This circuit was found in a 1924 Gernsback publication. The variable capacitors are dual. Listening is through a high-impedance phone.
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...