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.
Found in an American documentation from the 1960s, this circuit uses transistors from the time. The...
In the figure we have a typical configuration with operational, which can be different from the...
This limiting circuit or Clipper was found in a 1977 documentation. The circuit uses only passive...