A combination includes an AC power system and a system for improving power factor in the AC power system by continuously variable, analog control of level of reactive current introduced into a power conveying line of the AC power system. A power factor-improving circuit includes at least one channel that comprises a channel-level AC electron tube circuit and at least one associated reactive impedance element interconnected in series manner. Each of the channel-level AC electron tube circuit is responsive to a control system for continuously variable, analog control of the level of reactive current in the at least one associated reactive impedance element so that the foregoing level of reactive current changes, as necessary, in a continuously variable, analog manner to improve power factor in the power conveying line. Each of the channel-level AC electron tube circuit comprises at least one cold-cathode field-emission electron tube.