For the solar panel (BP), use a ready-made unit measuring approximately 35mm × 10mm, with an open-circuit voltage of ≥2V and a short-circuit current of ≥8mA. Integrated circuit A is the YS414 model; interchangeable equivalents include the D7642, TA7642, CTC7642, YS7642, BS414, MK-484, and 2N414. Transistors VT1 and VT2 should both be 9014 or 3DG8 type silicon NPN low-power, low-noise transistors; the current gain (β) for VT1 should be between 40 and 150, and for VT2, between 20 and 60. The ferrite antenna coil (L) must be wound manually using 0.15mm diameter single-strand high-strength enameled wire; wind 82 turns in a single, tight layer around a 5mm × 35mm medium-wave ferrite rod. For capacitor C1, select a 5–200pF ultra-miniature sealed variable capacitor; use CT1 ceramic capacitors for C2, C3, and C6; and use CD11-10 electrolytic capacitors for C4 and C5. Resistors R1 through R5 should all be RTX-1/8W carbon film resistors. For potentiometer RP, select a WH15-1A miniature carbon film potentiometer without a switch. Use a CKX2-3.5 two-contact jack for XS, and an 8Ω low-impedance earphone equipped with a CSX2-3.5 two-contact plug.
During adjustment, tune the resistance of R3 so that the total current consumption of the unit is approximately 4mA. If the reception frequency range does not cover the medium-wave band (535–1605kHz), calibration can be achieved by shifting the position of the antenna coil along the ferrite rod. Thanks to the use of a dedicated integrated circuit like the YS414, the circuit is simple to construct and generally requires no complex adjustment. The casing can be fabricated from plastic sheet material.