This circuit tunes MW radios to apply the signal to a good audio amplifier. The circuit is from an old documentation. Transistors are general purpose types.
This low frequency square wave oscillator using the 741 Operational Amplifier produces sound when...
This small preamp for low impedance microphones was found in a Popular Electronics from November 1968....
We found this circuit in an old American documentation. Transistors can be modern equivalents. ...