Jef Brown 5e3 Grid Mod.

Discussion in 'Shock Brother's DIY Amps' started by Tele Slacker, May 10, 2021.

  1. Tele Slacker

    Tele Slacker Tele-Meister

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    Searched a little on this... sorry if I missed a previous discussion. I was listening the The Fretboard Journal's wonderful podcast "The Truth About Vintage Amps" and Jason and Skip were interviewing Jef Brown (blog linked here). No affiliation (other than being a patreon supporter for TAVA). On this episode of the podcast, they revisited a previous discussion about connecting a 3.3MOhm resistor from the last power mode to the grid of the the phase inverter. To hear the story, all of this was serendipity... i.e. "dumb luck". But the results was pleasing to the amp owner, and some other good ears (I won't rehash the story, you can check it out if interested).

    Anyone have any experience doing this?
    upload_2021-5-10_15-10-24.png
    I don't have a 3.3MOhm resistor laying around, but am considering ordering a few (well... at least one) to give it a whirl on a homemade clone. Just wondering if someone here has already broken ground?
     
  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Not quite the same but the Dumble Tweedle Dee local NFB is similar. It has the 3M3 resistor in series with a .0022uF cap on the PI from the plate to control grid.
     
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  3. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    Is it some kind of fixed bias?
     
  4. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    Other than a 3M3 resistor near a phase splitter, I don't see any similarities.
     
  5. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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  6. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The 3.3M forms a voltage divider with the phase inverter grid leak to set a fixed bias. I'm not a fan.
     
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  7. Tele Slacker

    Tele Slacker Tele-Meister

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    Appreciate the feedback. Ordered some 3.3Mohm resistors…. Might try it on a switch… easy enough… that’s what clones are made for, no?
     
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  8. NTC

    NTC Tele-Holic

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  9. Tele Slacker

    Tele Slacker Tele-Meister

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    Rob, were you ‘not a fan’ based on sound, or potential concerns with the circuit (longevity, etc.)?
     
  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Just not a fan of the tone change.
     
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