6100 sounds great, when it isn't crackling

Discussion in 'Marshall Amps' started by rsjd41, Sep 20, 2021.

  1. rsjd41

    rsjd41 Member

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    So I've had this 6100 for a number of years. It still sounds very good but as most owners know, Marshall has a problem with noisy pots. I have to rectify that on all of my Marshall's again and again despite covering them, etc.

    But now the 6100 has developed a new problem. Every so often it breaks into a cute little crackling sound. It typically is worst in the clean channel but it also seems to bleed into the lead channel as well. It really is ridiculous. If someone was using this for a gig? I don't any longer but it would be really tough. I have noticed that tapping around the chassis when it is doing this can lead to hearing the tapping feeding through the amp. I guess it might be a microphonic tube but I thought I would see if anyone else has experienced this before I start tearing it apart. I already have to work on my 8240. One at a time for God's sake. Thanks...
     
  2. anitoli

    anitoli Well-Known Member Gold Supporting Member

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    How long has it been since it's been retubed?
     
  3. PelliX

    PelliX Well-Known Member

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    Tap the valves, connectors and pots. Often, those problems are simply to identify and not too much work to fix.
     
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  4. rsjd41

    rsjd41 Member

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    Yeah, I need to find my schematic. Make some room but this is of lesser urgency than the Vavlestate I have to work on.
     
  5. rsjd41

    rsjd41 Member

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    It's been a little while but I had it looked at last fall and they seemed to be fine. I more suspect something in the preamp but I have to find my schematics. And some room.
     
  6. rsjd41

    rsjd41 Member

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    Yeah, as I stated in another reply, I need to find my schematics. I'm just trying to find out if anyone else has seen the same problem. The pots always need help. I'm not sure what they were thinking when they built these. Not the only Marshall I have pot problems with either.
     
  7. Jethro Rocker

    Jethro Rocker Well-Known Member

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    Try V1 and V2 or PI tube. No need for schematics for that. Possibly still a cruddy pot too. Or power tubes. I have had that issue before and all of those were culprits at one point or another, same symptoms.
     
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  8. rsjd41

    rsjd41 Member

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    It's interesting that you mention the phase inverter as it seems to be most prone to the tapping effect. Thanks.
     
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  9. Jethro Rocker

    Jethro Rocker Well-Known Member

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    Because it is present on clean plus other channels. V1 affects only the clean channel. I have had power tubes that crackled till amp was warm. Then was fine. One tube was goofy.
     
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  10. anitoli

    anitoli Well-Known Member Gold Supporting Member

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    All Schematics are on my site:

    http://home.myfairpoint.net/vze1u14s/petes6100midisupportservice

    Not sure why you are having issues with the pots, out of all 4 of my 6100's the ONLY pot ever needing to be changed was the volume pot. Too many rotations. And out of the numerous amps sent to me the volume pot is #1 on the replacement list.
     
  11. rsjd41

    rsjd41 Member

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    I don't know. I just know it does. And the volume pot is definitely the worst. Thanks a lot for the link to the schematics. I appreciate it very much.
     
  12. pedecamp

    pedecamp Well-Known Member

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    I would start by cleaning the tube sockets with Deoxit and reseating the tubes. Clean all the pots and inputs with Deoxit at the same time as well. :yesway:
     
  13. rsjd41

    rsjd41 Member

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    Yeah, I happened to pull the PI tube out earlier. It went through the crackling once but then was fine for the rest of the afternoon.
     
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  14. pedecamp

    pedecamp Well-Known Member

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    Pull them all out, spray a shot of Deoxit on the tube pins and insert and pull out the tube several times in the socket to clean it, you may find better contact eliminates the problem, clean the pots and inputs too! :yesway:
     
  15. rsjd41

    rsjd41 Member

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    Of course. I understand that, I was just mentioning that pulling and replacing the tube appeared to help so it could well signify that just doing that removed some corrosion. I have a can of Deoxit and had already planned on cleaning the pots. So I'll clean the sockets and see how that does. Thanks.
     
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  16. rsjd41

    rsjd41 Member

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    By the way, I failed to mention that turning standby back off then on again sometimes gets rid of it. Also, I was messing with the damping switch, from auto to high to low and back and that caused it to go away as well. Any thoughts? I'll probably deal with the sockets this weekend, just thought I'd see what you think of this. Thanks...
     
  17. Matthews Guitars

    Matthews Guitars Well-Known Member

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    A 6100 is old enough to possibly be due for a cap job. They usually came with LCRs if I'm not mistaken, and LCRs just don't have the lifespan of the older Dalys. Crackling can certainly be a symptom of bad capacitors.

    They've got to be 30 years old. If they're LCRs, they're due. Get that done and I bet the crackling goes away.
     
  18. pedecamp

    pedecamp Well-Known Member

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    Im no tech but that sounds like you may have a cold solder joint somewhere. Best bet is take it to a competent tech and explain all this to them. :yesway:
     
  19. anitoli

    anitoli Well-Known Member Gold Supporting Member

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    They had anything and everything for caps thrown in these.
     
  20. rsjd41

    rsjd41 Member

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    I am a competent tech. I think you're probably correct. I will hopefully get around to working on it this weekend. I'm just looking to see if anyone else has seen this problem before I spend too a lot of time screwing around with it. One thing that made me consider the solder joint? Both the PI tube AND the damping switch are like right in the center of the chassis. I just have to be more careful these days. The plate voltages are more than sufficient to trigger the defibrillator portion of my pacemaker. And that would be no fun....
     
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