[en] The PEP RF system will be required to operate over a wide range of conditions, often with much heavier beam loading than in SPEAR. Since coupling loops are not readily changeable, it may be necessary to introduce other elements, such as an E-H tuner, into the system to provide flexibility for matching the klystron load requirements and simultaneously suppressing the Robinson instability. In this paper the steady state circuit relations are presented and a criterion for the Robinson instability is derived in a form which defines regions of stability in the parameter space. 2 figs