ChemMan

Tube rolling with 12AT7 and 12AX7A on MA252 preamp

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Posted (edited)

Fellow listeners,

I'm hoping to expand my knowledge base and receive some recommendations in order to swap out the tubes on the pre-amp section of my McIntosh MA252 Hybrid integrated.  Nothing at all is wrong with the tubes or amp.  I like it very much.  I'm interested in how to move forward with purchasing tubes to replace the Tesla stock tubes it came with.

Here's what I know so far:

1. My research reveals that the difference between the 12AX7A and the 12AX7 is based on the type of electrical configuration in the tube heater circuit.  The 12AX7A will work in series and parallel where as the 12AX7 is good for only the parallel designs. I asked about the circuitry in the MA252 and the good fellows at McIntosh responded with: (apparently a series circuit has not been used in years?)

The original 12ax7 from the 1940s does not have the same performance as the later 12ax7a.

I am not aware of any company making the original 12ax7 for over 60 years now so we would assume a tube newer than the 1950's production should be a 12ax7a version. Some companies call them 12AX7 and others 12AX7a, but a modern tube with either designation is ok to use

2.   I Found a veritable treasure trove or Pandora's box depending on your perspective.  http://www.audiotubes.com/12ax7.htm They give a very detailed description of brands and their general sounds.  It seems US tubes are less expensive than European and AX7 are more rare and than AT7.

3. What part of the pre-amplification process in which the two different tubes (AX7 and AT7) take part is unknown to/beyond me.   I scoured sites all day.

I'm hoping to enlarge the sound stage and.............??

Any assistance is most appreciated.

Edited by ChemMan

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Any 12AX7 will be fine. They are all capable of operating in series or parallel heater circuits and the stuff about early ones is simply that some varieties were made with 'slow warm' heaters. Some modern designs still use series-wired heaters (EAR834 for example) and take any 12AX7. The A, B, WA and the rest sometimes depend on the maker and don't always mean the same thing.

Be slightly wary of Brent Jesse's 'equivalents' by the way. He's very keen and has an immense range, but he can sometimes be a little 'loose' with his ideas of what is actually a direct replacement.

Basically, any 12AX7 of any designation is fine. Any ECC83, ECC803 is fine. Any 7025 is fine. A few others are OK, but so rare it's pointless mentioning them.

As for 'sound', it's been said a million times. Valves do not have a sound. It always depends on the circuit they are in and what sounds excellent in one may sound ordinary in another. However, generally now avoid any 'NOS' very costly tubes. There are a lot of fakes or poor ones around. The really costly NOS stuff is really costly because of hype and because of collectors. There is absolutely no way an early, smooth-plate Telefunken 803S is worth over $1000. I know.

For the 'good' stuff that's not insane, older tubes: Siemens, Mullard, Amperex/Bugle Boy, Telefunken. From the new production stuff, be careful because quite a lot are excellent in guitar amps, but are not that good for audio. Most are fine. JJ are universally decent, and the JJ Gold Pin ECC803S is one of my favourites. In some circuits, I rate them as close to some of the insane money NOS valves.

Basically, YMMV. Don't go insane expecting massive differences. Some will be better than others and if possible (anyone here?) find someone with the same or very similar amp who has tried.

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9 hours ago, rabski said:

For the 'good' stuff that's not insane, older tubes: Siemens, Mullard, Amperex/Bugle Boy, Telefunken. From the new production stuff, be careful because quite a lot are excellent in guitar amps, but are not that good for audio. Most are fine. JJ are universally decent, and the JJ Gold Pin ECC803S is one of my favourites. In some circuits, I rate them as close to some of the insane money NOS valves.

Thanks Rabski, I was counting on your encyclopedic knowledge of valves for advice.

I was thinking about budgeting a maximum of $250 a pair and $500 (my DAC search remains on hold so I have a bit of cash) for the four, but as I have zero idea of how they will sound am wondering if spending a lot less is the way to go. There are a fair few Telefunken on Brent Jesse's site as well as all the other European brands you mentioned.  Given what you said about guitar amps, my guess would be to try NOS tubes rather than new production?  

