Solid state relay (CB8518E)

This circuit was found in a 90s Popular Electronics. Both the coupler and the MOSFET can be of any type.

LM390 Intercom (CB25310E)
This two-channel wired intercom was found in the April 1990 issue of Radio Electronics magazine....
Magnetic proximity sensor (CB7920E)
This sensor triggers an oscillator emitting sound when a magnet is approached by a reed switch....
1.3 V Regulator (CB25901E)
This circuit is based on the voltage drop of the diodes in conduction, in the order of 1.6 to 1.7...