This circuit was found in Motorola's 1968 documentation. It can be built on current equivalent components. The bridge diodes and the SCR must be in accordance with the current of the controlled motor.
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....