Found in Popular Electronics from the 90s, this circuit uses a reed switch on the rails as a sensor. Instead of lamps, in a modern version, LEDs can be used.
This circuit was obtained in a 1960 transistor manual from Sylvania. The circuit uses small...
This 1980s documentation circuit uses a 741 in a different high-speed comparator configuration. The feed...
This is the typical circuit of a 60's tape recorder. The circuit uses only two transistors and has a...