The prospect of creation of the X-ray source with tunable wavelength on the base of a middle energy accelerator and oriented crystals are analyzed. It is proved, that due to the contribution of diffracted bremsstrahlung, the mosaic crystals provide the essentially greater yield of hard radiation, than perfect crystals. The method of choosing crystals with necessary characteristics in contribution ratio of parametric X-ray and diffracted bremsstrahlung in radiation yield is proposed.