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.
This alarm, found in a 2002 documentation, uses several sensors and has a 12 V supply, not...
This circuit uses a special 1950's RCA strobe tube. It can be built with equivalent components for the rest...
This circuit, which can act as a shield, was found in a 1970s American documentation. The...