This circuit was found in Radio Electronics from the 90s. The CMOS integrated circuit is a PLL not easy to obtain today. The output stage can be exchanged for another one with greater power.
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....