A new electron beam source was developed according to ultrahigh vacuum design rules. It is rate controlled by means of a quadrupole mass spectrometer based flux meter. Preprogrammed and stored wobble patterns with a large frequency range prior and (for most materials) during evaporation improve the performance of operation and enable a high utilization of the material. A very stable operation is achieved by simultaneously controlling not only the power but also the power density. Long term stability, material utilization, dynamic range, minimum controllable rate and reproducibility were investigated especially for Si molecular beam epitaxy.