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 VCO circuit was obtained in the 1972 RCA linear circuits manual. The integrated comparator is CMOS and...
I found this circuit in a 1992 Electronics Experimenter Handbook. The circuit can be easily...
This audio amplifier circuit is from Ibrape's technical documentation from the 70's. The BC177 can be...