One of My inventions that never got off the ground
When I was a kid there were several books written for boys that instructed us how to build all sorts of things from materials that are available everywhere. One example was a Kajak made from plywood. Another was a small radio receiver that could be built into a soap box, or even into a match box.
It had a very simple circuit:
I started building one since I wanted to listen to music when skiing, but it never worked well, it had poor reception and the volume was very limited. There were also no suitable headsets at the time.
Only a few years later Sony then came up with exactly what I had in mind: