Bilateral current source 2 (CB20819E)

We found this circuit in an American publication from the 1980s. Equivalent modern operational amplifiers can be used.

Negative Ion Generator (CB25366E)
We found this voltage multiplier circuit in a Radio Electronics magazine from December 1991. The...
CMOS Crystal Oscillator (CB25578E)
The figure shows how to use a CMOS amplifier as a crystal-controlled oscillator. The circuit is...
Sound intensity indicator (CB23649E)
This simple circuit does not use active components and uses a small speaker as a microphone. The...