This circuit is from a technical documentation on the National Semiconductor LM3909. The tripping transformer has a 1:1 turn ratio and the circuit is powered with 5V.
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...