Yes the aiken amps article is excellent and the opening statement above is related to my point and can be applied beyond the ac30 to any clas ab as it states. This is a little understood aspect of this topic and I am simply saying the ac30 stays in class a longer due to its hotter bias, for a given output in a comparison. And once again, if run before the onset of clipping, which occurs later in an ac30 in comparison to a marshall push pull class ab design with a colder bias, this makes comparing the 2 a reasonable example within reason once again, below an established output. Not taking offense but your misunderstanding because of my inaccurate statement and I believe that class a is a factor in a watt for watt comparison, the vox stays there longer. Many dont realize that that just above bedroom tone their amp is in class a, its the beauty of the tube amp. Translated another way in a practical sense is any amp turned up for stage level to where the output stages clips with the guitar pot up is in class ab and rolling it back is not driving the output stage into class ab. When you think about how to use this it becomes obvious that the guitar pot is bascially controlling more than just overall volume and it becomes a useful tool in getting tones, tones that are sweeted some, absent of crossover distortion and clipping the output, allowing the even order emphasis in the triode staged pre-amp be more apparent. Of course there is cancellation in the output stage and to what degree could be the subject of a nasa study. In my example, if comparing a ac30 to a comporable traditional fixed bias pp ab design in a watt for watt comparison given other factors, the vox will deliver more useable travel on the guitar pot to the onset of clipping. That is why I suggested it would make a good comparison and is where my opinion is rooted. I have compared my 30 watt rivera with a buddys ac30 and can hear this when the amps are set roughly for the same level, in the rivera some clip creeps in with a slight crunch and imo is in class ab sooner where the vox is fat and round with that sweeted chime, still in class a. I think its a valid comparison. Now I can appoximate the vox tone with the rivera using a compressor set to squash and limit slightly and bring on some mid and high end chime at the same time to where its as loud but yet cleaner if you will. With the compressor off the output on the rivera has that characteristic crunch as the limiting is bypassed and drives the output harder, imo the output stage gets pushed into ab and with it on its in class a, I am hearing the transition and thats what I believe. In combination with the guitar pot, preventing the rivera from being driven into class ab, I can get it at a stage volume. At this point its departing from the natural character of fixed bias class ab amp to a point where it has to be driven harder/louder to get into ab and when you think about class of operation in a tube amp, you soon realize its the magic of the tube amp, the ability to control the transition of class of operation. To some degree simplisitcally, its a matter of dialing it in or out, class that is.