This circuit for the 60 kHz range was found in 73 magazine and published in 1995. The circuit uses a ferrite rod. Note the direction of the coil windings.
An advanced motor control software plug-in for Microchip’s MPLAB® X Integrated Development...
This relay without lock uses a general-purpose transistor. The relay is according to the supply....
This signal follower is from a 1970's documentation. So it uses the traditional configuration at the time...