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does a champ need grid stoppers

Discussion in 'Shock Brother's DIY Amps' started by Mongo Park, Oct 19, 2020.

  1. Mongo Park

    Mongo Park Tele-Holic

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    I have made a 5F2a, I have made a few and never had this problem.
    When turned to the max the amp has very bad distortion it even has a high pitched squeal l in there. I have a switch with standard negative feedback, off and on, which I have used before with no problem. With the negative feedback on it is not to bad, but not great, when I turn it off it is when it all goes to hell. So all this stuff is in their but just being suppressed by the negative feedback I am thinking. Changed the OT leads and the squeal was way worse, so put them back. Changed tubes not much help. Chopsticked around for no luck.
    Checked the bias with 10 watts coming from the 6V6. The plate voltage on the preamp plates are V1 140V, V2 148V.
    So what would cause this bad distortion and squeal. Do you think grid stoppers is the way to go.
    Cheers Ron
     
  2. gusfinley

    gusfinley Tele-Afflicted

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    I built 3 5F1s several years ago. ALL of them had some harsh non-musical distortion in them. One day I was researching a similar amplifier and someone mentioned inserting a 1.5K stopper at the input of the power tube. Within 15 minutes I added the 1.5K and they were all sounding great!

    Its worth a dime and a few minutes of your time....
     
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  3. Mongo Park

    Mongo Park Tele-Holic

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    Thanks I will try it out tomorrow
     
  4. Mongo Park

    Mongo Park Tele-Holic

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    It helped a lot so I am on the right path, thanks for taking the time to help me out.
     
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  5. James Knox

    James Knox Tele-Holic Silver Supporter

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    Interesting idea!
     
  6. James Knox

    James Knox Tele-Holic Silver Supporter

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    what did you like about it?

    what have you found out so far?

    why do you think this one is different?
     
  7. Mongo Park

    Mongo Park Tele-Holic

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    The grid stopper reduced the trouble down about %80. However it think, just me thinking out loud, it is masking the symptoms, but they are still in there somewhere. So I built a signal tracer in hopes of finding the source, have not used it yet. Meanwhile I chopsticks around more aggressively and found a unused wire from the output transformer coiled up in the bottom of the chassis may be the source of injecting crap into the guitar jack. The unused op transformer wires are in big coils at the bottom of the chassis. I thought they were out of the way but one coils into the neighbourhood of the input Jack. Moving it closer to the Jack seems to even bring in radio frequencies. I have to remove the chassis from the cab to see the sticker on the iron to tell which wire it is. I have not trimmed the wires and they are rather long.
    Update to follow, thanks for asking
     
  8. gusfinley

    gusfinley Tele-Afflicted

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    You could also apply some shielded wire to your low-signal inputs.

    I use shielded wire a lot these days because I get tired of chasing audio gremlins.
     
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  9. tubegeek

    tubegeek Friend of Leo's

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    https://www.tdpri.com/threads/rookie-build-champ-5f1.1036980/page-2#post-10074227
     
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  10. Mongo Park

    Mongo Park Tele-Holic

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    Shortened and tucked away the unused op transformer wires this removed all the unwanted bad noises.Squeal and all wen away, I removed the grid stopper and and it is still good. All I was left with was fairly loud buzz/hum I chopsticks around some more and shortened/re routed the negative feedback switch wires. The real culprit was the signal wire from the tone stack to the power tube. With the wire in a not so logical position and the hum left the amp. I have used shielded wire for the signal path but something was adding him anyways
    I need special glasses so I can see the electromagnetic fields that are produced around the wires and components, this would save a lot of time. Anybody know where I can get a pair.
    Cheers Ron.
     
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  11. chas.wahl

    chas.wahl Tele-Meister

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    Why does a Champ have a tone stack? If it does, it's no longer a Champ, but a 5F2-A, no? While on that topic, the 5F2-A doesn't have a grid stopper on the power tube, though Doug Hoffman's layout for it does, as well as the 470 ohm screen resistor.
     
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  12. elpico

    elpico Tele-Afflicted

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    [​IMG]
     
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  13. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Grid stoppers are always a good idea. They're not a substitute for clean lead dress though. :)
     
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  14. Mongo Park

    Mongo Park Tele-Holic

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    I think the screen resistor is a good if you are building it one more part for some extra safety. You can also use this to dial
    In your power tube as well Same goes for Rob’s 5Y3 diode protection. All part of a better build which makes it a little more than what you can buy. Course I am not force by the market to save a nickel or be forced out of business. Apples and oranges of course.
     
  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    It has been reported that Nikola Tesla performed feats with electrons which to this day have not been duplicated. The government squirreled away his papers. You won't be looking through any special glasses but when Apple cuts a deal there will be a phone app for that.

    :lol::lol::lol:
     
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  16. chas.wahl

    chas.wahl Tele-Meister

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    Doh! my bad! I should know better, since this was my first amplifier, back in 1965! Now when somebody says "Champ" I immediately think 5F1. Apologies.

     
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