I have the original Quad II amps that I use with my old Quads (all restored)> They have almost no power for a normal speaker, but with the original Quad ESL they are perfect, better than the various ARC tube amps I used over the years with more power. I've got good glass in the Quad amps. They are very simple. I honestly never paid much attention to the circuit or what class they ran in; having them refreshed and putting GEC KT 66s in (which are probably worth more than the amps) made a huge difference in how they play. Very post war British industrial.