the VR6s while these are in circuit and Iím playing Jonathan Brooke's Live cd - you have been warned!). The other thing is that they have a marvelous sense of life and a tangible (almost spooky) sense of 3 dimensionality to images in the soundstage, particularly vocals. The overall effect is one of a very transparent, warm yet lively sound with a complete lack of fizz or grain and a high level of detail retrieval allied with great vocal reproduction. Downsides - they are a bit forward in balance. If your system already pushes vocalists at you these guys might put them in your lap. But given that caveat I haven't heard a better 5751 in my system and I use it full time in my rig. Oh yeah, one other potential warning - one dealer who knows these well has experienced short tube life with the Sylvania black plates. I have recently checked my first pair after about 6 months of use and while one tests as new, the other tests as about 50% - so there may be something to this issue. I will keep you posted. Availability is the other problem with these guys. I've tracked down a dozen or so over the past year, but only one pair came form an audio NOS tube dealer, the others have been hard won through hamfests, reaching out to off the beaten path dealers and e-mail contacts. When you find them prices vary quite a bit - I've found gold brands for $25 to $35 and the govt contract JHS & CAA tubes for as little as $12 - apparently I'm the only human on earth who has gotten both and figured out that they are identical. And now you know too!!

    Sylvania Gold Brand grey pl ate gold pin - OK, this is the legend. When people talk wantonly about the famous Sylvania Gold Brand 5751 gold pins this is the tube they are referring to. Does it measure up to the hype? Well by and large, yes. To my ears it is the the 2nd or 3rd best 5751 ranking up there with the Sylvania & GE black plates. Its strength is its midrange, but it may also be its weakness. The mids here are full, lush, tangible and maybe (just maybe) a trifle overblown. Occasionally i find the lush full vocals obscure just a bit of detail and reduce transparency slightly, but the mids are so lush I could understand how you might not care. The tube also has a measure of life and vibrancy, similar to the Sylvania's black plates and it also has a bit of the forwardness that's seems to be endemic to Sylvanias in the 5751 family. I've lived with this tube enough to know I could use it quite happily, though that would be in the context of a fairly neutral system where its own colorations would not go over the top. If your rig is already warm, smooth, lush and a bit lacking in detail this guy could turn things just a touch syrupy. But given the sound of a lot of cd based systems he could be just the ticket... Availability on this guy is limited. His reputation has made him a rare, if not outrageously expensive beast (usually $30 - $40 a tube) and he is long lived, unlike his black plate brother. Vintage Tube Services has got these on hand every so often and you will occasionally find them at other premium audio NOS tube dealers. As with other rare beasts I've had more luck finding them at hamfests and through the dealers I've met at them, as well as by reaching off the beaten path to ham radio tube dealers and other tube sellers who don't cater to the audiophile crowd.

    Well there you go. One audionuts personal journey deep into the world of 12AX7s and their substitutes. What would I do if I were looking to test the 5751 waters? Well I'd look to assemble a cast of three or four alternatives for a personal in-home shoot out. The beauty of the 5751s relatively lower popularity and awareness compared to 12AX7s is that they are cheap. Your can buy 2 or 3 pair of these guys for the price of one pair of Teles or Mullards. A great place to start would be to chase down the more common versions, say a pair each of the Sylvania grey plates, Raytheons and the common RCAs - I'd only buy the triple mica spacer versions by the way. That pile of tubes would set you back $75 - $90 or so and would give you 3 distinctly different tuning options with which to evaluate the best match for your particular gear. That's three chances to improve the sound of your system for the cost of one pair of Teles! The ones that don't lock in are still a great investment by the way - if you change another component in the system in the future they represent great tools for revoicing the system. I cant stress this aspect of evaluating alternatives for yourself because depending on your system and your taste your conclusions on which tube is the best for you could be quite different. This was brought home recently when Jack G & I compared 4 of the group 2 tubes in both our systems - our conclusions were basically reversed! I was using them in a neutral line stage, he was using them in a romantic phono stage. So as always its horses for courses - and trust your own ears.

    What about the rarer more esoteric stuff? Well Id make sure I liked 5751s by trying the cheaper more common ones first, then I'd be opportunistic. You literally cant tell where or when they will pop up so you have to be patient and active in your search - who knows maybe you'll get lucky.

    Well, hope this helps. Next up (gads!) 6DJ8 family tubes...


    In my part 3 installation above, I identified the Raytheon as a 3 mica spacer design. It is in fact a 2 mica spacer with a "windmill" getter that looks more than a bit like a 3 spacer design on quick glance - I should have checked closer. The tubes Brendan at Tube World has are indeed the type I am referring too.

