The present invention relates to a composite amplifier (3, 4, 120), a radio terminal (100) including such composite amplifier and to a method for improving the efficiency of such composite amplifier in particular. The composite amplifier according to embodiments of the present invention is arranged to be connected to an output combiner network (43, 53, 63, 73, 83) and to a load (49, 130). the output combiner network comprising at least one dynamically tuneable reactance (47, 48). The instantaneous efficiency of the composite amplifier (3, 4, 120) is increased by tuning the impedances/admittances seen by each of said at least two power amplifiers (41, 42, 71, 72). The amplifiers being differently driven and they may further be part of a Chireix outphasing system or a pair of a Doherty amplifier.