This circuit uses a 555 (according to the diagram) to generate 50 ms tone bursts at a frequency of 1.5 kHz. The circuit is from an 80's Electronic Design.
This traditional clock circuit with common CMOS components with discrete logic functions was found...
Although ECL logic is rare (no longer used), this circuit from a 1992 documentation shows how to...
Found in 1965s General Electric documentation, this circuit is intended for the control of servos...