Digital recorder ISD1016 (CB7963E)

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

Signal Rectifier (CB13652E)
This precision signal rectifier was obtained in an American technical documentation from 1975. The...
Permanent magnet detector (CB22463E)
We found this circuit in Popular Electronics from 1992. Transistors admit equivalents....
Triac Switch (CB25067E)
This control circuit using a low voltage switch was found in the September 1987 Radio Electronics...