In use telephone indicator (CB8657E)

Found in a 90s Popular Electronics, this circuit keeps an LED on when a phone is in use. Can be used with extensions.

Up to 60 V x 5 A power supply using the 741 II (CB1218E)
This circuit was obtained in an 1975 English publication. It is a voltage regulator circuit for...
Infrared receiver (CB7822E)
In the figure we have an infrared receiver circuit using an operational 741. The circuit is an...
Negative Voltage Regulator (CB15903E)
This circuit is suggested by National Semiconductor and makes use of the negative regulator LM2990...