The circuit shown is from National Semiconductor's Linear Applications Handbook. It makes use of the LM78S40 which is not an easy component to obtain today.
In fact, this is the circuit also known as “vox”, that is, a relay triggered by sound. This...
Based on an LM36000 OTA this circuit was found in the July 1988 issue of Radio Electronics...
Relays up to 100 mA can be driven by the 555 with the recommended circuit. The circuit is from an...