This oscillator that generates signals below the audible range (sub audio or infrasound) was found in a 1965 documentation. Transistors are for general use.
This circuit was obtained in an English publication from 1993, but it can still be assembled with...
The input impedance of this amplifier is of the order of 1014 being the same indicated for pH...
This filter is current driven and has the formulas given by the two diagram options. The circuit...