This sophisticated filter for audio signals was found in Radio Electronics magazine. The frequencies are determined by LC circuits. The circuit has selectivity selected by a switch.
This circuit from a National Semiconductor manual from the 1980s shows how to use the LM388, a...
This is a circuit with a new (at the time) component released by Raytheon in 1965. The circuit uses a...
Suggested by General Electric in a 1970 documentation, this circuit makes use of some components of...