Battery voltage monitor (CB7133E)

We found this circuit in a Popular Electronics from the 90's. The circuit activates an oscillator when the voltage exceeds the value set in R5.

Selection of diode inputs (CB4111E)
This circuit is used in transceivers, enabling input selection by diode switching through polarity...
Unit Gain MOSFET Amplifier (CB6128E)
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
Distortion Free Pulse Delay (CB6661E)
This circuit of 1965 documentation makes use of a tunnel diode to retard a pulse without...