Here's an interesting and well-written article that should have the
AntiSEpTics foaming at one or more of their body orifices:

http://www.stereophile.com/tubepoweramps/196wavelength/


This bit is particularly interesting:
"Then there's the interesting issue of distortion products. SETs include
even- and odd-order distortion products in their outputs (as in nature, so
to speak), while push-pull circuits cancel out even-order distortion by
design, leaving only the less musical odd-order products intact. Now
look...there's something to this. It's suggested that the sound of
single-ended triodes has much to do with their delivery-intact-of the full
spectrum of distortion products. "More distortion is better?" I hear you
ask. Well, it's less humorous than it sounds. Might "unnatural" proportions
of odd-order distortion account for part of the sound of push-pull?
Something to think about."

.... and should be read by those here who are continuing to confuse the
radically different terms 'realistic' and 'accurate'..