Charger protection relay (CB26312E)

This circuit was obtained from an Elektor magazine from the 90s. The circuit is to protect batteries while charging.

RF Switch with Varactor Diodes (CB24707E)
Varactor diodes are our varicaps of today. This circuit for switching signals in an RF circuit was found...
Unit Gain MOSFET Amplifier (CB6128E)
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
Pulse Counter (CB24087E)
This circuit digitally counts input pulses. The circuit from a November 1970 Radio Electronics uses...