This crystal or galena radio was found in documentation from the 1990s. The earpiece must be a high impedance crystal or magnetic earpiece and D1 can be any germanium diode.
We found this circuit in an old documentation from the 70s. The sensor is an LDR that must be...
This circuit with junction field effect transistors was found in documentation from the 1980s. The...
Common general purpose silicon diodes when direct biased provide a voltage fall of about 0.6 to...