Rewinding an old Hoyer mandolin pickup ... the return of the dreaded air coil!

OilCityPickupsOilCityPickups Frets: 5150
This wound up on the work bench a few weeks ago ... so I thought I'd share!
It's an old (probably 1960s) Hoyer brand mandolin pickup ... and very dead. This is interesting as it pretty much apes the construction of early Hofner six string 'add on' pickups ... and was going to be equally a bitch to rewind.

Inside you see a ceramic bar magnet ... er well ... a well broken up one that was clearly like that from day one. With ceramics (and rubberised ceramic) it doesn't matter if the magnet is broken, so long as all the parts are held firmly in the right polarity.
There is a steel base plate that transfers the  magnetic field to the centre block that takes the four pole screws. In this case the pole screws really only hold the cover on and are not adjustable. Around the core you see a soft, squishy bag of wire that is the 'air coil'. With air coils there is no bobbin used, and the coil is wound around a removable former.
As there are no air coil formers made these days, we laser cut our own (see below) and pretty much have to do that for every different size of air coil we get to repair!

The time taken to CAD design and cut the former is a pain, as is making it so that tape can be passed through slots to secure the coil before removing it.
However the result is a working air coil pickup once more :-)

For those who missed how we make air coil formers ... take a look at our previous Burns Rewind thread 

Air coils do have a particular set of tonal characteristics ... and we are thinking of adding a couple of air coil designs to our lineup in future. 

Professional pickup winder, horse-testpilot and recovering Chocolate Hobnob addict.
Formerly TheGuitarWeasel ... Oil City Pickups  ... Oil City Blog

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Comments

  • ICBMICBM Frets: 49464
    It's really nice to see a pickup like this repaired properly, instead of some of the bodges I've seen... and might even have been responsible for one or two long ago :).

    Clue... the bobbins from the horrible 70s Japanese 'humbuckers' which are actually single coils will often fit into pickups like this (or at least the guitar versions).

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • I thought I'd share!
    Thank you. It is always useful and informative to get to see inside unusual pickups without having to dismantle one oneself.
    Be seeing you.
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  • NPPNPP Frets: 193

    Air coils do have a particular set of tonal characteristics ... 

    could you add a bit more detail for those of us who have never (at least knowingly) heard one? What kind of guitar, and what kind of tone or style, would they fit?

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  • OilCityPickupsOilCityPickups Frets: 5150
    tFB Trader
    NPP said:

    Air coils do have a particular set of tonal characteristics ... 

    could you add a bit more detail for those of us who have never (at least knowingly) heard one? What kind of guitar, and what kind of tone or style, would they fit?

    Essentially an air coil is super loosely wound ... to the point that if it's not potted, its a doughnut shaped bag of wire! it's like scatter winding taken to a massive extreme. They generally have very low capacitance and this leads to an open and very harmonically rich tone ... but also un-potted they can be very microphonic indeed. Burns potted their air coils solid in some sort of pitch like gloop to eliminate squeal ... and that - still very airy - tone can be heard on Brian May's red special.
    Air coils can have a biting, quite raunchy snarl when used at higher gain ... not super refined ... but great for blues, and all sorts of other genres where a punchy single coil tone is needed.
    Professional pickup winder, horse-testpilot and recovering Chocolate Hobnob addict.
    Formerly TheGuitarWeasel ... Oil City Pickups  ... Oil City Blog

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  • blobbblobb Frets: 1480
    Love these threads
    Feelin' Reelin' & Squeelin'
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  • NPPNPP Frets: 193
    NPP said:

    Air coils do have a particular set of tonal characteristics ... 

    could you add a bit more detail for those of us who have never (at least knowingly) heard one? What kind of guitar, and what kind of tone or style, would they fit?

    Essentially an air coil is super loosely wound ... to the point that if it's not potted, its a doughnut shaped bag of wire! it's like scatter winding taken to a massive extreme. They generally have very low capacitance and this leads to an open and very harmonically rich tone ... but also un-potted they can be very microphonic indeed. Burns potted their air coils solid in some sort of pitch like gloop to eliminate squeal ... and that - still very airy - tone can be heard on Brian May's red special.
    Air coils can have a biting, quite raunchy snarl when used at higher gain ... not super refined ... but great for blues, and all sorts of other genres where a punchy single coil tone is needed.
    sounds like just the thing for me then :) 

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