Voltage Level Detector (CB22135E)

We found this circuit in an English documentation from the 80's. Transistors are general-purpose types.

Undervoltage protection (CB8028E)
Found in 1967 Raytheon documentation, this circuit uses a company coupler consisting of a lamp and...
Universal Crystal Test (CB21786E)
In a modern version this circuit can use an LED in series with a resistor in place of the lamp. The...
Simple Locked Alarm (CB18097E)
This circuit, when triggered, locks, and remains so until the source is switched off for a moment or...