Apparatus for generating a control signal for a tunable circuit sensitive to temperature receives an input control signal and predistorts it in a distortion circuit, so that the output of the tunable circuit will be substantially corrected for non-linearities in the tunable circuit. The first tubular member is associated with the cycle’s frame and has a longitudinal axis. The continuous sucker rod preferably has at least two end fittings, one at each end of the continuous sucker rod.