PT Primary Switching/Fusing

Discussion in 'Shock Brother's DIY Amps' started by muswell_hillbilly, May 20, 2019.

  1. muswell_hillbilly

    muswell_hillbilly Tele-Meister

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    I'm still new to this amp-building obsession, so I apologize in advance if I'm walking down a well-worn road...

    Regarding PT primary switching/fusing, shouldn't both be on the "hot" conductor? On a different thread, I found myself reviewing a Mojotone 5F1 schematic, and found this:

    upload_2019-5-20_16-11-41.png

    Then I looked around a bit more and found this on their 5F2A schematic:

    upload_2019-5-20_16-15-48.png

    Aren't these both wrong? Shouldn't the switching/fusing be on the "hot" conductor? (I really hope I'm not poking some hornet's nest with this question)
     
    Last edited: May 20, 2019
  2. muswell_hillbilly

    muswell_hillbilly Tele-Meister

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    Here's my thinking (which may be completely wrong): in both cases above, the return path is interrupted, but the source remains (potentially) active (no pun intended).

    With an active source looking for a return path, I'm a potential candidate, however remotely.

    If the source path is interrupted, the return path is looking for a source, and I believe I'm a poor candidate (been a long time since my wife called my "hot")...
     
    Last edited: May 20, 2019
  3. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    wf55.jpg

    Why not interrupt both and be certain?. The switches don't cost much, and it's better than being zapped. I'm fairly certain it's a requirement in Europe, and it makes sense to me.
     
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  4. Wally

    Wally Telefied Ad Free Member

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    Switch both hot and neutral...run the hot through the fuse as VintageSG shows us.
     
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  5. Nickfl

    Nickfl Tele-Afflicted

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    As mentioned it ideally should be both, pretty sure UL listing requires it too. But if you are right that if you're doing a spst it should definitely be on the hot side.

    There is some argument over the order of the fuse and switch too. I do mine power cord hot -> fuse -> switch -> PT. The theory is that way if the fuse blows it isolates as much of the circuit as possible from the mains power.
     
  6. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Yes, those are both wrong. Every time we mention this to Mojoton they say "we try and keep things vintage correct." Yeah, well.............

    Modern "real" companies break both hot and neutral, as I believe that is required in Europe and elsewhere. American stuff you'll see one of the following:

    live side >> fuse >> switch >> one side of PT. Neutral to other side of PT
    or
    live side >> switch >> fuse >> one side of PT. Neutral to other side of PT

    People argue it both ways, fuse or switch first, all the time.
     
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  7. muswell_hillbilly

    muswell_hillbilly Tele-Meister

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    Hmm - bloodletting was once a "cure" ;)
     
  8. Finck

    Finck Tele-Afflicted

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    Break hot and neutral is always safer, because there are faulty electrical installations in what a potential exists between neutral and ground.

    The fuse always goes in the hot wire, because in the case of a short circuit, the current will probably returns through ground wire, so a fuse in the neutral wire will be useless.
     
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  9. FenderLover

    FenderLover Friend of Leo's

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    That 'vintage correct' crap has really run its course. I wish people would accept that many things have been learned in the last lifetime.

    If vintage correct is so important, do they also wire their heaters with one wire? If not, why? It takes conviction to be wrong and stand by it.
     
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