Two ICRF generators, previously used for ASDEX and W7-AS, have been designed almost 30 years ago [1], based on technology and components available at that time. Four, more recent generators used by ASDEX Upgrade, are an evolutionary development. Today, two out of three tetrodes used in the amplifier line up are obsolete and spares are becoming scarce. Based on the long experience gained with the initial configuration, a redesign process has been started aiming to significantly prolong lifetime of the generators. Each of the four amplification stages required to reach 2 MW output power is undergoing a more or less severe modification. The most critical change concerns the final amplification stage and has already been successfully implemented [2], whereas changes of the remaining stages are on-going. A new, FET based first stage, provides a higher output power in order to drive the following (pre-driver) stage where a triode is replacing the initial tetrode. The tube of the third (driver) stage is upgraded to a higher power dissipation capability, to increase the drive power for the fourth (final) stage. One of the two generators formerly used for ASDEX and W7-AS has been modified along those lines.
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