Restoring the old

So I'm in my shop, minding my own business, and in comes this minty 1965 Guild Capri. Played beautiful, but had a strangely weak neck pickup. The fellow that came with the guitar had been through ever conceivable wiring repair to the circuit: jacks, pots, capacitors, lead-wires, all to no avail. Still a tinny whisper that all but died when the tone was rolled down. Well that makes sense, I thought, it seems that is all the pickup is giving-treble. But why?

The likely culprit here was a broken coil wire in the pickup. Some current was being generated with each strum in the remaining coil, but not the full amount you get with a continuous loop of wire. Heaving the heavy sigh one heaves, I set to remove the neck pickup volume control from the guitar for pickup testing. Just in the nick of time a past experience with a mid 60's Gretsch Rock-Jet reminded me of the following tip: lots of times in these old midrange hollowbodies there were plugs and terminals on the pickup end of the equation for easy assembly. Sure enough, when I gently removed the pickup and plate, there were two solder terminals, just waiting to be tested. They read open circuit, indicating that the precious internal coil wire had been severed. I subsequently removed the bridge pickup and it read in 6.7kohms of resistance around the coil. We'll save that measurement for later. 

An electric guitar pickup is just a coil of thin coated wire, near a magnet, connected at either end to a guitar cable. This coil wire is the diameter of one of my little bald guy hairs, and there are literally thousands of continuous winds. To keep all this organized, you need a bobbin onto which the coil can be wound. Some bobbins are easy to get to. Others, like these are covered in a chrome shroud. Here you can see the bottom plate of the pickup on the left, and the underside of the bobbin and shroud to the right. Once I get in there, I may be able to find the snapped wire and bridge it back together. If not, the coil will be cut off and the pickup rewound.

Under the shroud I found an unfortunate surprise: both bobbins were cast in plastic after winding to keep everything from wiggling around and generating feedback. On top of this I found twenty broken connections from a time in the past when someone tried to remove the shroud with what I imagine was a butter knife or the like. They busted clear through the bobbin and just obliterated the coil wire. Much too much to patch. This pickup will be rewound. The fused bobbins will be sawn down the middle and their individual coils exposed...

...and cut off with a special razor...

...until the bobbins are clean and ready for rewinding.

My coil winder is a simple machine. The bobbin mounts to a flat plate which spins eight revolutions for every one crank of my wrist. An old caliper is used to align the coil between extremes so it doesn't come off the bobbin as it is winding. An odometer style counter keeps track of my winds. Lets see, our bridge pickup tested at 6.7kohms of coil resistance, and it's nice for the neck pickup to be just a shade weaker than the bridge to make up for the wider vibrations at the neck position...so let's say our target will be 6.5kohms for the neck pickup. The pickup has two coils though, so each must be wound to 3.25kohms. As I wind, I stop and check and eventually do a little math to determine how many winds will be equivalent to the target resistance: 3.25 kohms per coil. 

Here you can see both coils fully wound and back together. The output is tested, and reads just where it should, so shroud can be soldered back on and the pickup installed!