BEAM-POWER TUBES are also used as power amplifiers. In addition to the in-line grid
arrangement, beam-power tubes use a set of negatively charged beam-forming plates. The beam-forming
plates force electrons that would normally be deflected from the plate back into the electron steam and,
thus, add to the number of electrons the tube can use for power amplification.
VARIABLE-MU (µ) TUBES or REMOTE-CUTOFF TUBES were developed to extend the
amplification range of electron tubes by avoiding the possibility of driving the tube into cutoff. This is
done by uneven spacing of the grid wires.