This circuit is from a Radio Electronics from April 1964. The circuit uses power transistors of the time, which must be mounted on a good heat radiator. Modern equivalents can be used.
This Salen-Key filter can use any operational amplifier and other frequencies can be obtained by...
This circuit can be adapted to be used in a follow the line robot. It was found in the May 1962...
The circuit in the figure uses two of the 4001's four gates to trigger a relay in a timed manner. The...