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Rubber-Covered Wiring in 1939-1942 Philcos The bane of the later prewar Philcos is the extensive use of rubber insulation on the wiring. Philco even used this wonderful stuff in the power transformer leads of many 1939 models. Fortunately, they soon switched back to cloth in 1940 for their power transformers. Unfortunately for us, they kept using the rubber-insulated wiring throughout the rest of the set in every home model up until domestic radio production ceased in 1942 for the duration of the war. Likewise, many Atwater Kent sets made after 1930/31, most older Majestic (Grigsby-Grunow) sets, and Zenith radios made after 1938 or so make extensive use of wiring with rubber-coated insulation. These sets are NOT for the novice! The rubber insulation breaks down over the decades, causing it to dry out and flake off. Turn the chassis of the typical 1939-1942 Philco upside down and you’ll likely see many bare, or partially bare, wires, with some old rubber insulation residue on the bottom of the cabinet. The insulation that remains is typically very dry and brittle, and will break apart when touched. This is a potentially hazardous condition, as if one of these sets is plugged in and turned on, and certain wires are touching each other, a fire could result! NOTE: An old radio should NEVER be plugged in and turned on until, at the bare minimum, its electrolytic capacitors are replaced and the power transformer checked for signs of overheating. The rotted rubber insulation issue MUST be addressed in order to have a safe and successful restoration. There are two ways to solve this problem: 1. Replace all of the
wires in the set with new wiring. Let us examine option 1 first. 20-gauge solid wire is an excellent substitute for the original wires, and is available in various colours so that the radio will still look original underneath. Stranded wire should be used for wires, which must flex in use, such as the wiring going to pilot lamp sockets. Again, 20 gauge is fine. Each wire should be replaced, ONE AT A TIME, with a new piece of the SAME LENGTH as the original, routed in the SAME MANNER as original. This is important! If you merely cut a piece of wire and stick it in, regardless of length and/or position, the radio may not work properly (if at all) when you are finished! NOTE: It is VERY IMPORTANT that you replace one wire at a time! If you get in too big of a hurry, it will be easy to forget which wire went where, and you may end up with a non-operating radio! Replacing the wires running to pilot lamps is a problem all its own, as the pilot lamp socket has rubber insulation inside which has deteriorated by now. See the page on Rewiring Philco Pilot Lamps for more information. Now let us turn to option 2. This is actually somewhat easier, as you only have to unsolder one end of the old wire, remove the remnants of the old insulation, slip on new heat-shrink tubing, heat the tubing to make it shrink, resolder the wire back in place and move on to the next one. The tubing should be shrunk to fit, as it will make the new insulation easier to bend. Plus, the form-fit of shrunk tubing makes the wire look original (if the proper color is used). And, yes, heat-shrink tubing is also available in various colors and lengths. I have used both options (rewiring and resleeving) in the past and either way works for me. As long as you are careful and pay attention to what you are doing, it will work for you also. Return to the Tech Section Index. © 1997-2006, Ron Ramirez. All
rights reserved. Unauthorized duplication prohibited.
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