Marshall 2203 JMP Master Model preamp tube question...

Discussion in 'Marshall Amps' started by Fret-Shredder, Nov 15, 2019.

  1. Fret-Shredder

    Fret-Shredder Member

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    Hey guys... I tried searching first but couldn't find my answer. I know someone here knows for sure. The amp is from 1977. I want to try some 12AX7s I have in this amp and need to know which of the three should I try if I want to effect the distortion the most. More gain. I dont even know which is V1 , V2 or V3. Thank you for any help. Cheers guys.

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    Last edited: Nov 15, 2019
  2. South Park

    South Park Well-Known Member

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    All three make distortion. The first is the gain .The second inverts the signal clipping .the third drives the drivers. It’s the combination of guitar amp speakers that gives you the sound you want
     
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  3. Fret-Shredder

    Fret-Shredder Member

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    Thanks for the reply. I have a Bugle Boy Amperex from Holland 12AX7 and was wondering which position I should try it in.
     
  4. South Park

    South Park Well-Known Member

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    They all have the same gain rotate the tubes and see how it sounds.
     
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  5. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    Bugle Boy is a really good tube.
    And we can't get it anymore.
    Just try it in V1 or V2 or V3 and see where it sounds the best.

    No, they do not all have the same gain....they are all different.
     
  6. EADGBE

    EADGBE Well-Known Member

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    Try it in the first preamp tube position at the far left. That is V1.
     
  7. Matthews Guitars

    Matthews Guitars Well-Known Member

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    The preamp tube closest to the input jack is V1 and it's the most important one for gain and distortion.

    I have one Amperex Bugle Boy tube in my stash and its sound is too clean and clinical. Very "high fidelity", without any really desirable tone generating characteristics. Frankly it's a boring sounding tube.

    V2 is the cathode follower tube. On that amp, don't use a Russian made tube in V2. They can't handle the high grid voltage that is applied in a cathode follower stage.

    V3 is the phase inverter. It determines the level of output stage drive that is fed to the power tubes. It needs to be a tube that has both sections well
    matched to each other for gain. If the two halves of the tube are not well matched, hum can result.

    If you're looking for more distortion, try different 12AX7, 7025, or ECC83 tubes in V1. Changing tubes in V2 and V3 isn't going to do much if anything to change the amount of distortion coming out of the preamp.
     
    Last edited: Nov 16, 2019
  8. Trelwheen

    Trelwheen Well-Known Member

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    I've got RFT ecc83s (12ax7) in V1 and V3, and a current production Shuguang 12ax7 in V2 of my '78 2203. This makes a pretty good combo if you're looking for a good amount of gain in the preamp.
     
    Last edited: Nov 16, 2019
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  9. eastwood6

    eastwood6 Well-Known Member

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    I’m pretty sure the RFTs were the pre-amp tubes Marshall used when the JMP amps were new. They sound great, very organic and crunchy without being over the top. Worked great in the 2104 combo I used to have.
     
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  10. Matthews Guitars

    Matthews Guitars Well-Known Member

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    This is exactly what you should not do. The Sovtek (Russian made) tube has a spiral filament and it isn't rated to handle the voltages placed across the grid and plate in the cathode follower, which is V2 on a 2203.

    The exception to the rule are the Sovtek 12AX7WA and 12AX7WB. That'll be addressed later down this post.

    No Russian tubes should be installed in V2 on a vintage Marshall except as noted below. That means the following brands: Sovtek and the reissues under the names Mullard, Tung-Sol, EH/Electro-Harmonix.

    "Spiral filament 12AX7 tubes have problems in cathode follower circuits due to the fact that most cathode follower circuits in guitar amplifiers exceed the maximum cathode to heater rating of 100 volts. The Svetlana 12AX7 does not have a spiral filament, so you should not have problems. The most rugged 12AX7 types for cathode follower service are the Sovtek 12AX7WA and WB."
     
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  11. Trelwheen

    Trelwheen Well-Known Member

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    Wow I thought it was a Sovtek but it's got flat short plates. I'll take a pic later and send it to you. I'll pull it if you tell me that's what it is
     
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  12. Matthews Guitars

    Matthews Guitars Well-Known Member

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  13. Trelwheen

    Trelwheen Well-Known Member

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  14. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Far as I know, Chinese 12AX7s are fine in V2. Some have very high gain figures, which is great if the noise figure is low to go along with it.

    Chinese 12AX7s are good to go, usually. But Chinese power tubes of some types are not to be trusted and have cost a lot of people a transformer.
     
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  15. Neil Skene

    Neil Skene Well-Known Member

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    This is my 1977 JMP with an old Sylvania 12AX7 in V1. I always think it needs more gain until I hear it recorded with drums.
    The volume was rolled back to 4 on my Fender with a Seymoure Duncan full Shred pickup. Unless you are after Metal type gain then I think all 800's need a push in the front.

     
  16. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

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    Your amp sounds just as a Marshall should..
     
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