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.
Found in a 90s Popular Electronics, this circuit allows to select the operating ranges between...
This circuit was obtained in a 1960 transistor manual from Sylvania. The circuit uses small...
This simple unijunction circuit is from a Radio Electronics from July 1963. It can be assembled with a...