This FM advertising suppressor (SCA) decoder circuit was suggested by Signetics in a 1980s documentation. The circuitry decodes the 67 kHz signal. The integrated circuit used is of the time.
In the figure we have an application for NLAS5113, a new device from on Semiconductor...
This circuit found in a 1965 Electronic Design multiplies the frequency of a 400 Hz signal...
The output voltage depends on the zener diode. Zener in the range between 1.2 to 12 V rated to 1 W...