This elementary receiver with a crystal earphone was found in Japanese documentation from the 1960s. The coil has 60 + 40 turns of wire 28 to 32 in a ferrite rod.
The circuit shown in the figure is a simple test of NPN and PNP transistors. The circuit detects the...
This circuit is from an old American documentation, from 1977, but it can be implemented with more...
Found in a manufacturer documentation from the 90s, this circuit makes use of period components. The...