rated at 2250 ohms Z for picking up spring vibrations and feeding them to an opamp input, or could be used or tube grid, this came out of a Fender Hot Rod DeLuxe.
you can make this transducer more bulletproof by using #42 AWG .003" wire.
it will fit with room to spare. wind the first layers with light tension and it will never break.
use good wire.
you can unhook the springs from the magnets, there is a little wax in there to keep things from rattling, but the spring will come out. this saves the touchy and difficult task of un-soldering the magnet wires where they connect at the back of the two brass fittings, as getting the wires back through the insulating material in the fittings is a chore.