This circuit is from a Hands-On Electronics from the 90s. The integrated amplifiers used are well known. The range is a few tens of meters depending on the resistance of the cables.
This receiver was found in the Radio Electronics magazine of March 1953. It tunes to the medium wave...
The LED is optically coupled to the LDR1 sensor to provide negative feedback to the circuit and...
The circuit presented was found in a 1988 documentation. It consists of an alarm siren that it...