We found this circuit in an American documentation from 1947. The circuit uses 5 tubes and has a feature to keep the tube filaments preheated.
In this circuit the relay triggers on when light falls onto the sensor, a common LDR. Power supply...
This circuit emits a warning sound when night falls. The circuit is from a Hands On Electronics from...
This circuit can measure capacitances in various ranges using a common analog indicator. The...