Lamp on with power switch in off position!!??

Discussion in 'Shock Brother's DIY Amps' started by magic smoke, Aug 9, 2017.

  1. magic smoke

    magic smoke Tele-Meister

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    I played a new homebrew amp at a local pub tonight and experienced a puzzling phenomenon; The neon indicator was LIT with the power switch in the off position, and turned off when amp was switched on!!!??? When building and playing this amp in multiple tested and correctly wired environments everything works fine. When plugged into a different ac receptacle on the same stage at the pub, all worked as expected.

    I am now certain that the stage has faulty wiring at one of the outlets. I showed the engineer and they'll be testing all wiring on stage for safety.

    I’m concerned about the safety of my design.

    Are there any dangerous boo boos in the design of my power section? Please help me see how this circuit could create an inverse power lamp. Might the club have line voltage on the 3rd prong safety ground?

    FullSizeRender-4.jpg

    Notes:

    Schematic should show connection at neon/neutral of 3prong plug/chassis ground junction.
    Safety ground implemented but not drawn.

    See build thread here:
    http://www.tdpri.com/threads/5f1-from-antique-phono-extension-speaker.736481/
     
  2. Nickfl

    Nickfl Friend of Leo's

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    Are you saying that you have a connection between the neutral and the safety ground?
     
  3. magic smoke

    magic smoke Tele-Meister

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    Whoops, no. Third prong is connected to chassis only, has it's own dedicated ground point.
     
  4. Fiat_cc

    Fiat_cc Tele-Holic

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    What is the ground in your drawing from the neutral side of the neon?
     
  5. magic smoke

    magic smoke Tele-Meister

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    IMG_0022.jpg IMG_0029.jpg
     
  6. magic smoke

    magic smoke Tele-Meister

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    Neutral side of neon ties into the ground post for PT center tap / filter caps for power section

    IMG_0024.jpg
     
  7. Nickfl

    Nickfl Friend of Leo's

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    Why? I have never used a neon lamp, or any indicatior on the primary side of the PT, but it doesn't seem like it should be tied to ground. Is it connected to the neutral side of the PT and power cord, or just ground? Shouldn't it just run between hot and neutral?
     
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  8. Fiat_cc

    Fiat_cc Tele-Holic

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    I would move that to tie in with the neutral point where your PT primary and neutral from your mains power cord connect. You're essentially connecting your line voltage to ground with the current setup.

    Edit: Nickfl beat me to it.
     
  9. clintj

    clintj Friend of Leo's

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    Check out the schematic for the 18W Lite IIb. That shows the indicator in parallel with the PT primary, so it lights only when the switch is closed. The other easy option I see is install a double pole switch across hot and neutral, but I'd opt for the rewire option on the bulb.

    On the other hand, you do now have an impromptu outlet tester. :)
     
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  10. Wally

    Wally Telefied Ad Free Member

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    An outlet tester, which is less than $10, should be in every guitarist's bag. +1 with cLontJ's wiring suggestion .
     
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  11. magic smoke

    magic smoke Tele-Meister

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    Thanks guys!
     
  12. magic smoke

    magic smoke Tele-Meister

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    I checked the outlets with my tester today and there was an open ground on the bars extension strip. Now to rewire the amp...
     
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