A really big sounding pickup. Single coil tone with focus yet a little knarley around the edges. Very much like a P90 type pickup but with a much bigger personality.
These were originally found in Valco® and Supro® guitars of the late 50's and through the 60's. The originals were of a dimension that did not allow them to easily fit into other guitars. This made them not so popular to retrofit into guitars other than the original guitar.
They will now fit into any guitar that can hold a humbucker. They are made to the original specs. Same size coil, magnets and magnet wire. It's tight but it all just fits if carefully made.
It's a tone that has been lost or forgotten but I think it's a tone that needs to be added back to the tonal palate for musicians.