Fire away with your thoughts, caveats, recommendations. I would prefer to purchase here on the continent or online thru the UK, but don't know any reputable dealers.  My tentative plan was/is to roll the dice and buy them in the US and my brother brings them over when he visits in the summer.

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Good European NOS are the most sought after, no need to go to the USA.

At (up to) your money be looking for box plate Mullard ECC83 which are rare and expensive as NOS and worth every penny if you like a rich sound. Since nobody produces their construction type elsewhere, 'bargains' on eBay are unlikely to be faked and an adequate risk on the assumption that some may be shagged, but they do last for ever...

Telefunken short ribbed or long smooth plate are both excellent as are Siemens and Halske (but not later production) or indeed most Philips group valves.

Pre JJ Tesla E83CC are superb, frame grid, near equivalent of the legendary Telefunken ECC803S at a small fraction of the cost, available NOS, and reliable, no need to match them just use them straight out of the box, production tolerances were fantastic and low noise to boot.

Just my tuppence

Sent from my BLA-L09 using Tapatalk

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2 hours ago, Jazid said:


Pre JJ Tesla E83CC are superb, frame grid, near equivalent of the legendary Telefunken ECC803S at a small fraction of the cost, available NOS, and reliable, no need to match them just use them straight out of the box, production tolerances were fantastic and low noise to boot.

Any idea how to find these online?  OR any reliable online purveyors in general.  In the UK I found Watford valves, Langrex, Hotrox.  They would all ship to Belgium.  I'm having less success finding vintage tubes here on the continent.  

Do you have any thoughts on new production brands like the reinvented Genalex old Lion or JJ?

@rabski Given the limited difference in sound a $1300 Chord Qutest made to my system, I am thinking that spending more than $200 total for the four tubes is probably a bit silly.

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I have Vincent integrated and headphone amps, and recently replaced the 12AX7's in each unit with Mullard ECC83. The difference is amazing and worth every penny for me, wider and clearer soundstage, and sweeter treble are just for starters.    However... they replaced Chinese tubes of unknown manufacture so YMMV as I would expect your Tesla tubes to also be far better than those.   

I have an ECC83 spare which I ordered by mistake if you're struggling, unused.

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2 minutes ago, paulkebab said:

I have Vincent integrated and headphone amps, and recently replaced the 12AX7's in each unit with Mullard ECC83. The difference is amazing and worth every penny for me, wider and clearer soundstage, and sweeter treble are just for starters.    However... they replaced Chinese tubes of unknown manufacture so YMMV as I would expect your Tesla tubes to also be far better than those.   

I have an ECC83 spare which I ordered by mistake if you're struggling, unused.

I made an order from Langrex yesterday for the 12AT7WA / ECC81 PHILIPS / MULLARD NOS MATCHED PAIR . They were only thirty pounds sterling. So I didn't mind taking a chance. Apparently the AT7 is responsible for phase. Two down and two more to go. 

I was doing more research about the 12AX7/EC833, and as my wife is Czech we plan to look for the NOS Tesla at the end of the month when sh goes back to her home town. Here is a very informative piece about the backstory and how to tell the JJ fakes from the originals, and how they are probably as close to the revered Telefunken as anyone ever got.

 https://jacmusic.com/techcorner/ARTICLES/English/Portraits/E83CC/ECC83-part-numbering1.html

My understanding is that JJ makes the tubes for McIntosh ( I found this info on another forum) so if worse comes to worse I was thinking about trying out Rabski's recommendation of the Gold Pin version.  I was also considering the new version of Gold Lion, but at 40 euros for one, I figured I'll keep looking for NOS for awhile. 

Also, thanks for the kind offer.  I'll see how things play out.

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Jazid's suggestions I would definitely agree with. For sources in the UK, Langrex are fair for NOS stuff and carry normally a reasonable assortment of unusual bits and pieces. Watford Valves are hard to beat for new production. Considering your location, for new stuff I'd also try Audiophonics (France). They have a reasonable range of valves and a seriously good range of other stuff.

