This VCO with discrete components was found documentation from the 1980s. The central frequency with the indicated components is 8 kHz. A BC548 can be used for Q1.
This circuit appears in similar versions on this site. This is from a Popular Electronics from the 80's. The...
This two-transistor delay circuit from the 1960s was found in documentation from the time....
This circuit operates with signals from 150 kHz to 1 MHz and makes use of a known NAND CMOS gate....