An experimental MHD generator facility is described, in which cesium-seeded argon is used as a working medium. The heating of the gas is realized by compression in a shock tunnel. The enthalpy input into the generator is 5 MW. The test time is 5 msec. The objective of the experiments has been the achievement of electrical energy extractions as high as expected from one-dimensional channel computations. The effects of voltage drops and short-circuiting of the Hall field on the power output are discussed, and the performances of a 3ℓ and a 10I7 channel are examined. In both cases, agreement between the experiment and the theoretical model was found. The 10ℓ channel yielded an enthalpy extraction of 24% with an electrical power density of 140 MW/m3.