The celluloid bobbin from this ES-300 style pickup from a 1940 Gibson EH-150 was brittle, cracked, and disintegrating in places, the windings were broken, and the magnets were missing. There was really no choice but to completely reconstruct the pickup but it provided an opportunity to look inside a rare pickup. The construction is very similar to a P-90 but with a toothed metal core that extends up through the coil. I was not able to find much information about this pickup so I had to go intuition.
I replaced all of the celluloid, except the wraparound covering that was still in good condition, rewound (42 PE wire, 8750 turns, 9.3K ohms), and added a pair of cast Alnico magnets. I used Alnico 5 because I had them on hand but these could easily be replaced with Alnico 3 which I am sure it had originally.