Unpleasant distortion in 6G2 Princeton

Discussion in 'Amp Tech Center' started by AlbertaGriff, Apr 11, 2021.

  1. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    I was going to ask - particularly with the screen grids.

    20210415_210629.jpg 20210415_210612.jpg
     
  2. ArcticWhite

    ArcticWhite Tele-Afflicted

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    Can't hurt to try!
     
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  3. theprofessor

    theprofessor Poster Extraordinaire

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    Yes, I would definitely replace those screen grid resistors. Get some high-wattage ones (2 or 3W). Metal oxide or cement or something like that, preferably. Hang them off the side even more so that they get hit with less heat than when they're close to the tube socket.
     
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  4. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    Yeah they look almost integrated into the pins.
     
  5. Bob Arbogast

    Bob Arbogast Tele-Afflicted Silver Supporter

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    Uhh, those are 1.5k grid-stoppers on the control grids
     
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  6. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    Ah, my mistake. My terminology isn't great.
     
  7. theprofessor

    theprofessor Poster Extraordinaire

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    Yes, sorry to have perpetuated the error myself.
     
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  8. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    I'm probably going to try a few more things to correct this issue this weekend.

    However, I came across this video and noted that the sound I hear in my amp is also quite prominent in this amp, click ahead to 2:41 to where intensity is maxed:



    I also found this older TDPRI thread where a member built a 6G3 with some unpleasant distortion on the trem:

    https://www.tdpri.com/threads/6g3-bias-tremolo-distortion-problem.1036803/

    That member fixed it by swapping out a 220k resistor before the 0.1uf cap ahead of the intensity pot for a 470k.

    Things I plan to try:
    -the above resistor swap
    -swapping out grid-stoppers on the power tubes

    If neither of those two have any impact, I'll try the following as a last resort:
    -swapping other resistors in the trem circuit
    -swapping out the 0.1uf caps

    Hopefully one of these has some effect on at least lessening the distorted tone I hear.
     
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  9. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    Nothing helped! Still haven't tried the 0.1uf caps but I'm not optimistic. Starting to think it's a little inherent to the circuit, and emphasized by the current speaker.

    So I'm going to try a swap...

    I pulled the '67 CTS alnico and...

    20210423_161109.jpg

    I wonder how much all this dust is impacting the sound.
     
  10. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    Deleted post.
     

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  11. ArcticWhite

    ArcticWhite Tele-Afflicted

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    Those coupling caps are how old now?
     
  12. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    Only 59 years. I've tried swapping out all of them except the 0.1s in the trem and PI circuits.
     
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  13. theprofessor

    theprofessor Poster Extraordinaire

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    Man, that speaker was nasty! Can't hurt to clean it. Let us know what you find once you swap out the .1uF caps in the tremolo and phase inverter circuits. I know this must be driving you crazy. I hope you're able to find the culprit.
     
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  14. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    After seeing that YouTube video of that other amp doing it too, I feel a bit better about the sound just being part of the amp. It's almost like the intensity knob goes TOO high...

    But I'm sure at some point I'll try the 0.1 caps one by one haha.
     
  15. ArcticWhite

    ArcticWhite Tele-Afflicted

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    What if two of them are bad?
    I'd do the PI, and then the trem.
     
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  16. AlbertaGriff

    AlbertaGriff Tele-Afflicted

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    Good point. I guess I just thought if one was replaced it would at least sound "better" or different, even if not completely fixed.

    The amp is sounding pretty great outside of this trem issue. Makes me thinking the PI is fine, but admittedly I can't say that for sure.
     
  17. ArcticWhite

    ArcticWhite Tele-Afflicted

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    Capacitors in the tremolo circuit are not in the signal path so you can use anything there. They won't affect your tone in the slightest.
     
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