[en] We describe a soft X-ray detector having a 20x20 cm² active area and constituted by a conversion and drift space followed by a parallel-plate avalanche chamber. Bidimensional localization of the detected charge is performed on the last electrode recording the pulse-height profiles of the fast electron-induced signals on a two-sided thin printed circuit with orthogonal sets of conducting strips at 500 μm pitch. Localization accuracies of around 120 μm rms are obtained in both directions for 8 keV X-rays. It has been observed that, whilst the induced charge on the side of the board internal to the chamber (the anode) is negative (as one would expect), the charge seen by the pickup electrode on the back face of the readout board is positive, much as it would appear on the cathode of a multiwire proportional chamber. Because of its very good two-cluster resolution, one can envisage the use of this device in transition radiation detectors. (orig.)