This circuit was found in an English publication from 1967. The circuit is for listening on a phone. Transistors are types of germanium of the time.
This circuit has been found in an old American documentation and is intended for calibration of radio...
Many reed switches can be wired in series to perform na efficient alarm as shoen in the figure....
This voltage regulator from STMicroelectronics provides a 1,2 A current in the voltage range from...