MAKING SHIELDED WIRE WITH A WOVEN COTTON INNER

Old style screened cotton covered wire can be easily made.

I was restoring a Kingsley AR7 receiver from 1940 and I needed some wire to replace the non authentic plastic wire I had removed. Some of the later manufactured AR7 receivers of the 1950s were wired with plastic wire, but I am refering to the earlier ones here. To keep the components in the same period, I was using woven cotton covered multi-strand wire to rewire it, obtained from my junk box. I needed some screened wire for the leads to the volume control, the BFO, and for the valve top cap connections. All the pieces of screened wire I had, were either too short or too modern, so I decided to make some screened cotton wire. It is easy to do.

You need some woven cotton covered multi-strand wire for the inner, and any normal wire of the period will be suitable. You also need some braided or woven wire for the outer. To make this, find some modern quarter inch diameter coaxial cable. Cut a length of about 12 inches long, as if it is too long, it is difficult to strip. Grab the inner with a pair of pliers, or clamp the inner in a vice. Pull the outer with your hands, and it will come off, leaving the inner behind. You now have in your hands, the plastic outer tube, with the woven braid inside it. Grab the braid with some pliers and it will pull out. Be careful not to squash the tubular braid. Solder a draw wire to the cotton covered wire and thread the draw wire through the woven braid. Slip the braid over the cotton covered wire. Smooth it out so that it is a tight fit. Cut it to length. You now have shielded cotton covered wire. When you choose the coax to use, ensure that the braid inside it, is made of tinned wire, so that it looks correct.

You can use the discarded inner wire from the coax, with the clear plastic dielectric, as high voltage insulated wire, if you need some for repairs of more modern equipment. The plastic outer can be used as large diameter spaghetti, also on more modern repairs. Any left over braid can be flattened and used as flexible earth strap. The tuning capacitor in the AR7 is connected to the chassis and the metal shields with this type of braid, so it can be used to repair or replace any broken and missing braid. The normal AR7 uses tinned braid, but the Army version of the AR7 (called the "Reception Set Number 1" or also known as "Communications Receiver Aust. No. 1") uses unplated or natural copper braid. Choose a different type of coaxial cable, to make this braid.

The photograph shows the disassembled coaxial cable, with the empty plastic tube (at the bottom), the clear plastic dielectric containing the inner wire (second from the bottom), and the empty tinned woven braid (third from the bottom). Next is the woven cotton covered wire (fourth from the bottom), and finally the finished shielded cotton covered wire (at the top). The small piece at the top right is a flattened piece of braid, suitable for an earth strap.