This elaborate mixer is from an Electronics Today International from the 80s. Operational amplifiers are common and resistors with no value determine the gain of the amplification steps.
This circuit was obtained in a 1967’s EEE. Transistors and integrated circuits can be replaced by...
This source, found in a 1991 publication, was originally designed to operate with the CB18736E, an alarm...
This circuit is from Motorola's 1990 Linear Databook. We can implement it with other operational...