Using 4 tubes, this 1924 receiver combines new technologies as an intermediate frequency stage that was already beginning to appear. Listening is via phone and battery power.
In the original publication of the 90s a 556 consisting of a double 555 is suggested. The circuit...
This circuit was found in a 1966 EEE. The circuit uses transistors from the time but can be made...
This circuit can be used in alarms by activating a relay or a current load that depends on the...