The traditional RF sources controllable in phase and power as klystrons, Inductive Output Tubes (IOTs), solid-state amplifiers are applicable for intensity-frontier GeV-scale superconducting linacs as the Project X CW 1 GeV linac and/or linacs for Accelerator Driven Systems (ADS), but they significantly increase the capital costs of the projects. A magnetron RF sources can significantly reduce the capital cost of the intensity-frontier projects if the phase and power control of the source is quite wideband to satisfy requirements of high stability of the phase and the amplitude of accelerating field in Superconducting RF (SRF) cavities. In the presentation are considered principles of operation and control of the magnetron RF sources and technique providing wideband phase and power control necessary to feed superconducting cavities of the intensity-frontier linacs. Last results of tests of the experimental setups of the RF source proposed for the Project X 1 GeV CW linac are also considered in the presentation.