This circuit is from a documentation from the 70s. The circuit uses logic gates of the time, which in many cases were arrays of transistors allowing use as audio amplifiers, as in this case.
This high-performance circuit was found in the 1982 SGS Linear Integrated Circuits Manual. The...
Found in a 90s Electronics Engineering, this circuit makes use of components of the time. The...
Found in a magazine 73 for radio amateurs, this circuit has two settings, one for the interval and the...