We describe the X-ray detector which will provide second-of-arc images for the HEAO-B X-ray observatory. The instrument uses microchannel plates as a photocathode surface and imaging photoelectron multiplier, and a crossed wire grid as a two-dimensional position-sensitive detector. Position determination is accomplished by electronic interpolation between the coarse grid wires. The detector provides the arrival time and position of each event which occurs with-in its field of view. We describe our measurements of the spatial resolution (15µm), temporal resolution (7.811s), image distortion (-2 s-1), and quantum efficiency (10% at 1.54 key) of this detector. We also give a summary of the procedure which we have found useful during the initial turn-on of microchannel plates.