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Tweed Champ and Princeton, 560k grid to ground mod?

Discussion in 'Shock Brother's DIY Amps' started by Outlaws, Feb 27, 2021.

  1. Feb 27, 2021 #1
    Outlaws

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    A little after 11 minutes into that Terry suggests adding a 560k from the 6V6 grid pin 5 to ground. Says later champs did this. I don’t see any Fender schematics saying this.

    Also, that’s in parallel to the 220k? So he is suggesting dropping the 220k slightly to 158k~? Or he saying to up it to 560k? Sure looks like it’s in parallel as it seems the 220k is still there.
     
  2. Feb 27, 2021 #2
    tubeToaster

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    I don’t think he has ever built a 5f2a. He thinks it is a 5f1. I’ve never seen the tone cap placed on the board instead of between the volume and tone pots. And adding the 560k in parallel with 220k makes no since to me unless you want to kill a lot of your overdrive. And if he would place the circuit board more to the right ( input side ) he wouldn’t have a problem with the placement of the speaker jacks.
     
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  3. Feb 27, 2021 #3
    Outlaws

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    A 5f2a is a 5f1 with an extra pot and cap. They are virtually the same amp.
     
  4. Feb 27, 2021 #4
    Tom Kamphuys

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    beats me...
     
  5. Feb 27, 2021 #5
    tubeToaster

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    Yes I know.But he doesn’t seem to have ever built one with a tone control. I think he has some unconventional ideas.
     
  6. Feb 28, 2021 #6
    Outlaws

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  7. Feb 28, 2021 #7
    Tom Kamphuys

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    I did some more research, after reading Rob's post in the link above.
    Blocking distortion is an unwanted type of distortion that occurs when coupling caps charge as a result of grid current (because of large signals). There are two ways to minimize this: maximize the time to charge the capacitor and minimize the time to discharge the capacitor. Lowering the grid leak resistor reduces the discharge time constant and loads the previous stage down decreasing the signal. Other options, such as a grid stopper and lowering the coupling cap value, are also available.
     
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