This circuit was found in the October 1989 issue of Radio Electronics magazine. It drives an auxiliary relay with the call signal for a possible louder bell.
This circuit is based entirely on SCRs. The circuit is from an American 80's documentation; and the PUTs...
This circuit is used in transceivers, enabling input selection by diode switching through polarity...
This 80's circuit uses a small light bulb as an indicator, but an LED with the appropriate resistor...