Found in a 1960s RCA manual, this circuit uses components from the era. For the indicated circuit R1 is 28ohm and R2 is 1 k.
In the circuit of the figure, when pressing S1 the sound varies according to the value of R2 and...
This switching circuit for contact breaker cars was found in a Radio Electronics from April 1964....
This inverter amplifier is from a 1992 publication. NPN transistors can be BC548 and PNP BC558....