Since my original posting I have learned that the Commander HF-2500 uses
Eimac 3CX800A7 triodes, whereas the QRO HF-2500DX uses Svetlana
4CX800A/GU746 tetrodes. Some sources have stated that the IMD figures for
the Eimac triode in a grounded-grid configuration are better than the
Svetlana GU746 tetrode in grounded cathode grid-driven mode.