A wireless power transfer system that transmits electrical power from an electrical power supply to an electrical load using a source transducer and a capture transducer. The wireless power transfer system may be part of a wireless charging system for an electric vehicle. The source resonator coil in the source transducer and the capture resonator coil in the capture transducer are substantially identical and are interchangeable. The structures that hold the resonators in the transducers and the plates that provide a ground plane for the resonators in the source transducer and the capture transducer are also substantially identical and are interchangeable. Each resonator is formed of a carrier-winder, or bobbin, that has two substantially identical and interchangeable halves enclosing a magnetic core and is wound with a wire coil.