A magnetostrictive transducer assembly for generating a longitudinal elastic guided wave of a selected frequency and mode and for guiding the wave into an open end of a heat exchanger tube for testing the tube. The transducer assembly comprises a current-carrying coil of wire, a magnetostrictive material wrapped around the coil of wire, a mechanism for pressing the magnetostrictive material against an inner surface of the tube, and one or more biasing magnets placed in the vicinity of the current-carrying coil of wire and the magnetostrictive material.