With Christmas behind me, I’m making some progress with the radio restoration project. I’ve replaced about 3/4 of the 73 year old components, but still have about 6 hours of wiring work left to do. Out of curiosity, I’ve tested each original component that I’ve removed to see how close to spec it is. Roughly half of the capacitors were no longer in spec, and most resistors were well out of the 20% tolerance margin. A few resistors had infinite resistance, so this radio would not have worked had I simply replaced the tubes.
I’ve also encountered parts that do not appear on the manufacturer’s schematic diagram. Judging from the solder joints, it’s clear that the radio was modified earlier. Considering the age of the extra parts, it was probably modified in the late 1940s or 1950s. Most of the non-original electronics are electrolytic capacitors, and based on where they were placed in the circuitry, I’m assuming that they were added to eliminate the “hum” that aging capacitors can cause with old radios, but that’s just a guess.
I wasn’t expecting a surprise from the vintage power cord, but as I removed some cloth insulation, it was clear that this cord was covered with felted asbestos. This was common in the old days for power cords that were used for devices that made a lot of heat or used a lot of power, such as irons. I disposed of any loose asbestos and cleaned the wiring.
Still have a lot of work ahead, but it’s fun and certainly an ongoing education.