While repairing an old Ham radio transmitter back in high school, I found a bad capacitor. It was a large metal-can electrolytic type, bolted to the steel chassis of the radio. Because it was part of the negative 250 Vdc bias supply, the can was isolated from the chassis with an insulating fiber washer. Unfortunately, the replacement capacitor didn’t come with such a washer, and I couldn’t use the old one because it didn’t fit. Not to be deterred, I decided to make my own custom insulator using a piece of rubber cut from an old bicycle inner tube. To this day, I still remember the small explosion that resulted when I flipped on the power switch, not to mention the odor that was released – I dubbed it “Essence of Midnight in Pittsburgh”. I learned the hard way that inner tubes are not just rubber, but contain a substantial amount of carbon black and therefore don’t make very good insulators.
