We found this circuit in Ferranti's 1974 transistor manual. The components are from the period. The table gives the value of C1 for different frequency ranges.
The resistor Re determines the current in the LED and can be changed. The circuit is from a 1978...
Motors up to 2 A DC can be controlled by this circuit that we find in the manual for linear...
This type of logic is no longer used today. The circuit is from an old American publication and...