The CA3020 integrated circuit was one of the first commercial types, sold in the 1960s. The circuit presented is from 1968 using a power stage with RCA transistors of the time.
Found in a Popular Electronics from the 90s, this circuit operates up to about 5 MHz input....
This circuit was found in a 1987 edition of the United States' Hands-On Electronics magazine. The...
This circuit that uses potentiometer tuning, was found in a documentation from the 80's. The...