This circuit uses a parallel resonant crystal to control the frequency. The circuit is from Radio Electronics magazine, February 1993. Equivalent transistors can be used.
This circuit matches a source of high or medium impedance audio signals with a low impedance...
Found in a 1993 Electronics Hobbyst Handbook, this circuit uses components that are still common...
This pulse width-tuned circuit was found in the March 1996 issue of Electronics Now magazine. The...