This circuit was found in a 1924 Gernsback publication. The variable capacitors are dual. Listening is through a high-impedance phone.
This basic configuration can be found in a lot of articles on this site. In this case, the relay...
This circuit is from American documentation from the 1980s. The transistors are general purpose...
The circuit is simple, as it uses only one transistor and a relay that can be MC2RC1 or MC2RC2,...