This circuit was found in documentation from the 1970s. However, it can be implemented with modern transistors such as 2N2222 for Q1 and BF494 for Q2. The crystal depends on the desired frequency.
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...