This circuit was found in Ferranti's 1967 documentation. The circuit drives a 40 V relay, but it can be adapted to operate with sensitive lower voltage relays.
This audio oscillator is from a 1957 Raytheon publication. The tone generated depends on C2 and C2...
This oscillator, which can be used as a signal injector, was found in a Popular Electronics from the 90s....
Found in Popular Electronics from the 1980s, this circuit is intended for switching filters with...