Design and procurement of the ICRF heating plant for JET began in 1982 on the basis that ten 3 MW generator-antennae units would ultimately provide the 15 MW of effective ICRF heating required in the JET programme. Three of these generator-antennae systems are already operational on JET; 6 MW of RF power has been coupled to the plasma with coupling efficiencies of between 50% and 90% depending on the antennae configuration. Taking advantage of experience gained and recent developments in RF tetrodes, JET is currently revising the antennae design, upgrading the generator RF outputs and now intends to install eight 4 MW generator-antennae units with consequential savings in cost and space in the JET vessel.