Characterization from model tests of the dynamic behavior of hydraulic turbines operating off design conditions is an important step in the knowledge of instability phenomena. IMHEF at EPF-Lausanne, Switzerland meets this purpose with a standard test procedure . Simple , fast and efficient, it yields complete and easily interpreted results. This test procedure is used here to compare the dynamic characteristics of elbow and Moody type draft tubes . Relevant frequencies and cavitation compliance are expressed as functions of the machine flow rate. The runner design has a dominant influence on the occurrence of part - load resonance on the tested model. Modifications of dynamic phenomena by an internal structure of the draft tube are shown. The need for generalization of such tests appears clearly from these results.