This sophisticated circuit with two LF411 operational amplifiers appeared in the November 1984 issue of Radio Electronics magazine. The circuit uses a Mallory buzzer as an indicator.
For reference only, this is the first IF amplifier stage of a common transistor radio from the...
This NEC commercial amplifier was manufactured in Japan in the 1960s. The circuit uses 4...
This is one of the first amplifier circuits using an integrated CA3020 from RCA in the 1960s. The...