Years ago I pulled apart a Fender Telecaster pickup and saw string wrapped around the coil to protect the magnet wire that saturated with black wax to help reduce moisture from penetrating the pickup and used to eliminate microphonic feedback or squeal. The theory came from the transformer industry to coat the coil and keep the coil windings firmly in place.

The Fender company wax potted the early coils in wax as the bobbins were made from a paper product such as vulcanized fibre and even old time cards were used. The paper pieces were cut, punched and fabricated into bobbins for supporting the windings of the coil. After the bobbins were wound the coils were wax potted to keep the coil firmly in place. The early pickups had lamp black or black carbon added to the wax to make it more opaque and less visible inside the mounting or bridge plates. The lamp black dyed the string around the early Broadcaster, Esquire and Telecaster pickups also using the blackened wax the assembler could tell that the pickup was finished and ready to be used in assembly.

I’ve seen many single coil pickups where the wax didn’t fully saturate or permeate the coil. If a wire vibrates or a metal cover is loose an oscillation or eddy current can produce uncontrollable microphonics or feedback. Proper potting saturates the coil with hot wax and fills all the gaps inside the pickup to eliminate the parts from vibrating. Potting pickups is easy as dunking a candy apple but it’s dangerous and “you must be careful.”

MATERIALS NEEDED:

Candle, canning or special industrial wax- found in most hobby shops or craft stores.
Double boiler- water in the bottom container and wax solution in upper container.
Heating element- electric stove or portable heating element. Do not use a gas stove or open flame! I use industrial wax melting pots. They are expensive too.
Paper towels- for blotting and wiping excess wax off pickups.
Wax paper or cardboard- to place pickups after they have been wax potted.
A cooking thermometer that measures between 130-180? degrees Fahrenheit (F).
Eyeglasses- to protect the eyes if you splatter hot wax.
I use gloves to keep the hot wax of my hands and fingers.
Support wires- I make wire hooks to help hold pickups so they can be agitated.
. Cooling fan- This helps cool the pickups faster as hot pickups can loose most of the wax if allowed to cool too long.
PROCEDURE:

Buy paraffin candle wax at a hobby shop or where canning supplies are sold. Use a natural color wax when potting gray fibre pickups. Stay away from bee’s wax as it is too soft and sticky.
Heat the wax in a double boiler. A set of two nesting saucepans in which the contents of the upper are heated by the simmering water in the lower. Melt the wax slowly and keep the water below from coming to a boil.
Use your thermometer and when the wax melts around 160? degrees Fahrenheit, keep it at that temperature and no higher!
Read the “RECIPE” section below for desired pickup potting. This gives recommendation on how long to immerse various pickups.
Hold the pickup or attach wires and gently lower it into the wax. Alternately draw the pickup back and forth and bounce it gently of the bottom of the container. This gentle tapping loosens built up wax and eliminates air pockets inside the pickup.
After desired potting remove the pickup from the how wax, let drip till the wax slows down and put the pickup on wax paper or cardboard. I move the pickup often when cooling so the pickup doesn’t stick to the paper.
NOTE:

When measuring the DC resistance of hot pickups the resistance will be much higher than at room temperature. I often cool pickups using a gentle fan about a foot away from the pickups. I also used an industrial vacuum system to help remove air bubbles from voids in the pickup when wax potting. Agitating will help do the same thing but will take longer.

Gently blot the top of the pickup with a paper towel to remove excess wax that could make it difficult to firmly seat a plastic cover. Do not squeeze the coil as it can force out the wax and distorting the shape of the coil. Using a paper towel or tissue, gently wipe off excess wax on metal covers. Keep the metal covered pickups bottom up.
Avoid handling the pickup till it’s cooled down after about an half hour. This allows the wax to set and holds the components of the pickup firmly in place. Also keeps from getting fingerprints all over the pickup.
RECIPES:
Proper potting depends on complete permeation of the pickup in wax.

Telecaster Lead with metal bottom plate: Loose bottom plates on early Broadcasters, Esquires and Telecasters is one of the main causes of microphonic feedback using higher amplification. I keep screws in the three elevator height adjust holes to keep the bottom plate secure to the bottom of the bobbin.

