The rate of deposition of thin films evaporated from resistance heated sources was automatically controlled using a quartz crystal thin film monitor for sensing film thickness and deposition rate. Evaporation source power was controlled via a thyristor configuration and driver unit and source current stabilizer, while the overall rate of evaporation was controlled via a rate controller responding to the rate meter output from the quartz crystal oscillator mounted in the chamber of the evaporation plant. The attenuation characteristics of the current and rate loops were discussed in relation to the stability of the control. The control system was applied to the preparation of films of silicon monoxide deposited at a number of preset rates (ranging from 25 to 380 ng cm^-2 sec) in the presence of oxygen at a fixed pressure of 50 μtorr and substrate temperature of 190°C. It was shown that with the control system described repeatable optical transmission characteristics of these films could be obtained.