This 80's Exar circuit has a carrier detector for frequencies up to 500 kHz. The circuit uses a company 567 which is still a common component.
This comparator with two Texas Instruments operators was obtained in a company application manual....
This blocking oscillator that appears elsewhere on this site from other sources, was found in a...
In this circuit R1 is 56 ohm and R2 is 220 ohm for the 110 V network. SCRs are according to the...