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~ 1948 Supro Lap Steel Refurbishment ~ Page 8; Installing Electronics Assembly: |
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The phone plugs of both electronics assemblies must be removed so that their cord can be pulled back through the body's cavity hole. Better to remove the plug than desolder the leads from the pots. The donor plug is modern and not worthy of archiving. But the old original plug is an entirely different matter: The original plug is the REAL DEAL; The grand-daddy of all plugs; WWII military surplus ....or telephone company surplus, designed to be pushed in and out of jacks by telephone operators hundreds of times each day; ( "Number please" ....503J ...."Connecting to 503J" ! ! ! ). "Bullet proof"; Solid brass; Manufactured to Navy specs, ....the old equivelant to today's Mil Specs. They were still the identical plugs when I worked in a Army electronics research lab in 1967; I even remember that the numenclature number started with 'PN' (Plug, Navy) followed by a dash and configuration number, printed on the screw-on casing in thin white lettering. 63 years old and still as good as new ! Documenting how to solder cables to these plugs is good info for any plug. |
To remove these plugs; Unscrew the tip lead and desolder the remaining connection(s) and pull the plug off of the cord / cable. Heat remaining solder on the plug and immediately tap the back end of the plug onto a hard surface to make the hot liquid solder jump off; Aluminum foil will protect a surface from the hot solder. Then use a snap-suction desoldering tool and a wet rag to remove any remaining solder heated hot to liquid, ...but leaving appropriate previously soldered points tinned. After removing small or valuable parts from a guitar, bag them up so they won't get separated or otherwise lost; Especially when small parts of an assembly are involved. |
Before beginning to remove a plug, pull the screw-on cap up the cord and tie a loose knot so the cap sleeve won't slide back down on the remaining work; And few things are as agrivating as laying a cap sleeve on the work bench then forgetting to put it on before soldering a plug on .....and having to R&R the plug again to get the cap sleeve on ! |
I save the end of the old cord if it fit well. It will provide a measuring pattern to strip the cord for resoldering onto it's plug. |
Strip the outer cloth insulator back. Unweave the braided ground shield by stroking it towards it's end with the tip of a round toothpick. Pull too hard with a toothpick and the toothpick will break; Pull too hard with some other strong tool and the wire will break. Strip the middle nylon cloth insulator back............ |
Strip the inner nylon cloth insulator back. Twist the ground shield and tip wires ready for soldering. Pay good attention to getting all of the single wires in the tip wire twisted tightly together with no single wires sticking out; The tip wire will have to be small enough to go back into he small hole of the donut connector, yet retain it's single wires for good conductivity and least resistance. |
Spray the wires with contact cleaner and brush them clean with a small wire brush. Lightly flux the ground shied and tip wires; Then tin (prime with solder) the tip wire but not the ground shield wire. The ground shield wire will tin itself later in the process. |
Pull the center nylon insulation cloths back and clip on a heat sink to the center / tip wire. The tip's donut connector should have been desoldered with a solder-sucker and cleanup up when it was removed. It should have enough solder left on it to be tinned, and should slide right onto the tinned tip wire. All held in place in the soldering jig. |
Solder the donut connector to the tip wire. Desolder any access nice and smoothly; Applying the solder gun to the bottom of the work will make excess solder gravity feed back onto the soldering gun tip. When the joint has cooled, remove the aligator clip heat sink. |
Tin the end of the anti-stress coil generously if it isn't already tinned from removal; It was in this case. Apply some flux to the coil's tinning when it's cooled; That will flash the solder down through the coil and into the twisted and fluxed ground shield wire when it's time to do that soldering but not yet. Bend the ground shield back flat against the cord and install the anti-stress coil over the ground shield and cord. Notice that the coil will loosen on the cord if turned in one direction, making installing it much easier, but will tighten if rotated in the other direction and thus prevent installation. Scrub off the flux residue from the donut connector. File down any bumps or snags on that connector. |
Some interesting and potentially useful trivia: The most efficient way to solder cords into these plugs for musicians and the general public, is not the way they were designed to be soldered in; But the soldering and attachment should be made even more bullet proof for musicians and the general public than for well trained military and telephone company employees who properly put all of the pulling tension on the plug casing and not on the cord / cable and spring coil. Here's how these plugs were designed for cord attachment: The cord's different layers were stripped to fit, like shown later on this page. The ground wire was soldered to a donut connector like the tip wire is on this steel's plug; So that soldering and de-soldering would not have to be done in the high maintenance of telephone plugs and field maintenance of the military. The cord had a very durable outer insulator; Durable cloth at first but changed to rubber impregnated with nylon strigs during WWII for the military and the 1950's for civilian use. A spring coil the same size as this guitar's was rotated onto the end of a wider cord, as this narrower cord and plug does (shown later); Turning the spring coil in one certain direction would make it looser on the cord and "thread" itself up the cord end ....and the spring coil would tighten back up and thus clamped onto the cord tightly when the turning tension was released. The outer diameter of the spring coil would fit tightly into an interior seat machined into the plug. A cuff slot was machined into the plug's outer casing, which was used to wrap a strong sturdy string tightly around the spring coil and in the cuff slot, and then hand tied. The string dug into the spring coil's texture and held the coil and cord tight and strong. |
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See below for arrows meaning. |
