The RCA integrated circuit used in this control is uncommon today. The circuit is from an Electronics Now from July 1995. The sensor determines the value of the adjustment potentiometer.
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....