In use telephone indicator (CB8665E)

This circuit was found in a 90s Electronics Now. The circuit can use a TIC106 for the SCR.

Controlling a blinking LED with LDR (CB24662E)
The figure shows how to control the blinking of a 5 V blinking LED with an LDR. The LED only...
Band pass amplifier (CB7447E)
Suggested by Maxim in documentation from the 90s, this circuit has its response curve given next to...
Temperature Alarm (CB6111E)
This circuit is from a 1965 General Electric publication. It uses a thermistor to fire a reed...