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 is from 2005 documentation. It automatically starts an irrigation pump when the...
Found in an old Radio Electronics, this circuit uses common components today. The resistors of the IC...
This is a traditional oscillator configuration with the 741 found in a 1980 publication. When...