I submerge the pickup in hot wax not exceeding 160? degrees Fahrenheit.
I agitate the pickup for approximately 1-3 minutes.
When the pickup is first submerged the wax cools and coats the pickup.
Agitate the pickup to loosen hardened wax and loosen air bubbles.
When the air bubbles stop and completely saturated remove the pickup.
Place the pickup on the wax paper or cardboard-occasionally move to keep from sticking on the paper.
Blot the top and bottom of the pickup to remove any excess lumps of wax
I keep the top of the pickup facing down. This puts a thicker coating of wax on the upper edge of the pickup and helps protect the coil if accidentally snagged.
Cool the pickup fairly quickly to stop the hot wax from dripping out.
Telecaster Rhythm: I always keep the metal pickup cover on when potting the rhythm pickup. These pickups have always been known to howl even at lower volumes. I also keep the bottom up on these pickups too. The metal cover can retain much heat that can melt the wax back out of the pickup if it was top side up. The wax would just drip out. Follow the same procedures from 1 to 9 listed above.
Stratocasters, Duo Sonics, Jazz Bass, Precision Bass and including all other Fender Single coils.

Extreme care needs to be taken as the coils are exposed on these model pickups. The covers should be removed (all plastic covers) as they can melt or distort in the hot wax. Be careful when agitating the pickups that you don’t hit the coil and damage the windings. Breaking one turn of magnet wire will cause the pickup to fail. Agitate slowly and carefully and avoid banging the pickup too hard on the walls of the container. Follow the procedures for the Telecaster lead from 1 to 9 listed above.

PICKUPS WITH PLASTIC BOBBINS: EXTREME CARE MUST BE DONE!

Humbucking Pickups,

Soapbar or Dog ear P-90s,

Mini Humbuckers, Firebird pickups.

Most manufactures use various types of plastics for injection molding bobbins or coil forms on many styles of pickups. The materials used for molding have varied molding temperatures that can distort when exposed to hot wax. It is extremely important that you carefully watch the pickup at all times. The bobbins are under extreme pressure when the coil is wound and subjected to high temperatures. There can be extreme stress and tension on the coil form that can shrink distort when subjected to heat. Certain components used in making humbucking style pickup’s can retain a high amount of heat such as magnets, studs, pole pieces, covers and bottom plates.

When the pickup is first submerged the outer surface can frost over with cooled wax.
Agitate the pickup to remove the film of thick wax till the components warm to the temperature of the wax.
Soon after the bubbles diminish get ready to remove the pickup.
The potting time can vary and extreme caution needs to be taken to watch the pickup.
Don’t leave the pickup unattended as it can start shrinking and distorting the poles.
Each pickup needs individual attention and devoted time when wax potting
If the pickup had a metal cover, place the pickup bottom up.
Quickly cool the pickup to eliminate excess wax from exiting the components.
Note: I always agitate the pickup and quickly get it out of the hot wax. This will reduce possible damage to the coils and inside components.
Wipe excess wax off the outer cover and blot the bottom plate while cooling.
After the wax thickens and is a non drip state, the pickup can be picked up by the legs and turned over and the top side of the cover can be wiped clean of excess wax.
On adjustable pole pieces, I raise the poles and clean out with an old tooth brush to remove the wax within the slots and screw back in to desired height and allow to firmly cool.
When potting pickups with no covers and the coils are protected with a special tape: Carefully pot and firmly press back into place the loosened tape. I’ve often put rubber bands around the coil to keep the tape from unwrapping due to the hot wax. After the wax cools, the tape normally stays in place. You need to agitate the pickups slowly to reduce peeling of the tape.
POTTING EPOXIED PICKUPS:
Wax potting epoxied pickups can rather difficult because the thick epoxy covers the components but is usually to thick to permeate the coil and fine voids. Air pockets can still cause microphonic feedback in epoxied coils and I try to avoid this type of potting especially on passive or non active pickups. Wax potting might help if it can seep into voids left unfilled by the epoxy. Epoxied pickups are difficult to repair or rewind when broken. Earlier epoxy resins would shrink and often caused the pickup to eventually stop working.