SET
really stands for "Single Ended Topology", which refers to the design of the amp and how that amp uses those tubes, not just the kind of tubes used in the amp. However it has come to mean "Single Ended Triode" by sheer force of being used that way. "Single Ended" is an amplifier design that uses a particular section of a tube--triode, diode, pentode or tetrode or any other ode for the output stage of each channel. Both pentode
and triode tubes can work single ended or in "Push Pull" designs.
A single-ended amp design uses one active part of the selected tube to produce both "half-cycles" of the audio signal. A "push pull" design, on the other hand, uses two tubes that alternate between those cycles to process the same signal and must use a phase splitter to do it.
One advantage of a single ended topology is that it creates far less higher order harmonic distortion than push pull, because it doesn't have to split and reconstruct the signal the way push pull amps do. And so with single ended designs there is no such thing as "crossover distortion".
Single ended amps always run in full Class 'A' so they drink up plenty of energy and run hot as camp stoves. And if you want much above 10 watts a side, several output tubes have to be run in parallel.
Right now I'm runing 15 watts a side in single ended pentode (which, with KT88s, is actually tetrode...but that's anoher story) and it simply kicks ass.
And that's the single-ended end of it.
-b
