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Thread: Preamp tubes marshall jtm60

  1. #1
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    Default Preamp tubes marshall jtm60

    Hi there!

    I have a Marshall JTM60 for a few years now and it's great. But recently I'm experimenting with some tubes swapping.

    It now has 2 JJ power tubes
    V4, v3, v2 are also JJ(12ax7) and V1 is a Tung-Sol 12ax7.

    I've ordered a Genalex Gold Lion 12ax7 for the V1 position because I'm curious what the real difference is and if the stories are true that it's one of those 'best' tubes....

    But.. I want to swap the tung-sol and put the gold lion in V1. What does v2 v3 and v4 exactly do? I don't use the gain channel.. Only the clean. Does v2 and v3 also affect the clean sound?

    Thanks!

    Marco
    (Netherlands)

  2. #2
    Tone Member Bronze Buzzard's Avatar
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    Default Re: Preamp tubes marshall jtm60

    I'll give this one a try.

    Preamp tubes stack. Each stage, which is usually 2 per preamp tube, has a gain factor. These gain factors stack for each stage. All pre tubes have a different gain factor, and V1 tends to shape your distortion type the most.

    There is more to it depending on amp circuit and how the amp is layed out, but yes. V2 and V3 can have an impact on overall tone and feel. I'll have look at the JTM circuit, but something tells me V1 is not cascading.

    V1 can be split or cascading, and V3 tends to be a PI. V3 can be tricky depending on amp design.

    Play with different types of tubes as well in each position. 12au7s, 12ay7s, 12at7s, and in any combination. Playing in the dirt and learning for yourself is part of the fun.
    Last edited by Bronze Buzzard; 05-24-2020 at 01:19 PM.

  3. #3
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    Default Re: Preamp tubes marshall jtm60

    Quote Originally Posted by Bronze Buzzard View Post
    I'll give this one a try.

    Preamp tubes stack. Each stage, which is usually 2 per preamp tube, has a gain factor. These gain factors stack for each stage. All pre tubes have a different gain factor, and V1 tends to shape your distortion type the most.

    There is more to it depending on amp circuit and how the amp is layed out, but yes. V2 and V3 can have an impact on overall tone and feel. I'll have look at the JTM circuit, but something tells me V1 is not cascading.

    V1 can be split or cascading, and V3 tends to be a PI. V3 can be tricky depending on amp design.

    Play with different types of tubes as well in each position. 12au7s, 12ay7s, 12at7s, and in any combination. Playing in the dirt and learning for yourself is part of the fun.
    I have 4 preamp tubes.. So I quess V4 should be PI?

  4. #4
    Super Moderator Simon_F's Avatar
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    Default Re: Preamp tubes marshall jtm60

    Quote Originally Posted by dudiluty View Post
    I have 4 preamp tubes.. So I quess V4 should be PI?
    Yes, the 12AX7 closest to the power tubes is the phase inverter.

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