玩5751，找5751的朋友必看。
相信会很有帮助的。
就是要动英文。
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....
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.
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
- I抦 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 I抦 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.
