Found in American documentation from the 90's, this circuit is very current and can be implemented with transistors of general use. Never use a power supply without a transformer.
This circuit was obtained in an Electronics World of 1969. It is a crystal oscillator with a 100...
This circuit, shown in the figure, consists of a variable gain amplifier with differential input...
This circuit was found in the July 1992 Radio Electronics magazine. Sensitivity adjustment is made...