This circuit is from General Electric documentation from 1970. The transistors can be of general-purpose types, except for the power that can be a BD136.
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...