The use of a detector bridge instead of a single diode, as is normally done in common galena radios, allows to increase the sensitivity and, consequently, the volume of the sound obtained in the headphones. The circuit, very simple, uses 2 diodes and 2 470 pF capacitors in the detector bridge, in addition to the parts common to other radios of this type. The L1 coil should have 150 turns of enameled wire 27 or 28, in or near a 38 mm shape. The variable capacitor is of the common type for medium waves, and as an antenna one must use at least 10 meters of wire. The author used, with good results, a 14-meter-long antenna. Grounding is very important to obtain good reception. A high impedance magnetic earphone (at least 1 000 ohms) must be used at the output, crest headphones! or, even, an output transformer with a low impedance phone or small speaker.
