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Serious issue with a ‘70 fender dual showman reberb

Discussion in 'Amp Tech Center' started by Jeremyhasaproblem, Sep 4, 2020.

  1. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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    The amp works and sounds great, but after 3-4 minutes of playing it starts shocking the player through the strings of the guitar(and only in this manner). None of the cords, connectors, switches, pots or jacks exhibit that quality(they don’t shock you). I can do basic electrical soldering and simple electrical work, but would like to see if someone more experienced has any idea why something like this would happen? Especially since this amp has a ground in the cord and also in the circutry.
     
  2. Fretting out

    Fretting out Poster Extraordinaire

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    Is it all guitars or just one?
     
  3. stantheman

    stantheman Doctor of Teleocity

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    Just a hunch - it sounds like the guitar ground solder broke apart. Someone else will know for sure.
     
  4. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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    It does this on all guitars that i plug in, but the guitars i have all have passive pickups(no idea if that matters at all). I should also mention a have a second dual showman reverb(i think it’s a ‘68) that i can potentially scavenge parts off of if i have to. That amp does not shock the user, but it also makes no sound.
     
  5. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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    I will try to post a picture of the board in a couple minutes, my phone is being stupid at the moment.
     
  6. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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    upload_2020-9-4_21-29-40.jpeg
    is there any way that this switch would matter in that way?
    Also, i may be the dumbest person alive...
     
  7. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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    backside of the amp w/cover removed.
     
  8. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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    ^^*
     

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  9. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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    Okay it’s clearly going to take a while to get the board out, somebody was messing around with this thing before and they were rather messy about it.
     

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  10. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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    upload_2020-9-4_22-11-27.jpeg
    upload_2020-9-4_22-11-44.jpeg
    upload_2020-9-4_22-12-3.jpeg
    upload_2020-9-4_22-12-18.jpeg
    pics of the “circut board” , to me it just looks dirty and like it has been sloppily repaired, but you guys definitely would know better than me. I hope one of you can see something that doesn’t look quite right to you so that i can address it. As i said i can do basic electrical work but know very little about these specific amplifiers other than the fact that they sound incredible.
     
  11. Fretting out

    Fretting out Poster Extraordinaire

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    Honestly I have no idea about amps, I was thinking something simple may have happened, maybe the guitars bridge wasn’t grounded

    Since it’s happening on more than one guitar that should rule that out
     
  12. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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  13. glenlivet

    glenlivet Tele-Holic

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    123.png

    I'm no expert on that particular amp (or anything else really)...but that sure looks like 2 wire power to me?
    If your plug has 3 prongs on it....then somebody spliced the cord (and left the ground unconnected).
    I could be way off base, but it looks to me like you have no chassis ground.
     
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  14. tubegeek

    tubegeek Friend of Leo's

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    Does the amp have a 3-prong cord or only 2?
     
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  15. brown2bob

    brown2bob TDPRI Member

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    I only see two wires on what appears to be the power input. This would support that the amp is not really earth grounded. There should be three wires, white=neutral, black=hot, and green=chassis ground.
     
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  16. Jeremyhasaproblem

    Jeremyhasaproblem TDPRI Member

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    Yes it is a 3 prong, yes it is spliced after the board. My apologies i could have sworn this was the one that we added a ground at the board to, it must be the ‘68 we erroneously added a “chassis ground” to. I’ll have to clip and redo this one properly. Thank you so much.
     
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  17. tubegeek

    tubegeek Friend of Leo's

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    Be safe. Rock on.
     
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  18. hepular

    hepular Tele-Meister

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    So, in a case like this, what would be the best procedure? drill a hole in the chassis & star-fangle washer, sheet-metal-screw & solder the ground wire or ground to that transformer bolt? or just wrassle the 100w iron in and solder to chassis?
     
  19. tubegeek

    tubegeek Friend of Leo's

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    For ground: dedicated bolt with lock washer, with a crimped-on ring terminal to the green wire. Ground wire longer than (more slack than) neutral and hot. Go in through the original hole, if possible, and use a standard D shape grommet to strain-relieve the cord. This is why we salvage 3 wire cords & D grommets from stuff people throw out!

    Soldering to the chassis is SO last century!
     
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  20. BobbyZ

    BobbyZ Doctor of Teleocity

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    The guitar's "ground" is the amp's chassis "ground". The shield in the instrument cable ties those together. I used "ground" because sometimes there's voltage on the chassis.
    That's why a properly installed grounded cord plugged into a properly wired outlet is such a nice thing to have.
     
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