This circuit from the 80's makes use of two transconductance operationals of the time. Modern equivalents can be used. The circuit does not need to be powered by a symmetrical source.
In the figure we have the typical configuration of a Hartley oscillator. This circuit generates...
Found in an Electronics Now from the 90s this mixer has several inputs. The integrated circuit can...
This useful power supply was found in an 1985 Italian publication, but can still be assembled...