12AX7 overview of current production

Discussion in 'Amps and Cabs' started by myles111, Jan 4, 2008.


  1. myles111

    myles111 Member

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    I thought I'd post this here as there may be some folks that were interested....

    12AX7 types at a glance:

    Preamp tubes .... a few bits of info:

    I received a question from one of the folks on a forum in late 2007 who wanted to retube his whole amp. For his objective I felt it was not necessary to replace every tube. He was making some classic mistakes and after giving him some guidelines and suggestions I felt that some of what I wrote might be beneficial for others.

    On preamp tubes ... this is all personal preference but you DO NOT need to change them all. Experiment with V1 ... the tube most close to the input jack. This is 85% of the tone and gain in your amp and has the most effect.

    Again ... this is personal taste but a little guideline here is:

    12AX7R - lowest gain and darkest. Generally better in current driver spots such as effects loops or reverb circuits rather than in the front end. This tube is also known as the Sovtek 12AX7WA and Sovtek 12AX7WC. The gain of the WA is lower than any other 12AX7 type. The gain of the WC is about average compared with other 12AX7 types.

    12AX7R2 - smooth but not bright, sort of mid range in response. Average gain. Great in phase inverter positions too. Also known
    as the Sovtek 12AX7LPS. How a phase inverter breaks down and passes signal to the output section can affect the tone and feel of your amp. I know some say the phase inverter has no effect. I disagree and am happy to demo this to others and let them decide. In any case, my personal preference in many cases in a longer plate tube for the phase inverter in amps that use 12AX7 phase inverters. This is also a great front end tube for some tastes.

    12AX7R3 - bright and articulate. Average gain. Can sound a bit thin to some ears in some amps. This tube is also known as the 12AX7EH (Electro Harmonix) and with a slightly different internal structure also known as the Tung Sol Reissue. These tubes are all over the map on specs so if you buy a EH or Tung Sol version get them from a trusted vendor that tests them well. If you get these in the GT Gold Series they are already tested for noise, output, etc. and will be within a good spec range.

    12AX7C - Chinese 12AX7. The most smooth and linear of the 12AX7 family. A lot of Marshall folks swear by these and in Fender
    type front ends are really nice. Make sure you use generation 9 only. Generation 7 and 8 are not as nice. Some early generation 4 tubes are prized by some high gain amp folks. There are a lot of "Chinese" 12AX7s on the market and lots are Gen 7-8. There are also a lot of Chinese tube companies and co-ops such as Sino. These are a great all around tube when selected by a good vendor. GT has nice ones but another great vendor of super 12AX7C's is www.arselectronics.com as their process is top notch and their prices are great. ARS also performs reliability testing on every incoming batch of tubes they sell so they are one of the few folks aware when a new run is garbage. These are also the tube I select for tube preamps or amps with tube front ends and solid state power sections. This is also my pick for bass amps with tube front ends.

    ECC83S - This is the JJ produced tube and has a short plate design that is very free of physical microphonics. These have a different mid range response than other 12AX7 types. They are the most gainy of any of the 12AX7 family and the tubes that have the highest percentage of ones that fall in the 85+ actual gain spec. The gain of a 12AX7 should be 100 at 250 plate volts with a 2 volt bias but most tubes made today are 75-80 or so. Many of the ECC83S tubes exceed a gain of 90. Just a five point drop in gain in the front end of many amps will turn the amp into an OK amp rather than a great amp as this is the main tone and gain stage in many amps. These have a classic British response; Vox, Marshall, Selmer etc. These are what I use to build the SAG-MHG kits after hand selecting for gain, current output, transconductance and plate resistance.
    Ei 7025 long smooth plate - Not available at the moment from GT or perhaps anybody else as Ei is getting back on it's feet but ... if
    you can find any of these out there they are the highest gain 12AX7 tube around but tend to be physically microphonic in many amps and if they are working nice today it is no guarantee that they will work that way tomorrow.

    12AX7M - GT has re-tooled this tube almost a dozen times in the four or so years since it's release to make it more consistent, more stable, and just better in every way. They were out of stock for a long time and will be back in January of 2008 with any luck.

    In the most recent batch I tested (in production now), the gain is now on par with the ECC83S. They are smooth and in Fender tolex era amps are just terrific and with a Tele will tame the brightness. There is a following of Marshall and 5150 folks that love these in their amps in the past and they look to be much more stable now. This is the tube that I use most often in the SAG-MHG kit as the phase inverter, the third tube in that three tube set. It is a long plate tube so I also like these in phase inverter positions along with the 12AX7R2 (Sovtek 12AX7LPS) as my other preferred tube for PI use. This is a GT exclusive tube.

    5751M - Think of this as a lower gain (about 70) 12AX7. This is a tube to use in V1 when you want more clean headroom and a
    smoother response. This was one of SRV's tricks in the first gain stage of some of his Fender amps. This is a GT exclusive tube.
     
  2. Hipster Dofus

    Hipster Dofus Member

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    Cool.

    Any news on a new EF86?
     
  3. riffmeister

    riffmeister Gold Supporting Member

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    Hi Myles, how long do "matched triode" 12AX_'s stay matched? And does it depend on what position they are used in?
     
  4. myles111

    myles111 Member

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    I think that is almost the same question as how long does a preamp tube last.

    Generally they stay within match for years. I have seen more examples than I can count of good original preamp tubes in amps from the fifties and early sixties where the tubes test better than the new production tubes test today in most cases.

    In most amps other than in the phase inverter, the two sides of the tube are used in completely different applications within the circuit so matching is of no benefit and there is no need for a matched dual triode.
     
