We found this circuit in a 1957 Raytheon transistor publication. The circuit can be assembled with more modern transistors with minor changes. The handset must be high impedance magnetic.
This TTL circuit for digital signals up to a few dozen megahertz was found in old documentation, but...
This circuit with an operational amplifier was found in the magazine Radio Electronics of...
This detector is from the 1990 Motorola Dataar Databook, but can be adapted to work with more...