Example to explain:
Class A: If amp peak current is 10A then with no signal all 10A flows thru the + rail transistors also the - rail transistors and none thru the speakers. At half power 5A flows thru the speakers and 5A flows thru 1 of the transistor rails while 10A flows thru the other (depending on polarity of signal).
Class A-B: If peak current is 10A, then with no signal maybe only 1A (amount can vary according to how heavily biased it is) flows thru both transistor rails and none thru the speakers. Above 1A of speaker current one transistor rail turns off and the other carries the full speaker current (which rail depends on polarity of signal)
Class A: If amp peak current is 10A then with no signal all 10A flows thru the + rail transistors also the - rail transistors and none thru the speakers. At half power 5A flows thru the speakers and 5A flows thru 1 of the transistor rails while 10A flows thru the other (depending on polarity of signal).
Class A-B: If peak current is 10A, then with no signal maybe only 1A (amount can vary according to how heavily biased it is) flows thru both transistor rails and none thru the speakers. Above 1A of speaker current one transistor rail turns off and the other carries the full speaker current (which rail depends on polarity of signal)