Keep up the good work. This is the most fun reading I've had on the subject of tubes. Your math looks very good to me, and your explanations are lucid. I don't know how anyone can argue if they actually pay attention and think. Maybe that's too hard, having your mind already made up is easier.TJ   Once, I thought the 5% distortion limit to measuring an amplifier's output wattage a little too arbitrary: Why not 1% or 10%? Today, I embrace it wholeheartedly. And I would argue that we need a 20% rule for determining the Class A  to Class AB transition point. We know that the advantage Class A enjoys over Class B is the flatter output impedance across the entire waveform that derives from both output devices working equally hard. Thus, my definition of Class A being simply the mode of operation wherein both devices continue to conduct over the entire waveform does not go far enough. It needs to be restated as "Class A is the mode of operation wherein both devices meaningfully continue to conduct over the entire waveform." When does an output device stop making a meaningful contribution to the power output? We could arbitrarily pick 20%, or even 50%, as the distortion limit to current waveform through the device. So that once this figure is exceeded, the amplifier is considered to be operating in Class AB.  It has been said that the world divides into two types of people: those who believe the world divides into two types and those who don't believe it does. With audiophiles, I have found the two types to be those who like math and those who don't. Of course, some go much further than just not liking math. I remember one audiophile asking what wattage the plate resistor in his amplifier needed to be and being disgusted