When he says "Power is 40 watts at 50% triode operation with the standard EL34s; 45 with KT88s; and 50 with KT90s." I think he means that he is only using half of the triode tube. There's a little more information here. I don't *think* this means 50% power but I'm far from an expert on tubes. Maybe somebody with more knowledge will jump in.
Dick
Dick