Did you ever read this: http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.htmlMy own ranking of 12AX7's (and 5751's) is slightly different than Joe's, but one thing I totally agree with, is that even the best 12AX7's are kind of grainy compared to the best 5751's -- to the point that I don't even bother with 12AX7's anymore. And when it comes to phonostages, 5751's are definitely the way to go (for low noise and great detail.) It's true that 5751's are spec'd at 70-80% the gain of 12AX7's (driven at full bore!) but no one has ever reported a problem on that score, not even in phonostages where gain is so important. . |
FBI: A lot of folks really like the GE 3-mica blackplates. Is that what you have in your Jolida?
Phil and Bicycle:
The TFK 12AX7's were the first tubes I replaced in my new McIntosh MC275 -- and boy! did they make a night and day difference. (McIntosh used to use TFK's as OEM tubes back in the day ;-(( They are good tubes, but waaay overpriced these days IMO. I guess my favorite AX7 was the RCA 17mm long blackplate. |
Abucktwoeighty -- I can't say for sure about your CDP application, but let's just say don't count on less output because you're running 5751's ;-)
If you compare performance (tube) curves between a 12AX7 and 5751, you'll note that the curves are essentially the same until the upper limit of operation where the 5751 drops of some. HOWEVER, I don't think any circuit designer would use either tube where it would be driven to the limit -- there would be other tubes to choose from.
Also, keep in mind that the 5751 was originally developed as a 'ruggedized' tube for the military - so it would have to perform the same as any 12AX7 it would replace. |
Magnum, the reason audio people like the 5751 (or European 'CV' military) version of the 12AX7 is because they have been 'ruggedized' for military use -- which (as a byproduct) makes them free of detectable microphonics, especially the ones with the 3-mica construction. This is more or less important in audio depending on the application -- phono and microphone preamps being the most critical.
The fact that 5751's (generally) have a smoother presentation is just icing on the cake.
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Magnum, I do think stronger is better for the reasons I already detailed. I believe what you're saying is that stronger doesn't necessarily mean better SOUNDING, and except for the 3-mica 5751's near total lack of microphonics, I wouldn't argue with you.
I also mentioned (and this is admittedly my own experience) the fact that for reasons beyond my understanding, the 5751's (generally) have a smoother presentation than the 12AX7's I've heard (which in my case includes most of them.) "Smoother" being my own term for a less grainy or maybe more liquid(?) sound. YMMV
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I had to laugh at Rodman's recommendation of the EAT 12AX7 as the only acceptable current production 12AX7. Oh, I'm sure it's an excellent sounding tube (haven't heard one myself) but what made me laugh was the fact that it costs $225!! So much for saving money by buying current tubes! (I was also amused that Music Direct thinks it best to hide the inside of the tube in their web photo;-) I actually did audition some (used) EAT KT-88's and they were terrible!
If you want a great pair of ANOS (almost new old stock;-) 12AX7's I have at least 1 pair (maybe 2) of RCA 17mm long blackplates I'd sell for half of a single EAT, and I bet you'd like them better than the EAT or any of the usual NOS suspects, BUT it really depends on where you're using 12AX7/5751's which I don't think you mentioned?
My favorite 5751 BTW is also the RCA TMBP (after endless A-
B with the Sylvania TMBP.)
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To quote Ivor Tiefenbrun(founder of Linn Products), "If you gaven't heard it, you have no opinion."
Right! And good luck getting anyone to send you a demo tube so you can form an 'opinion'! I'm more interested in how these TechTubes will sound. They should be ready (finally) to release them this month: http://www.techtubevalves.com/The have a new (for 9-pins) internal structure that uses CRT technology. And at $30 a pop (or so) I'd be willing to try a couple ;-) . |
I disagree that you'll need to compensate for the 5751's slightly less gain; because that difference doesn't really occur until past the normal operating range on the two tubes' curves. Most people can't hear any difference, and the military (who originally requested a 'ruggedized' 12AX7) wouldn't have traded that requirement for a loss in performance when they replaced their 12AX7's.
As for tone, that really depends on the specific tube and to a (lesser) degree on the make of amp. I specify 'amp' because that's where the tube produces the most gain and so the tonal qualities are most obvious. In a preamp, what you are looking for is low noise -- especially in tube phonostages where a 5751 might be a plus.
I don't have tube preamp/phonostages, but the majority of my friends with McIntosh tube preamps (with tube phonostages) seem to have settled with Telefunken AX's and AT's over the stock Chinese tubes, and haven't ventured much beyond that. People with hissy tube phonostages who can't find a quiet 12AX7 and/or 12AT7 should definitely try 3-mica 5751's and/or 6201's (and tell us what happens please ;-)
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Rodman, when did I ever say they were the same tube? Anyway, if you're talking about the (little used) "amplification factor" curve, yes there is a slight difference, but if you look at the transconductance curves (Gm), the standard measure of gain, the two are almost identical, in fact the 5751 shown in the curves I saw was actually a little higher. Anyway, no (tube) circuit designer in his/her right mind would drive a given tube into that portion of its operating range in the first place.
