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 circuit, from ancient French documentation, produces a rectangular pulse from input pulses...
This control is from the Motorola Circuit Applications for the Triac of 1971. The Triacs can be...
This circuit is from 1964 documentation but can be easily implemented based on current components....