The integrated circuit used in this circuit from a 1987 documentation is no longer common today. This circuit can generate a multitude of different sounds and this circuit is an example of application.
The transistors are 2N918, 2N3464 and other RF equivalents of the time for Q1. For Q2, 2N3399, 2N2894...
This circuit, which can be used as a shield, was found in a 90s Electronic Design. The circuit...
This interesting intercom circuit was obtained from an Argentine publication from the 1970s....