Grab a seat kids, while ol' Uncle Tookay relates his Rick-o-ramblings...
The first 4001's built in late '62/ early 63 had toasters and horseshoes, wound with #54 gauge wire. The horseshoes used 3/8" magnet slugs, and the shoes were actually magnetic. This setup ran from 1963 to 1972, when the first "Hi-Gain" / button-tops appeared, mounted on an aluminum plate for height adjustment. The original horseshoe was officially discontinued by January 1973, although there are some rare examples of horseshoes showing up on 4001's as late as April 73. The button-top in the neck ran consecutively with the toaster in 1973, until Rick ran out of the toasters. There are examples of toasters in bases as late as September 73. There are also some uber-rare examples of bridge button-tops with slot adjustable pole pieces around late 72, around the same time as the 21 fret 4001.
By late 73, Rick ran out of the toasters, and by early 1974, the bridge button-top was mounted on a plastic plate. This arrangement remained pretty much unchanged until Rick began winding the pickups to 11k from 7.5 k in 2001 (I expect to be corrected on that date).
The horseshoe pickups being made have the same slugs and resistance, but the shoes are more for decoration- and are removable if you're careful- than having any function. i have heard tell that the horseshoes that Jason Lollar made prior to being shut down by the Hall's legal sharks, were also fully magnetic.
Does the magnetism of the shoes make a difference? Well, after playing a VERY famous 65 4001s, and then playing the re-issue version, there is a definite difference in response. I put a re-sh, back when Rick was actually selling the horseshoes as parts, into my 73 4001FG, and it was close, but not quite 'IT'. Sure sounded good through a big Ampeg tube/ 810 rig, tho'.
