Capacitance multiplier (CB7803E)

We found this circuit in an old Popular Electronics. The circuit can be applied to other operational amplifiers.

Hartley Oscillator (CB19577E)
The frequency of this oscillator depends on T, which for the audio band can be a common output...
3-Range FET Voltmeter (CB25570E)
This circuit can work with almost any JFET. The circuit is from an Electronics Now from April...
Simple VCO (CB8745E)
This voltage-controlled oscillator uses components that are still common in our market. The...