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This paper describes a new high-efficiency modulating system in which carrier is supplied by a single tube acting as a class C amplifier. This tube drives the load through an impedance-inverting network and becomes, in effect, a constant-current generator. A second tube, working directly into the load, is operated as a class B amplifier, and is excited with a signal consisting of both side bands with carrier suppressed. For upward modulation, the second tube has an output in phase, at the load, with the first and delivers additional current to the load. For downward modulation, the second tube has an output in phase opposition, at the load, to that of the first and absorbs current which would otherwise be delivered to the load. The use of biases to improve further the efficiency and to reduce distortion and the use of envelope feedback to reduce distortion are described.