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UBC pickups - in theory




Instead of having two coils of equal resistance, the coils of the UBC pickups are unequal, one coil having 50% of the resistance of the other. On a standard humbucker, coil tap results in half of the total winding of the pickup being cut, on a UBC pickup a third of the total winding is cut.
The statement that 'this prevents the 50% volume loss when in single coil mode' is misleading. On a purely linear scale, cutting 50% of the pickup out of circuit will equal a 50% reduction in output, however this does not actually equal anything like a 50% reduction in perceived volume (The human ear does not perceive volume linearly)

UBC pickups in practice

Several different kinds of pickups were fitted to guitars that according to the catalogues were supposed to have UBC pickups

1 - the first attempt at making UBC pickups was a spectacular failure. Instead of using two unequal coils, they used two equal coils, but they used the weaker (50% - about 3.5k) coil for both coils, resulting in nothing more than a standard , but extremely weak humbucker. All the ones I have seen have a resistance of about 6.5 to 7k. They can be identified by the plain steel plate on the back and the unusual (Philips screw style) ends on the pole pieces. 

2 - Presumably after they discovered what had gone wrong, but before the corrections could be made, they switched to their standard humbuckers. All the guitars I've seen like this have had MMK45s fitted, with hex headed pole pieces, which are also not UBC pickups.

3 - For guitars with the Magnaflux I pickup, unmarked pickups with the more normal hex pole pieces and a large plastic plate fitted underneath the pickup - I am not aware of any other Westone pickup that has that kind of design. These may be UBC pickups, or may not. On my November 85 Spectrum ST, they are not (The coils are equal, 6.5k total, 3.22 k coil tapped)
  - For guitars with the Magnaflux II pickup, the later pickups have hex pole pieces on one coil and a blade on the other (As in the picture at the top). The earliest example of this kind that I have seen is on my April 86 Spectrum FX. These pickups are also not UBC pickups, the coils are equal (11.2k total, 5.6 when coil tapped)

4- genuine UBC pickups. These may or may not actually exist, I have never yet come across one.

If you are considering buying a guitar that is supposed to be fitted with UBC pickups I strongly recommend asking the seller to either measure the coil resistances. If they are equal, it is not a UBC pickup. If the pickups have a total resistance of about 6.5k,I would personally not recommend buying the guitar without also replacing the pickups.