Abstract: A piezo electric signal generator and receiver assembly for a flaw detector has a generator adjacent to the crystal transducer and a cable connection to a distant point where a d.c. power supply and the indicator is located. The same cable is used for supplying power to the generator and for conveying to the indicator signals corresponding to both acoustic transmitted pulses and reflected returns. For this purpose a charging voltage is applied to a series circuit comprising the capacitor and crystal and this circuit is discharged by a switch connected to the capacitor at the input end of the charging circuit. Both transmitted and received signals are fed in the same direction through the cable and are therefore subjected to the same delays.