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.

Speed Alarm (CB4956E)
This circuit was obtained from an old documentation, but as it uses still current components it can be...
Battery charger with current and voltage limiter (CB9537E)
This battery charger circuit was found in ancient American documentation. The components are...
Delay Circuit with PUT (CB13287E)
This circuit is from a technical documentation from the 70s, and equivalents can be used for...