Found in an American documentation from the 90s, this circuit has a configuration that has been extensively explored in other articles on this site. The FET can be the MPF102 or equivalent.
This filter for the 300 Hz to 3 kHz range was found in an American documentation from the 90's....
The battery is charged by the photocell that keeps the low consumption beacon in the dark. The...
This is the typical circuit of an FET amplifier stage in the common source configuration. The circuit is...