This circuit from July 1975 Radio Electronics uses any operating system with a symmetrical source. The waveform is shown on the side of the diagram.
For those who like experimental circuits, here is a sequential flasher system with LEDs, which can be...
This circuit was found in an ancient American documentation. The integrated circuit is of the time...
This circuit was found in a 1977 Radio Shack documentation. The circuit is tuned to 1.4 kHz, but...