This circuit recognizes a tone determined by the tuned input circuit (R3 / R4 / C2). The circuit was found in Radio Electronics from the 90s. The 4046 is not a common component today.
Found in a magazine 73 for radio amateurs, this circuit has two settings, one for the interval and the...
This good quality amplifier found in a 1982 documentation has a traditional complementary output...
A low frequency divider can be made using common unijunction transistors as shown by the figure...