A control system that tunes the resonant frequency of a lightly damped resonator to its excitation frequency in the face of detuning disturbances is investigated. The resonance tuning is achieved by adaptively controlling the resonant frequency of the resonator using the error between the excitation frequency and resonant frequency. Assuming that the parameters of the resonator are slowly time-varying, a nonlinear time-varying model that accurately predicts the tuning performance of the system is developed. This developed model is subsequently linearized to obtain a linear time-invariant model that facilitates both analysis and design of the resonance tuning system. Based on the developed linear time-invariant model, guidelines for designing the resonance tuning system are provided. The results are illustrated by examples.