PP VS SE - THE FIGHT OF THE CENTURY
If you're familiar with tube amplifiers, you know that the two major methods of power stage operation are single ended (SE) and push pull (PP). As with so many things in life, most people are highly opinionated when it comes to these two choices. While any confrontations between the two camps are less likely to end with blood spilled on the floor than say, vinyl versus digital or tube versus solid state (proponents of SE and PP are, after all, still "brothers in tubes"), their clashes can nevertheless be- come a bit heated at times. The real danger here exists to that poor, well-meaning soul who enters into the discus- sion and tries to play the peacemaker by extolling the virtues of each method and proclaiming them equals, which is the "raw nerve" for both camps. When this hap- pens, you'll usually see Camp SE and Camp PP rise up in unison, beat him like a rented mule and toss his limp, lifeless body aside as fodder for the vultures, and then resume hostilities as usual betwixt themselves.
Find below (PDF) a great article written by Eddie Vaughn about the differences between PP and SE amps, an the impact of these two designs on the topology of the amp and sound-quality. The second part contains an insight in the Deep, Dark Secrets of PP and SE output transformers.
Audio Note offers both PP and SE amps, but for the ultimate refined sound, SE(T) amplification is preferred (and by a large margin). As you will conclude from the article, SE(T) is hard(er) to do right, but will ultimately result in true Musical Ecstasy.