Is the Internet Wrong? A Discussion About Maintenance and Modifications

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by gerrickreidenbach, Mar 20, 2020.

  1. d95err

    d95err Member

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    In general, fuses protect equipment from damage, not people. If you're being electrocuted, chances are lethal currents will pass through your body before the fuse pops.
     
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  2. d95err

    d95err Member

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    One thing often misunderstood with safety discussions is that electrical devices have to stay safe even under misuse scenarios, such as mechanical violence. For example, if the power cord (or socket) is ripped out of the chassis, the safety ground connection should be the last to go (hot and neutral should be ripped off first).
     
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  3. Pete Cage

    Pete Cage Member

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    Here are a couple of scenarios where a soldered ground (i.e.: lay the ground wire against the chassis and secure it with a puddle of solder) could melt.

    One is where the amp is plugged into an improperly-wired (and possibly over-voltage) outlet. I've seen this situation at big venues and temporary stages.

    The other is where the gear is subjected to an extremely large surge, like an indirect lightning strike on the building or nearby ground (plumbing, etc.)

    If the surge had sufficient current and melted the solder (which would most likely be the high-resistance point in the circuit) and the wire had any residual lifting tension (or even by its own weight,) it could move from the melted pool. And if all of the surge went through the ground connection, the amp/fuse might still be intact, and the amp might turn on and appear to work normally.

    Granted, these are extreme circumstances, but I've seen both causes actually take place. None of the affected gear had flat-soldered ground connections, though.
     
  4. zenas

    zenas Member

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    I won't drill a hole in a vintage amp, so if a transformer nut is the only place to put the ground that's where I'm putting it. Never know what kind of metal crimp connectors are made out of these days, I don't have a metallurgy lab, so I solder them.
     
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  5. pdf64

    pdf64 Member

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    But it's almost never the case that a transformer bolt is the only place available for the ground; my point is that the use of a fastener that goes through a transformer lamination stack is pretty much the worst possible choice for this purpose. Because the lamination stack is inherently compressible so the fastener will tend to slacken over time, and as the PT is generally the heaviest thing mounted to the chassis, those fasteners are already probably the most mechanically stressed on there.

    A competent operative would be unable to guarantee that crimped connection they made without the use of a calibrated, professional grade crimping tool and the correct crimp for that tool and the wire gauge used would be suitable for a safety critical application. Quite the opposite really, a connection made using a cheap crimping tool is fundamentally unsuitable for this purpose.
     
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  6. wall_of_sleep

    wall_of_sleep Member

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    After you're done discussing the chassis ground, I hope you are all updating every amp to insulated input jacks.

    It wouldn't hurt to make sure you're using a GFCI outlet as well.
     
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  7. gerrickreidenbach

    gerrickreidenbach Member

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    Why insulated?
     
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  8. Rockinrob86

    Rockinrob86 Member

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    a switchcraft style jack is a mechanical ground, whereas an insulated jack is only grounded through the soldered connection. he's making a joke.

    I do my grounds through a hole, near the power chord entrance. 6/32 bolt, a locking ring terminal and Kep Nut. I add a drop of loctite to the kep nut, crush the wire in the ring terminal, rough up the chassis with a file at the contact point and lock it down tight. Then I take my big stained glass iron and heat the chassis and the ring terminal and flow a nice blob of solder over the whole thing. So it is mechanically attached first and then soldered to the chassis.

    I have done the same thing on power transformer bolts, but I go back and forth on that. You could get it off if the transformer blew, but it would be annoying. But you don't have to drill an extra hole that way.
     
  9. gerrickreidenbach

    gerrickreidenbach Member

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    Of course, no need to run it into the ground...
     
  10. tapeup

    tapeup Butterscotch Supt. Member

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  11. gerrickreidenbach

    gerrickreidenbach Member

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    Well, what do you expect? I'm coming in at the ground floor here...
     
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  12. tapeup

    tapeup Butterscotch Supt. Member

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    At least you're well-grounded.
     
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  13. gerrickreidenbach

    gerrickreidenbach Member

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    I was once grounded for a year. I'll never forget that, just as my music was getting off the ground. It certainly brought me down to earth. Note to self: don't smoke on the school grounds.
     
    Last edited: Mar 28, 2020 at 3:00 AM
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