In the figure we have a stereo decoder from the 70's with pilot lamp for signal indication. The circuit employs a component of the time, which is uncommon today.
This configuration for latching automation using relays was found in Radio Electronics magazine from...
This circuit was found in Motorola documentation from the 1980s. PUTs are not common components...
This circuit is based on a regulator component that consists of a transistor and zener in the same...