  5. myles111

    myles111 Member

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    There are a few of them out there and I have posted some of my test results in various places. Nothing from my point of view to write home about but some good stuff is out there.
     
  6. doublee

    doublee Member

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    Question on V1: isnt that useful only if your are using the normal channel in a Fender?

    thanks,
    ee
     
  7. hamfist

    hamfist Member

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    +1 !!
     
  8. myles111

    myles111 Member

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    Thanks ... have a great 08 !
     
  9. stratzrus

    stratzrus Philadelphia Jazz, Funk, and R&B Supporting Member

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    Thanks for the helpful info Myles...always glad to read your posts.

    stratzrus
     
  10. myles111

    myles111 Member

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    Yes.... V1 in a blackface is the Normal channel and V2 is the Vibrato channel.

    In most amps V1 is the first gain stage.

    In the Fender Hot Rod Series V1 is also the first gain stage.

    I guess one could be more accurate to say if one wants to experiment with tone changes try tubes in the first gain stage.
     
  11. doublee

    doublee Member

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    Sorry to be a pain: So if I only use the vibrato channel in a DRRI for instance, then V1 has little bearing on that channel and a cheapish (or even no) tube will suffice in V1? If I read the KCA site correctly I believe thats what he says. I have your site dialed up and am starting on it...theres lots of stuff there,

    thanks,

    ee
     
  12. midnightlaundry

    midnightlaundry Member

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    You're very generous with your knowledge. Thanks! Glad to see you endorse ARS. I just ordered some of their ARS brand filter caps. 'Hope they work out. :D
     
  13. SQUAREHEAD

    SQUAREHEAD Supporting Member

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    Hey Myles!

    I have 75 older late 80's (square getter) Chinese 12AX7's that are all
    in the highest gain category of any tubes I have tested.
    Are these considered different than the 9th Gen tubes and the other Chinese 12AX7's??

    They sound amazing to my ears... much better than other Chinese ones I've tried...
    Just wondering why??!!

    Thanx

    Keith
     
  14. frank4001

    frank4001 Member

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    Thanks Myles....Can you tell us who makes the the 12ax7 that is closest to original 12ax7 specifications? I read where new ones fall short in some area like gain ect.
     
  15. myles111

    myles111 Member

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    You are correct.

    Many folks remove V1 altogether as it will let the plate voltage rise a touch on the other tubes. You can also think of V1 as a "spare" 12AX7 always available to swap with another of the 12AX7s if there is a tube problem.
     
  16. myles111

    myles111 Member

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    Their caps are pretty terrific. Their "Marshall" caps ... LCR style are excellent.

    When it comes to tubes they have been around a heck of a long time. GT has been around since 1979 but ARS has been around since 1947! Their matching is terrific but they also stress test tubes from every batch they receive with insane voltages. If there is a problem they know it. Their tubes typically show very long service life when compared to some other folks selling the "same tube" due to their testing methods.

    They are a good place for transformers, speakers and other parts too.

    Yeah ... I am pretty sure you will be happy with their capacitors.
     
  17. myles111

    myles111 Member

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    Keith,

    There are a lot of folks that think of the older Chinese 12AX7s as being the holy grail of the 12AX7C tubes. They were higher in gain and met spec much more often. There is even something of a cult following that is into what they call NOS Chinese 12AX7s from the eighties.

    Things have changed due to materials that are not as pure and faster production with less time for QA. The old 12AX7s from China were pretty darn nice.
     
  18. SQUAREHEAD

    SQUAREHEAD Supporting Member

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    Thanx Myles...

    Are these "nos Chinese" all square getters ?? I mean... Is that the way to tell them apart from others?

    Keith
     
  19. myles111

    myles111 Member

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    Frank,

    This changes from run to run and batch to batch.

    What is generally true, and true at the moment, is the JJ ECC83S is the highest gain 12AX7 that is currently in production. Most 12AX7s today have a true gain of 80 or less on average at 250 plate volts with a 2 volt bias. The JJ has many over 85 and I have seen a lot over 90 and have hit 105+ on some in some batches.

    One of the lowest gain tubes is the Sovtek 12AX7WA. The Sovtek 12AX7WC is not in the same class. It is average in specs with most of the other folks and is a good tube if you like the tone.

    The long smooth plate Ei was the highest gain of anything out there. High gain and sloppy construction makes the tube physically microphonic a lot of the time but when you find a good one they are great.

    The GT 12AX7M originally had great gain in the first tooling run or two. For the next 8 tooling changes it had the lowest gain of anything out there. The tooling change that was done from October to December finally got things to look right. Now the tube has gain on par slightly above the average production 12AX7, maybe like a good 12AX7EH as an example but darker in tone than the EH or Tung Sol reissue.

    The JJ is still, at the moment, the most proper spec tube with the highest gain. That is the tube I use for V1 and V2 positions in the SAG-MHG kits I build for my clients and that GT sells as it is the only tube out today that can produce a gain of above 85 in decent enough quantity to make selection possible for a decent amount of tubes in 100. In 100 JJs I can get about 40-50 over 85 in gain. On the others it would be less than 20%.
     
  20. myles111

    myles111 Member

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    Keith,

    First off ... have a great 08.

    Square getters are not always the key. There were solid round getters and halo getters. The key to identification visually at the basic level are the shape of the micas at the top of the plate structure. I step people though this over the phone. If you call me during the week at 1-800-459-5687 between 8am-11am pst at GT and have one in your hand I will step you through this. I do this a few times every week. If I could take decent photos I would put up something that explains this for folks.
     

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