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Blues Jr. / 12AX7A vs. 12AX7 replacements?

Discussion in 'Glowing Bottle Tube Amp Forum' started by Pasta Player, Jan 25, 2021.

  1. Pasta Player

    Pasta Player Tele-Meister

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    2 y/o Blues Jr. (mfg. 2018) major volume loss after about an hour of play. Now only around 10% sound output. Suspecting the preamp tubes, as all 12AX7A’s are shining only very dim compared to another BJr in side-by-side comparison.

    Wondering about replacement with (3) 12AX7 tubes (sans the “A” - and somewhat less expensive)?
     
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  2. stepvan

    stepvan Tele-Afflicted Silver Supporter

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    Should be fine
     
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  3. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    There's no difference. Anything after the main designator is just companies trying to be fancy. *Some* meant something back in the day, but not now.
     
  4. archetype

    archetype Fiend of Leo's

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    Dim means nothing. Only sound is important. Get some replacements to swap as a test. Any of the following will work fine:
    - 12AX7 = a 12AX7
    - 12AX7A = a 12AX7 designed for series or parallel heater wiring. Fine for your amp.
    - 7025 = a 12AX7 designed for lower self-noise. Fine for your amp.

    I'm in favor of NOS or used OS tubes. 12AX7 can be found at rational prices if you shop carefully. Any US, UK, EU, or Japanese tubes will sound fine and you don't need to buy some holy grail tubes for good tone. I've had good dealings with:

    audiotubes.com
    kcanostubes.com
     
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  5. Chiogtr4x

    Chiogtr4x Doctor of Teleocity

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    Have you tried subbing out the EL-84 power tubes with spares, in your trouble shooting?

    Just trying to eliminate variables.

    ( I've owned my BJ since 2000, and have had squeal/noise issues with a preamp tube a few times, and a 'flat' or lack of life sound with the power tubes, but never a loss of volume)
     
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  6. irie

    irie Tele-Holic

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    Just to add to what has already been said, I personally do not think there is a lot to be gained by running expensive vintage or NOS tubes in the blues junior. I really think you are best off by running new glass from a big brand like JJ's Grove tubes or the like. That is unless you believe there is something to be gained in terms of lifespan/durability with NOS tubes.

    In my own experience, my BJR is probably the least responsive amp I own (in terms of tonal change) to tube swaps. I have tried a lot of different tubes in mine, both new and old and have only heard nominal changes in the sound of the amp as a result of changing out tubes.
     
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  7. Pasta Player

    Pasta Player Tele-Meister

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    As much as I avoid pulling old tubes that are well “seated”… I swapped the 12AX7A tubes between the old and the newer BJr and the dim tubes then were still very dim in the older amp too. However, the newer amp returned once again to proper volume levels (und brightness) with the tubes from the older amp installed.

    So yup, the preamp tubes are the culprit here.

    *Have a spare set of EL 84’s from my older (2000) BJr that I changed out last year - but never considered testing them in this newer one. It seems to be working fine now.

    Thanks all!;)
     
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  8. Chiogtr4x

    Chiogtr4x Doctor of Teleocity

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    I think it was designed the way and I think the only 12AX7 to be concerned with in terms of gain shaping, is the one to the far right. The other two just have to be functional.
     
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  9. DrBGood

    DrBGood Tele-Holic

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    Regarding that first 12AX7: In my Traynor YCV20WR, I find the gain to be too gritty, square. So I swaped it for a 12AU7 and the gain became much creamier.
     
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  10. Pasta Player

    Pasta Player Tele-Meister

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    Odd…
    but the 2018 BJr had 3 different variants of 12AX7 tubes.

    V1 = GT ECC83-S
    V2 = GT 12AX7-R (Reverb???)
    V3 = GT 12AX7-C
    Pins on the 12AX7-C all look mottled, as if sand-blasted.

    Whereas mine was (1) plain GT 12AX7 and (2) GT 12AX7-WA
    Of course the newer BJr is a high-falutin Custom Tweed model.

    Thinking of ordering all Electro-Harmonix 12AX7-EH for mine.
    Thanks all… (more headroom supposedly - not so much gain).
    & put old EL84’s back as (1) new one has heat-ashed its’ paint.

    Might also try a 12AU7 in my V1 too, just to compare.
     
  11. zombiwoof

    zombiwoof Tele-Afflicted

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    -S: Slovakia (JJ)
    -R: Russia
    -C: China
    Al
     
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  12. Geo

    Geo Poster Extraordinaire

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  13. Andy B

    Andy B Friend of Leo's Silver Supporter

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    V1 TungSol RI 5751
    V2 TungSol RI 12AX7
    V3 Sovtek 12AX7LPS
    These are the preamp tubes I retube Jr’s with.
    Power tubes I like the TungSol or Sovtek EL84.
     
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  14. Pasta Player

    Pasta Player Tele-Meister

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    Many thanks to the nameless Craigslister that sold me three of these “unmarked” 12AX7B tubes yesterday for $15.00!
    Little did I realize that they are similar (if not identical) to the Electro-Harmonix EH-12AX7 preamp tubes that I’d intended to order.

    [Saved me $28.00 and the shipping wait.]

    2018 BJr w/ green board, Jensen & GTs versus…
    2001 BJr w/ cream board, Cannabis Rex & Chinese 12AX7

    Gunna be a little head-to-head & ABY action ‘round here.;)
    12AX7B.png
    *Combination Sweetwater & Tube Depot image above.
     
  15. Commodore 64

    Commodore 64 Friend of Leo's

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    LOL @ that graph. Sucker born every minute.

    It's a blues jr. It doesn't matter what the label is on any 12ax7 you put in there.
     
  16. zombiwoof

    zombiwoof Tele-Afflicted

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    Isn't the EH-12AX7 a Russian tube?. Also the Sovtek 12AX7WB previously mentioned is for sure a Russian tube. I know New Sensor distributes some Chinese tubes, but I'm not sure if they sell them under the EH label.
    Al
     
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  17. Dacious

    Dacious Poster Extraordinaire

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    The LPS is LP- long plate and S-spiral heater filament and therefore a little quieter. It's a longer plate tube with fairly high gain. I think it's personally the best modern V1 tube in Fender BF/SF clean amps, with very smooth and pleasant character.
     
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  18. DougM

    DougM Poster Extraordinaire

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    I've tried a lot of different 12AX7s in my Jolida EL84 25w/channel stereo integrated amp, and the EH, long plate Marshall branded Svetlana/Winged C (no longer made), and long plate EI (no longer made) were all good, but the LPS is my favorite, other than the extremely rare and expensive Raytheon with the long black plate.
    The new Tung Sol 12AX7 is also very highly praised by all. The EH that I have, that MB uses, is made in the Sovtek (Reflektor) factory, not in China. I generally prefer long plate ones, and I haven't tried the JJ one, their ECC803S, but their regular ECC83/12AX7 (with the frame grid) is a little too dark for my taste. I haven't tried the new Sovtek made long plate Mullard yet either.
     
    Last edited: Jan 30, 2021
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