This resource was developed by Mesa Engineering. Mesa Boogie amps are some of the best tube guitar amps on the planet.
So what is a Class A tube amp and how does it differ from a Class AB?
The most important thing for a musician to understand is that the different amplifier Classes and Configurations serve different purposes and styles. No one is flat-out better. A player looking for maximum clean headroom will want a Class AB, push-pull amplifier because power is its forte. A player seeking a certain vintage vibe may prefer a Class A amp, but no matter what tube is used, it will definitely be less powerful. Either type can be made to sound warm and lush or brash and biting – mostly as a result of other important factors such as the pre-amp and driver circuitry, transformer and component choices and, of course, speaker options.
The previous material was written in 2005 by MESA Founder, Randall Smith. Click here to download and read the full article (with illustrations & examples).
If the original source linked above is down, you can also download this copy of Class A vs AB from Mega Distortion.