An rf system is described which allows the acceleration of either 190‐Mev deuterons or 350‐Mev protons in the Berkeley 184‐inch cyclotron. The dee is connected to a large cross‐section line, which is in turn connected, through a rotating condenser, to a short section of grounded line of approximately the same cross section. At the upper frequency limit of 23.2 megacycles the dee and dee stem oscillate as a half wave line, while the grounded line, which is about one‐quarter wave long, oscillates in the opposite phase. At the low frequency limit of 9.5 megacycles, the whole system looks like a quarter wave line. The oscillator which feeds the system is described.