Using the CA3140 in the figure we have a comparator that goes low in the window voltage space. The circuit was found in June 1986 Radio Electronics magazine.
This amplifier with complementary symmetry output and good sound quality was found in...
This circuit should be placed between the signal source and the input of a recorder or amplifier....
Found in an Electronics World of 1968 this circuit can use current SCRs and the diodes are...