New production? Opinions vary and it's often a minefield, because many are actually exactly the same valves with different printing. Also, some change the actual supplier so it's not always clear. As before, I've had very good results with the JJ Gold Pin 803S and one or two manufacturers swear by them. People have good words about the Gold Lion reissue, but whether it's worth the extra over the JJ is a guess (well it is for me, because I haven't tried the GLs). I have generally not had good experiences the few times I've tried some of the 'wonder tubes' from far east manufacturers, but YMMV. Whatever way you look at them, paying £60-£70 for a new production 12AX7 seems daft...

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1 minute ago, rabski said:

Whatever way you look at them, paying £60-£70 for a new production 12AX7 seems daft...

Thanks Rabski.  Update in post above.

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Posted (edited)
5 minutes ago, ChemMan said:

Thanks Rabski.  Update in post above.

Just seen it! I can't find the Mac schematics anywhere, so it's a guess. That said, 12AT7 (ECC81) as a phase splitter doesn't sound unlikely. If that's the case, they're probably not going to make that much difference sonically, and the 12AX7s will probably do more.

Mullard ECC81 should be fine as a phase splitter.

Edited by rabski

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1 minute ago, rabski said:

Just seen it! I can't find the Mac schematics anywhere, so it's a guess. That said, 12AT7 (ECC81) as a phase splitter doesn't sound unlikely. If that's the case, they're probably not going to make that much difference sonically, and the 12AX7s will probably do more.

Mullard ECC81 should be decent cearinly in that application.

I figured the same, but clearly from an intuition standpoint as I read they are responsible for the gain.  

I had no idea the vastness of the tube/valve domain and the history of it all.  It's fabulously interesting.   I'm really looking forward to tracking down a couple sets of the 12AX7 and hearing what it might do.

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On 02/05/2019 at 16:56, ChemMan said:

Tesla E83CC are superb, frame grid, near equivalent of the legendary Telefunken ECC803S at a small fraction of the cost, available NOS, and reliable, no need to match them just use them straight out of the box, production tolerances were fantastic and low noise to boot.

My serious=minded wife got busy and in just a matter of hours found a couple back in the Motherland.  She ordered me two, tested NOS, for 118 euros.  They will ship on Monday.  I should get them on Wednesday.  Now, I'm a kid ready for Christmas.  All told I came in 40 euros under my second budget.  Report to follow.

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:pop::)

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14 hours ago, ChemMan said:

My serious=minded wife got busy and in just a matter of hours found a couple back in the Motherland.  She ordered me two, tested NOS, for 118 euros.  They will ship on Monday.  I should get them on Wednesday.  Now, I'm a kid ready for Christmas.  All told I came in 40 euros under my second budget.  Report to follow.

Be good to hear what you think .Ive found,not all of the best 12ax7 ,ecc 83 sound the best .Depends on if your amplifier likes them ,and of course your ears.Got some nos that are expected to be up their with the best ,they dont sound great in my amp.Ge Jan 5751.Ray black plates.Amp bugle boys did not sound great in my set up .But Telefunken ecc83 and Mullard m8137 sound amazing.Lovely to play.if money lets.My amp only uses one 12ax7 tube.Went through 12 differant types ,before i found what sound i wanted.

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1 hour ago, mattykyuss said:

Be good to hear what you think .Ive found,not all of the best 12ax7 ,ecc 83 sound the best .Depends on if your amplifier likes them ,and of course your ears.Got some nos that are expected to be up their with the best ,they dont sound great in my amp.Ge Jan 5751.Ray black plates.Amp bugle boys did not sound great in my set up .But Telefunken ecc83 and Mullard m8137 sound amazing.Lovely to play.if money lets.My amp only uses one 12ax7 tube.Went through 12 differant types ,before i found what sound i wanted.

Let's hope it goes a bit better faster than twelve. Yet, everything I've read says you are spot on and there is no real way to predict.  I hunted thru every post I could find on every forum concerning the MC275 to see if somebody has fooled with those tubes as they are the same as mine.  My amp is so new there is not much out there about it.

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