Metal detector receiver (CB22457E)

Found at Popular Electronics this receiver is used with a transmitter for quadrature-coil signals.

FM or VHF Receiver (CB4578E)
This 1995 circuit uses an audio amplifier that is no longer common today. However, other...
Window Generator (CB9460E)
Found in a Popular Electronics from the 90s, this circuit uses common components with several...
Audio Operated Relay (CB5985E)
This circuit is from the 80's but uses common components today. The relay is voltage sensitive...