Digital recorder ISD1016 (CB7963E)

Found in a Popular Electronics from the 90s, this digital recording circuit uses an unusual integrated circuit today.

Darlington Touch Switch (CB7191E)
This circuit is from 1968 General Electric documentation. It can certainly be adapted for any...
Capacitor Tester (CB4391E)
This tester from a 1960 magazine is only for capacitors with insulation voltages above 200 V (110...
Unijunction Telegraphy Oscillator (CB12283E)
Found in a 1991 publication this circuit can be assembled with more modern components. We can use...