Found in Ferranti's 1969 documentation, this circuit can be mounted with a modern equivalent transistor. The circuit has a 4 V immunity and can be used as a shield for sensors.
Found in a 1980’s documentation, this circuit must have its signal applied to an amplifier stage. The...
This SCR circuit, which can also be used for signaling places, was found in old American...
Found in a 90’s HAM Radio, this circuit is used for an optical communications system or even audio...