Crystal set radios
Crystal set radios were a hobby I had in the 1930s. In the back of the Popular Mechanics and Popular Science Magazines, there were ads for parts that you could send for. I sent for these parts and assembled them. The parts consisted of a crystal, earphones and a coil made up of copper wire wound around a cylinder to select the station frequencies. An antenna that helped to increase the reception was made up of a copper wire between two insulators. It always had to have a ground. The way my mind worked, I thought it would be neat to listen to the radio sitting 30' up in our black oak tree in our front yard. I attached an antenna from this tree to another large oak tree in our yard and installed 100' of copper wire on insulators from tree to tree.
There were three strong radio stations in the area that I could pick up. You had to listen to this with earphones because there were no batteries involved. The only source of power was the crystal and the fine-tuning was with a wire that you had to touch to find a sensitive area of the crystal to produce more volume. After using a crystal for a time, it would become weak, and my dad told me to soak the crystal in vinegar to revive it.
I built a crystal set radio with all the parts concealed in a walnut block of wood with a Mickey Mouse cutout attached to the top. I also had a pen and pencil holder on the top of the walnut block with my name engraved on the front. I was really proud of this.
On the Internet, I found that there is still a wide interest in building crystal sets and even belonging to crystal set clubs. I was totally amazed to find the exact earphones that I bought then now cost $110.