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I saw James Peters below answer this a bit, and his answer is pretty spot on.
I'd like to add a touch though. Class A amps that are single ended with one tube do not need a matched phase inverter. There is nothing to match, and there would be no benefit.
In class A amps that use an output pair, such as Dr. Z amps and Vox, Matchless, etc ... these Class A amps, when driven at mid to high levels, operate in push-pull, or class A/B. A matched phase inverter, which in this case is really an output driver, really helps these amps. In Dr Z. amps it makes them even nicer. In Vox AC-30 amps is seems to make the output tubes last longer as they seem to be under less stress from imbalances. I am still trying to study this and figure out why from a scientific standpoint
If you want to forget all this "amp tuning" and amp "blueprinting" trouble, and just have a geat amp, then go to the guy that I listen to and learn from .... James Peters His amp is a super product, and if you need to play a gigantic venue, use a open back 1x12 cabinet and mic it ... throw it into the house system with a few mega watts of amps, and now you will have terrific tone and sound that you can control, rather than the 100+ watt amp that is trying to control you (and that sounds it's best at only very high drive levels).
Regards, Myles-
Many thanks for thi info, as always. I am looking for a 1x12-is Mr. Peters online? I`d like to see what`s available.