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.
This circuit was found in an Electronic Design from 1967. The circuit uses two triacs being T2...
Found in old American documentation, this circuit can use crystals between 27.5 and 33 MHz...
This shield from the 60's uses a germanium transistor of the time and a common type of relay of...