This commercial circuit is from a Japanese magazine from 1967. It uses germanium transistors, and the coil can be made with 80 to 100 turns of fine enameled wire on a ferrite rod.
This circuit is from the 1990 Motorola Linear Databook. The integrated circuit used is the LF355,...
This high impedance amplifier is from 1985 documentation by General Electronic. The amplifier with...
Based on the TCA6600 or TCA5500 this circuit was found in a 90’s European documentation. The...