This circuit operates at a voltage of 1.3 V from a single mercury cell. We found in an old documentation and for the components used the frequency is 500 kHz.
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....