This circuit was obtained in a QST magazine from the 90s. The circuit makes use of components that are uncommon today. The circuit includes a gain selection switch.
This circuit is suggested by a 1965 General Electric documentation. The triac must be in...
This circuit is from the 1990 Motorola Linear Databook. The integrated circuit used is the LF355,...
This circuit from an 80's publication also features low input capacitance. FET can be a modern...