This circuit is from a Radio Electronics magazine from July 1979. It uses the well-known IC 7107, a liquid crystal exciter that became popular in circuits of this type at the time.
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....