P-90 poles and metal pickup covers touching

Discussion in 'Tele-Technical' started by ppg677, Apr 8, 2020.

  1. ppg677

    ppg677 Tele-Meister

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    I'm guessing P-90 poles that touch the grounded metal pickup covers is a non-starter?

    I measured ohms between the poles and grounded cover-- some are touching (very low ohms) and some are not (mega ohms).

    How the heck are metal pickup covers supposed to work?

    IMG_20200408_221905.jpg
     
  2. Deaf Eddie

    Deaf Eddie Friend of Leo's

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    I ASSUME that the reason for the metal cover is shielding, ergo, it should be grounded; the polepieces are threaded through the baseplate of the pickup which is also grounded. Seems like a non-issue to me.
     
  3. Speedy454

    Speedy454 Tele-Holic

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    The metal ccover should be soldered to the baseplate. The negative lead of the windings is very often soldered to the baseplate. You should not be concerned with a negative lead reading 0 ohms to the cover/baseplate/screws.

    What would be a 'non starter' is if the hot lead is shorted to the cover/baseplate/negative lead.
     
  4. TeleTucson

    TeleTucson Tele-Afflicted

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    Crossing Streams - Copy.png

    Don't worry ... its not as bad as crossing the streams in Ghostbusters. :eek::D

    The poles are not electrically connected to the windings, and their function is primarily directing magnetic fields, not providing pathways for electrical currents. Shorting a winding to ground at the wrong point is bad, but whether a pole is grounded or not won't make much difference at all.

    It's the same reason the metal cover doesn't kill things - the magnetic field passes right through the metal. However, covers can lead to some undesirable reduction in treble response if they are too conductive like plated brass. This is from eddy currents induced in the cover by the fluctuating magnetic field, and it is reduced quite a bit using lower conductivity metal for the covers like so-called "nickel silver" which actually has no silver in it.
     
    Last edited: Apr 9, 2020
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  5. ppg677

    ppg677 Tele-Meister

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    Makes sense. Thanks!
     
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  6. Lizzard

    Lizzard TDPRI Member

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    I wonder if they have the same effect wrt sound as with PAFs?

    I’m in the same place as the op, was thinking of switching to plastic for this reason.
     
  7. Dacious

    Dacious Poster Extraordinaire

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    There will be an effect with metal covers. More in the field to the sides, which has minimal impact on field projected by poles.
     
  8. Peegoo

    Peegoo Friend of Leo's

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    Metal covers can add capacitance to the coil, but for me that is not an issue because the the effect is minimal, and metal covers act as a shield to help block RF interference...which even humbucking operation cannot prevent.
     
  9. El Marin

    El Marin Tele-Afflicted

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    I added some brass covers to my P90s LP and had no issue. Some touched some didn't

    It sounds fine, so why bother?

    Well I pulled them out and left the plastic factory because brass was rusting and left my hand quite greenish after a gig

    [​IMG]

    That's the only pic I have...
     
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