GREC, an acronym for "Generateur de Radiographie Eclair" was designed for visualization, measurements and studies on dynamic behavior of materials under high explosive loading. Since the first operating time, 1975, this facility has been improved, taking advantage of progress in the techniques involved, especially focusing and transport of intense electron beams. Operating with a 2 m, 56.Q MITL,-dose levels of 250 + 50 R at a distance of 1 m from the source were routinely achieved. By employing a higher impedance MITL (free space impedance 150.E ), plasma erosion switches to eliminate prepulse and increase the input current rise time, shaped cathodes to improve pinch quality, and a low Z, thin foil over the high Z (tantalum) target, output dose levels of 550 + 50 R were routinely obtained. Using plasma erosion switches, an average increase by a factor of two in the input current rise time was observed. Spot size measurements with both 56 Ω and 1508 MITLs are compared. The direct areal masses measurement method by means of a multihole leaden collimator is described. The results obtained with the new MITL show that not only the dose but also the spectral hardness of the photon beam have been increased.