Having said that, it's well-known that ARC drives their (power) tubes quite hard while McIntosh is quite easy on tubes; which is why you've yet to see a Mac tube amp with mechanical ventilation ;-) |
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R -- I know, don't ya just hate when that happens! ;-) |
RE what Larry just said about the premium TFK, I have a general 12AX7/5751 question/poll(?) for those familiar with both (hopefully, but not necessarily, in the same piece of equipment ;-) In his famous "Tube Lore" article on AA, http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html Joe asserts that he could never really find a 12AX7 he liked. He lists some preferences, but compared to his favorite 5751's, he finds all 12AX7's "grainy" (I think his word was.) I maaaybe understand what he means. However I've rolled many different 12AX/AT7's and 5751/6201 in my McIntosh MC275, and like Larry, I've learned that to have blanket prejudices/preferences may not lead to the best choice - my love for the GEC A2900 being a perfect example (I never would have tried it if I'd decided to only go with 6201's.) So does anyone agree with Joe's take on the issue: that 5751's are better across the board than 12AX7's? Just curious ;-) . |
Thanks Larry. Anybody else want to chime in?
I'm listening to horns today (recordings), so maybe that should be 'honk' in ;-) |
I know none of you will believe this (until you try it!) but the best way to clean tubes, and especially European tubes with that delicate white printing, is naphtha (as in: Ronsonal lighter fluid.) Anything with even a hint of water in it (almost all alcohols, Win dex, etc) will dissolve the white paint, but not naphtha. |
B-man I've heard rumors (un-verified by me, mind you) that the BB's with the permanent labels (not the Amperex orange globes) might be fakes. I would suggest doing a bit of research first. I could be wrong of course, however I find "Trust but Verify" to be an excellent approach (in many areas of life actually!)
BTW, according to my techie friend Stephen Sank, any of the minitriodes that say Herleen Holland are out of the same Amperex factory? Just different labels/brands.
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B-man, we were all beginners once, and although people have to have their own learning experiences, it doesn't hurt to ive folks a little heads up.
As for current ('reissues') vs. NOS (honest people now call them ANOS = almost new old stock = slightly used old stock ;-) Honestly, slightly used is a better bet than brand new old stock because at least the slightly used are proven working. If I were buying expensive BRAND NEW old stock tubes, I'd make a deposit but then insist the seller
test and burn-in the tubes for a few hours before shipping them to me ;-)
As for their sound, the current issues aren't bad, and I'm sure they will slowly get better. The brands bought by the American fellow who owns New Sensor in russia are: Sovetek, Genalex Gold Lion, Electro Harmonix, Svetlana, Mullard, Tung Sol, and a few other I forgot. None of them are like the originals (internally) although some are built very substantially.
The real difference between the old and new is metalurgy. The old-timers who experimented for years and years cooking up new (secret and jealously guarded) plate coatings had no one to pass the secrets to when ss came along. So the craft died with them. They succeeded in achieving very high plate current at rated voltages that tubemakers today can only hope they'll get to one day.
As an example, a typical NOS Genalex GEC or Gold Lion had transconductance values (when new) of 10,000 umhos or more (that's the measure of a tube's gain). Today's best KT-88's, the Genalex or the Shuguang/Penta-Labs (the Penta is an exact copy of NOS tube) when they are brand new are 7000 to 7500. I have some USED NOS Genalex theat are 9000! So it's not so stupid to buy he older tubes and some of them have a sparkle to them than so far no current tubes can duplicate. Anyway that's the basic story. There's tons of history and lore available today at the click of a mouse.
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Larry, one day I just said, "this really sucks!" and I got some Q-Tips, gathered a few old European tubes that had almost no printing left, and set out to try every solvent I could think of to see if anything would spare the printing. Naphtha was IT. And no surprise really -- that's the only solvent dry cleaners will use on your clothes!
I should have noted that even the moisture in some peoples' skin can take off the printing, so it's best to handle those with really fragile (almost gone) labels with a clean cotton cloth or latex gloves before and after cleaning.
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Bob, the RCA 5751 TMBP is my favorite 5751 (it's a REALLY tough call, but I still think I like it better than the Sylvania.)
I have mine in a Mac amp, but in a phono stage did you notice:
A. Any reduction in gain? Many are concerned about this, personally I don't think it would show up unless one is driving the tube over the brink!
B. Any (noticable) reduction in noise floor - you did say "clearer", so that might could be lower noise floor? |
Bob, "ruggedized" (for the military) 5751's (especially the triple mica ones) are supposed to be great in phono and microphone preamps because of their extremly low noise and/or microphonics compared to a regular 12AX7. Something I can't really judge as mine are in an amplifier. However, they are definitely smoother (by which I mean less in-your-face grainy) than the 12AX7's I've tried; and the really good 5751's are more dynamic too. -- Neil
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Bicycle_man, isn't that queen just too much!? It cracks me up every time I see his auctions! Bob, I applaud your reminding us all of this: . . . but making sure to go back and see if a change is ultimately an improvement, or just a change. Human beings being the stimulation junkies we are, changes often seem 'better'. For at least a minute!! Geary, I have also been cautioned about using 5751's if they would be in (active) RIAA circuits. Apparently passive RIAA circuits are not affected. Neil . |
Bicicyle_man, in fairness, I have seen "museum quality" TFK 803S's go for as much as $1400 a pair on eBay (before the financial meltdown!) They ARE rare, and if one is a collector (and has no intention of using them - which blows my mind ;-) I suppose . . . . . .
But if you were to do a little research as I did, purely out of curiosity (I wondered what a $1400 pair of 12AX7's must sound like?) you would probably discover as i did that the concensus was "nothing special"!
The only time I [almost] got badly burned buying NOS tubes (the seller took them back ;-) was when I paid a premium for some truly NEW NOS tubes and one was a complete dud. But nobody knew because no one had ever tried to use them! Oh yeah, the seller had tested and measured them, but not actually placed them in service in a component. From then on, I only buy ANOS (almost new old stock) tubes with at least a few hours on them. There's nothing like a 'track record' when it comes to tubes! |
