4210: Boost channel much less volume than clean channel

Discussion in 'The Workbench' started by R.H, Nov 10, 2019.

  1. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    These are Fender authorized service centers the techs are qualified for tube amps. Should be knowledgeable people.
     
  2. RickyLee

    RickyLee Well-Known Member VIP Member

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    Do you know if you have the first preamp design or the later preamp design? 1983 is primarily the cut off when Marshall did the new design. But I have seen a few early 1984 models, mainly 4210's, have that first design.

    If you do end up going to a shop, please post what the problem was.
     
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  3. Gunner64

    Gunner64 Well-Known Member Premium Member

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    My 2205 was weak on the boost channel as well, and the normal channels controls had an effect on the boost channel. My problem stemmed from a broken solder joint where the pots mount to the pcb. I reflowed all of them and amp worked perfect after that. I'm not sure which one was the culprit as I reflowed them all, but that was my experience with mine with the same condition.
     
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  4. R.H

    R.H New Member Premium Member

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    Bought several new JJs and spent the time to be more methodical with volume and tone settings.

    Wound up replacing the PI with a known-to-be-balanced JJ, and replaced V2. That seems to have taken care of the issue. If the two channels are unbalanced now, I sure can't tell by ear.

    Thanks very much everybody.
     
  5. RickyLee

    RickyLee Well-Known Member VIP Member

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    If you pull out V2, then run the amp, you can verify which version preamp you have. If you lose the Normal channel, then you have the later design '83/'84 - '90. If you lose the Boost channel, then you have the first early design '82 - '83/'84.

    On the later design, V2 is Normal channel only. I like running lower gain tubes there or even a 12AY7 to give that channel a more clean sound.
     
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  6. R.H

    R.H New Member Premium Member

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    Pulling V2, I lose the Normal channel and the Boost channel volume seems very reduced.

    EDIT: Maybe the tiny bit of Boost channel I hear when pulling V2 is that channel bleedover I hear was an issue early on with these amps?
     
    Last edited: Nov 17, 2019
  7. RickyLee

    RickyLee Well-Known Member VIP Member

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    Pulling V2 and losing the Normal channel means you have the later design. But then it should not affect the Boost channel. But . . if you have bleedover of Normal into Boost, then that could explain why the volume dropped a bit on the Boost channel.

    Thr bleedover you can diagnose by playing around withe controls to find the interaction between channels.
     
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