Abstract: An RF control system suitable for use in a mass spectrometer of the type having an ionization chamber, a mass filter and an ion detector. A constant frequency RF voltage is applied to the filter. The magnitude of the RF signal is varied in response to a DC control signal to permit selected ions having a desired charge-to-mass ratio to pass through the filter and strike the detector. In the control system the generated RF signal is attenuated and added to the DC control signal. The resultant voltage is applied to a comparator-integrator circuit that is arranged to provide a control signal capable of precisely holding the output of the RF generator at a predetermined peak voltage.