    The 6DJ8, 6922, 7308 Saga - Part 1

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

    Well this time Iíll be reviewing substitutes for the ubiquitous Sovtek 6922. That means it is 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 thatís 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 Iím 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. Iíve 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, Iíve 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 itís 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 6DJ8ís 6 volt rating. What does 6H23N mean? Who the hell knows! I sure donít.

    Physical Structure:

    The late 1950ís and early to mid Ď60s 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 tubeís internal structures. Next is the lower mica spacer itís 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 Iíve just described 90% of the 9 pin miniature triodes in the world itís above this point that things differ. The next structure up is the unique one itís a horizontal, circular, metal disc supported by two metal bars. Iíve seen & heard this referred to as a shield or a splatter shield. Which name is correct & what is the purpose of this structure? I donít 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 isnít a ring but instead is a two part metal structure made from wire in the trough 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 Ď60s through the Ď70s. 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 Iím not going to group tubes by quality, instead Iíll 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 couldnít live with it (but then I donít 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 itís 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. Itís 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 thatís 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 donít 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 Amperexes (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 donít 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 didnít 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. Iíll 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 shouldnít 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 ainít 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 Iíve 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,


    The 6DJ8, 6922, 7308 Saga - Part 2

    Posted by Joe S on March 30, 1999 at 20:08:00:

    Well, hello again! Weíre back with the rest of the pack, but definitely not a group of runner-ups. In fact the best of the lot are yet to come along with a few other genuine contenders so lets jump right into the fray...

    Mullard 6922 EE88CC, Great Britain (shield, gold pins) This is a Great Britain manufactured tube, not all of Mullards are in this family with a lot of these tubes being sourced form Amperex in Holland. As I understand it, Mullardís 6DJ8 tube tooling came from Amperex and it looks like it every Mullard in this family Iíve ever seen looks like an Amperex inside down to the smooth edge, slightly square shaped mica spacers. Perhaps as a result this tube owes a lot to the Amperex 6922 family when it comes to sound quality. This guyís got good bass, nice mids and a wet, ambient soundstage occupied by slightly smaller and images than the Siemens and Ediswans. A nice tube overall though not quite up to the level of the best Amperexes.

    Mullard CV 2493, Great Britain (no shield, getter disc, gold pins) This tube lacks a splatter shield with just a small metal wire holding a solid metal disc with dimples around its perimeter above the upper mica spacer. The sound of this tube is very different from the 6922 above, with a less pronounced bass and less vivid highs. It does have a very nice midband, however, combined with a deep & dimensional soundstage. If you find the 6922 Mullards (and Amperex 6922s to follow) too pronounced at the frequency extremes this tube could be a valid choice representing a viable tuning alternative...

    Mullard 6DJ8, Great Britain (shield, steel pins) One of my pair of these died a year ago (moment of reverent silence please....) so I couldnít compare it directly to the others in this shoot-out. Given the vagaries of long distance auditory memory I will not comment on specifics other than to say I remember it as quite good and worth checking out if you get the chance.

    Amperex 6922, JAN Orange label, US (shield, gold pins) A little sharp in the upper mids / lower treble. Good upper bass and highs. Vocals lack balance & body A bit disappointing. This tube sorta sucks...

    Amperex 6DJ8, Orange globe logo, Holland (shield, steel pins,) Much better than the above tube No comparison in fact. Warm, vibrant, lively, grainless, transparent Amperex sound. Killer tube. Almost as good as my reference Amperex 6922s (coming up soon). I slightly prefer this tube to the best of the Siemens 6DJ8s, 6922s & 7308s.

    Amperex 6DJ8, Bugle Boy logo, Holland (shield, steel pins,) Similar to the above tube with a slightly larger soundstage & more ambience, trading off a bit of impact and bass extension. I prefer the globe logo above to this tube by a small margin in spite of this tubes vaunted reputation. But still a good tube...

    Amperex 6DJ8, RCA, Holland (A frame, steel pins) - More forward vocals than the Bugle Boy. Sweeter highs too, with bigger, slightly less focused images. A little closer to the Globe logo 6DJ8 overall in character than it is to the BB....

    Amperex 7308, Orange globe logo, US (shield, gold pins) More focused and palpable than the Bugle Boy & A frame 6DJ8s. A bit like the Globe Logo Holland 6DJ8 overall. I still prefer that tube to this one but this is still a pretty good tube...

