Found in a 1924 book by Gernsback, this circuit uses a double variable capacitor, a component not very common at the time. Listening was done on a loudspeaker at the time.
We found this circuit in an old Mullard (Philips) documentation. The sensor consists of a...
This simple circuit, powered by 4 batteries or 9 V battery, brings together several functions of...
This circuit was found in an American documentation from 1977. The mechanical resonator or ceramic...