In this paper, a new designed acoustic emission (AE) wideband amplifier and waveguide are used to locate the partial discharge (PD) signal in cast-resin dry-type transformer. When PD events occur in a cast-resin dry-type transformer, it is often accompanied by electromagnetic and ultrasonic signals. The AE method can be used to detect and locate ultrasonic source. However, due to the high sound attenuation in the filled epoxy, the chance to detect PD with the AE method is small. Two techniques are used to improve the shortcomings of the AE method. First, the waveguide is installed on the high-voltage (HV) windings, so that the acoustic signals of PD will propagate to the AE sensors that are installed on both terminals of the waveguide. Then the location of the winding which has PD can be detected from the difference in arrival times of the acoustic signals. The test results indicate that the waveguide technique is able to enhance safety for a measurement system and offers the advantages of easy installation and higher flexibility. Second, a specially designed wideband amplifier and filter circuit is used to acquire the ultrasonic and electromagnetic signals, which are generated by PD inside the HV winding. Using these two techniques of waveguide and amplifier not only greatly improves the sensibility but also increases the reliability of the measurement system. Field testing results show that the new techniques can be used to precisely locate the PD in HV winding.