    Amperex 7308, JAN, green label, US (shield, gold pins) Very similar to the globe logo 7308 above. Both could use a little more bass kick & body to vocals in my rig, but could represent a useful tuning option in a system where my favorites come across a little too lively and forceful. While this tube is highly recommended by some dealers I think a few of the other Amperexes here slightly best it...

    Amperex 6922, PQ, white label, US (shield, gold pins) Another very good Amperex tube. Warm yet lively, focused, grainless and transparent. A winner one of the best. Dynamic with punchy bass to boot....

    Amperex 6922, PQ, white label, Holland (shield, gold pins) Slightly more forward midrange than the US version, above, pushing vocals a bit more forward in the mix. Otherwise, very similar. Another winner...

    Amperex 6922, PQ, white label, Holland, D getter (shield, gold pins) Another winner. Slightly less midrange emphasis than the round getter halo Holland above, with a bit more life. Good treble extension. An excellent tube...

    Amperex 7308 white label, US (shield, gold pins) My favorite 7308 by a small margin. Bass is a bit better than the Holland 6922s. Vocals lack just a touch of body compared to the best Amperex 6DJ8s & 6922s. Still a very good tube overall...

    Amperex 6922, USN, white label, US (shield, gold pins) Sounds very much like the US white label PQ. Another excellent tube though it may lack just a bit of that tubes warmth & body, but Iím quibbling here....

    Amperex 6922, Mullard, Holland (shield, gold pins) Sounds a lot like a Holland PQ white label. In other words a very nice tube with slightly forward vocals and a lively transparent sound...

    Amperex 6922, PQ, white label, US, pinched waist (shield, gold pins) Yeow! My reference tube. An absolutely gorgeous sounding tube with an unusual physical characteristic. The glass of the tube is actually slightly pinched at the about the point of the upper mica spacer. This reduces the tubeís diameter at that point resulting in a subtle hourglass shape. The reason for this was for the bottle to actually clamp the upper mica space at its rounded corners resulting in a more rigid, less microphonic, structure. The result? A tube that defines the Amperex house sound: Lively, transparent & detailed with extended highs, yet absolutely no grain, with a punchy, dynamic bass. Mids? Lucid and palpable, thank you. The best tube in the 6DJ8 family IMO. The only downside? These guys make the rare Siemens CCas look absolutely common in comparison. Cost? If you have to ask.. If I were hunting for a tube almost as good and much more accessible? Iíd hunt down some US white label PQs and live contentedly until the gods smiled on me and I lucked into some of these...

    Well, thatís it. And there are other Amperexes I havenít even touched on. While this particular manufacturer made some great tubes in this family, they were offered in an almost bewildering array and while there is a house sound there are some significant sonic differences among them. Now a word on Amperex chronology to help in your searches while I donít know it all, here is what Iíve been able to piece together so far...

    White labels the earliest tubes in this family had white labels. 6DJ8s had the Bugle Boy logo, or just the Amperex name in white, while 6922s were often labeled with the PQ logo in the shape of a shield. I have also seen the 6922 along with the 7308 with just the model number and Amperex name in white. All of these labels were very fragile and rubbed off easily.

    Orange globe logos Next up chronologically, these tubes have a reddish orange label printed in a fragile ink that rubs off easily. The logo included the Amperex globe (like the drawing on the yellow & green Amperex boxes) along with the model # and the Amperex name.

    Red or green labels these tubes used a thick paint like ink that will not rub off and usually just used text with no logos of any kind. You will often see 1970s JAN (military) tubes printed this way the Green label 7308 US for example.

    Why is this important? Well to my ears the best sounding Amperexes were the early ones (generally) meaning all else being equal Iíd be chasing white label tubes. Now there are some great globe logos, but some of them just seem to have a bit less of that Amperex magic, but hey thatís me. See what works best for you and chase 'em accordingly. Oh yeah. the best Amperexes were the US & Hollands in my opinion. You will occasionally see other countries of origin for their 6DJ8 family tubes - but IMO these two were the best and that's where I'd spend my money.

    Siemens vs. Amperex

    So how do the Siemens and Amperex stack up comparatively? Well, to my ears, the Siemens sound just a bit more linear, with just a touch less vibrancy and life and freedom from grain that are the hallmarks of the best Amperexes. The Amperexes sound just a bit more full bodied and lively on top and are a touch more romantic in balance. The Siemens also tend to throw up slightly larger images, the Amperexes slightly smaller, better focused images (but not small - don't get me wrong on this one). Both are exceptional tubes so I wouldnít hesitate to experiment with either. Which would I be chasing if I were hunting for some great tubes? Thatís easy both! :-)

    Danger Will Robinson!

