This crystal or galena radio uses a germanium diode. C1 is an old radio variable and L1 has 100 turns of 26 or 28 wire in a 1 inch PVC pipe. The antenna must be a long wire.
Found in documentation from the 1980s, this circuit can generate signals in a range that reaches a few...
Found in a 1967 publication by General Electric, this control is intended for motors up to 2 A...
This circuit was found in a 90s Popular Electronics. The circuit uses components from that time,...