 Class A refers to the amount of current flowing through the power tubes with zero audio signal, with Class A meaning maximum current flow even with zero signal.This makes the tubes run hotter, and gives the power section even more gain at the cost of tube life and noise.The Class-A designation for guitar amplifiers is often a misnomer; Few amps outside of the heralded Vox AC-30, also with cathode bias, operate in a true Class-A mode [Albeit, it only did so up to ≈21 watts RMS].