Sent to GMU 17 September 2007. The manuscript is 12 typewritten pages and 5 figure pages. While on the faculty at University of Kansas in Lawrence, Warfield spent a sabbatical leave as consultant at Wilcox Electric Company, at which time this paper was written. ABSTRACT: Voltage tuning of filters and oscillators with varactors is becoming widely used in communications equipment, to avoid problems of mechanical tuning and to decrease size and weight. The successful use of varactor tuning over fairly wide bands requires that adequate change in capacitance can be achieved within the tuning range, that the signal developed not be so large as to drive the varactor out of its nominal range, and that the d-c voltage developed for tuning purposes be held within fairly precise limits over its range of variation. Variations in power supply voltage on the tuning system can conceivably cause serious mistuning. Sensitivity of tuning to power supply variation can be modified by padding the tuning varactor with a fixed capacitance. A set of universal design curves is given from which key design values can be obtained for most design problems involving varactor tuning. From these curves it is possible to determine sensitivity to power supply voltage changes and to tuning voltage. The use of these design curves is illustrated by an application to a differential oscillator design, where the sensitivity to supply voltage changes can be decreased substantially with the aid of the curves.