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.
The presented circuit emits signals in the FM band, which can be picked up from a distance of a...
I found this circuit in a documentation for radio amateurs from 1975. The FET could be the BF245....
The traditional inverter amplifier configuration with the operational 741 shown in the figure is...