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Thread: grid stoppers and scren resisters?

  1. #1
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    grid stoppers and scren resisters?

    I have read some people put them on amps that never had them like stating that on princeton with the 1k dropper if the screen fails on the 6V6 then the 1k dropper with save the amp and that grid resisters 1.5K are only for RF interference.

    I put the 470 ohm screen resisters on both my builds the SF champ build and the P-P 6G2/5E3 and also put the 1.5k grid resisters on both. any harm in doing this? Both fender stock amps and the 5E3 had the 1.5k grid stoppers but none had the 470ohm screen resisters The SF champ had neither.

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  2. #2
    Senior Member stormbringer's Avatar
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    Many folks (Kevin O'Connor for one) advise that the screen R should be at least 1k. 5 watts would be a good safe rating. R Aiken recommends metal oxide, but either way it should be flame proof.

    Forget the low values used by Fender.

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  3. #3
    Old Timer soundguruman's Avatar
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    Well, the resistors do act as a fuse if the tube shorts. When the resistor burns, it is protecting the rest of the amp, so to speak.
    The resistors are going to limit current, if for no other reason, the resistor can only take so much before burning.
    And it has been common to fuse (even) the HT to the output transformer.
    The resistors you added are not hurting the amp, but in some way you are changing the sound characteristics.
    If you add a 470 ohm resistor to the screen, you are slightly changing the ideal bias point of the tube. But not much.
    If you lower the screen voltage, you are making the plate more sensitive, to some measurable degree. But I don't think it's a lot.
    You may not be able to tell, to the human ear, that the parts have been added. But I can see the reasoning behind wanting to make the circuit more protective.

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