This AM receiver circuit is based ob the IC ZN415 introduced by Ferranti. This IC is an improved version of the early ZN414. It is a complete AM radio receiver and does not need IF transformers and alignment. Integrated in the IC is the early ZN414 and an audio amplifier circuit.
The tuner stage civers the frequency are from 150 kHz up to 3 mHz. It is designed to receive MW and LW signals. The audio output is around 1….1.5 Mw at 64 ohm load. The IC comes in an 8 pin DIL package. Originally, a headphone is enough to enjoy the functionality of the receiver but is sounds better by adding an external audio amplifier than can drive an 8 ohm speaker.
The circuit however needs 9 volts supply in contrast to the IC which needs only 1.5 volts. The power output of the amplifier circuit is around 10 mW.
The headphone can be left connected to the IC while the external amplifier works since it is connected to a separate oin of the IC. If the circuit is to receive MW signals, the coil L1 must be 65 turns of antenna wire around a 600mm x 12mm x 3 mm flat ferrite bar. If it is to receive LW signals, the coil L1 must be 300 turns of antenna wire around 150mm x 10mm ferrite rod.
The coil for MW operation is wind in a single layer. The coil for LW operation can be wind on top of each other. To enable reception on both frequency bands, a 10pf capacitor must be connected in parallel to the LW winding. A switch must then be used to select the necessary coil.