Sinusoidal Oscillator 741 (CB8426E)

Found in a 90s Popular Electronics, this circuit uses a 741 to generate frequencies from 0.1 to 30 Hz. Observe the phototransistor feedback.

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Telegraph Practice Oscillator (CB6474E)
Found in a 1965 Radio Shack documentation this oscillator can be used with modern general purpose...
Dual Tuning Circuit with Varicap (CB13344E)
In the figure we have the way to use a single control voltage to act on two varicaps...
Sensitive touch switch (CB9561E)
Found in a 90s documentation, this switch that is also sensitive enough to operate capacitively uses...