CCR completed assembly of a new, high efficiency RF source for driving superconducting accelerator cavities. The system uses a high efficiency magnetron that is phase locked for precise frequency and phase control. Amplitude control is achieved in real-time by phase modulating the locking signal. This allows feedback control of the magnetron phase and output power. The prototype system is designed to produce 100 kW at 1.3 GHz. System testing is scheduled for spring 2017.