    Be careful when you chase these guys. The reputation of Siemens & Amperexes precedes them and they are frequent targets for counterfeiters. How do you know if a tube in question is the genuine article? Well, fortunately there are a few basic checks you can perform to differentiate true Siemens & Amperexes from relabeled Sylvanias and Tungsrams.

    First, check the top of the tube in question. Siemens & Amperexes always have small ridges in the surface of the glass on top of the tube radiating outward from the nipple. These tubes will have 4 ridges, though sometimes only two of them are easily visible. The concept here is to look down on the top of the tube. The 2 or 4 ridges should divide the circular silver top of the tube in half or into quarters. No ridges? No genuine article pass on it.

    Second, check the metal shield above the upper mica spacer. On Siemens & Amperexes itís circular with two raised rectangular sections on opposite edges of the shield. On most fakes that shield is a perfectly flat disc.

    Third, about 90% of Siemens tubes have a 1 or 2 digit number molded into the inside bottom of the tube glass centered between the pins. It can sometimes be very hard to see but itís usually there. Remember, not all Siemens have it, but if your tube passes test one & two and has the number(s), it's a Siemens.

    Fourth, familiarize yourself with the shape of the glass bottle on your stock Sovteks. Note that the top is smooth (no ridges) and rather rounded and the tube is short & large in diameter these traits are common to all Russian tubes in this family. Siemens & Amperexes are only about 80 to 85% of the diameter of the Russian versions and tend to have squarer shoulders on top rather than the rounded top of the Sovtek. You should be able to spot the difference between a Russian and a genuine NOS tube just by the shape & diameter of the glass pretty easily. One warning though Sovteks often (always?) have a number molded into the bottom of the tube between the pins like a Siemens, so know all the checks and donít depend on just one to verify the tubes origins.

    Fifth, if itís a Siemens or Amperex 6922 or 7308 it will always have gold pins. So will some cheap counterfeits, so gold is no guarantee. But if they arenít gold its not a Siemens or Amperex, so pass on it.


    Be careful of getting hung up on the brand name printed on the tube. In my experience most Siemens 6DJ8 family tubes you will find in the US are labeled anything but Siemens. Why? Siemens (and most other manufacturers) served as an OEM (original equipment manufacturer) supplying their tubes to many other tube manufacturers. While Siemens made these tubes they were labeled with the name of the company they were supplied to RCA or Phillips for example. Now not all RCAs and Phillips were supplied by Siemens, so thatís where points 1 5 on how to check tubes comes into play. Fortunately, in many cases the tubes are labeled with the county of origin & that can help you identify a tubeís manufacturer. Made in West Germany? Itís usually a Siemens. Made in Holland? Probably an Amperex. Made in the USA? Usually a Sylvania or an Amperex. Oh yeah a useful tip: RCA never made 6DJ8 family tubes. If itís an RCA and has a ridged top itís either an Amperex or a Siemens. Iíd watch this brand closely if you stumble on it. Many tube dealers will sell lowly RCA 6DJ8 family tubes for $15 to $20 a tube without realizing that there is European made gold inside. Check the tubeís top for ridges, the label for where it was manufactured and if everything checks out, buy it! This is one of the absolute bargain brands in this tube type.

    Amperexes were also frequently OEMíd to a variety of manufacturers. Most commonly to Mullard, DuMont, Beckman, Hewlett Packard and a few others. The risk with Amperexes is that they do vary by vintage and model and itís hard enough to keep that straight among Amperex labeled tubes. Which vintage / version are you buying under another manufacturers brand? Who knows? Itís just pot luck.

    My biases

    Take my comments within the context of my system which, although CD based, is neither grainy nor euphonically rolled off on top. As a result I value good high frequency extension as it comes through in a clean, grainless and non fatiguing manner. I also like a dynamic, transparent and lucid sound with dimensional images within the soundstage. I also like to have the performers in the room with me so I like a slightly forward, but still non fatiguing balance. If your rig is bright and forward you might want to skew towards the tubes which are softer on top & a little more laid back than my favorites. But frankly, if you are using Sovteks now, this shouldnít really be a big problem.

    Well, that it folks. I hope you find the overview helpful or at the very least thought provoking & hey, if I trashed your favorite tubes - donít worry about it! Itís just one tube freaks opinion. If they work for you, thatís all that counts.

    Good luck!