In addition to wave properties like polarization, harmonic number, high- or low-field side launching, and launch angle, absorption of electron cyclotron waves depends strongly on plasma parameters, such as the temperature. Therefore, we have introduced a new way of operating our 110-GHz gyrotron for electron cyclotron heating and electron cyclotron current-drive experiments. In the Rijnhuizen Tokamak Project (RTP), a system for feedback control of the plasma temperature by regulating the output of the gyrotron has come into operation recently. Other parameters, i.e., the Shafranov parameter = pol + li/2 - 1, and the loop voltage can be under feedback control as well. The control system is described and some test results are given.