This circuit can be adjusted between 0.2 and 2 V to trigger with chosen voltages comparing them with the input voltages. We found it in a 1967 documentation.
We found this circuit in a 1968 Electronics World. The transistors are from the era and...
There are several manufacturers of the integrated circuit used and it also admits equivalents. The circuit...
This circuit is from 1971 American documentation. Transistors are still common except for 2N2060...