Found on a 1964 CQ this circuit is intended for tone frequency change modulation (FSK) telegraphic transmissions. It operates with signals of 2.975 and 2.125 Hz.
We have dozens of similar projects in articles and circuits on this site. This is from Radio...
This circuit with an unusual configuration was found in the January 1974 issue of Radio...
This interesting circuit from 1967 documentation uses three series lamps to regulate the voltage...