folks,
in Class A operation, the tube conducts throughout the duration of the signal, and the entire signal is reproduced up to the output. this is also the most LINEAR. the primary disadvantage of a Class A amplifier is that it is inherently inefficient, and the tube is conducting all the time. Class A can be one tube, or more than one. when one tube is used, it is called "Single-Ended Class A"
when people started to seek for more power because of advertising (the numbers game), companies had to use another Class of operation, leading to Class AB.
in Class AB operation, the tube conducts more than half, but less than half the input cycle. this is used in situation where more power is needed and faithful reproduction of the input IS NOT the primary requirement. since the tube conducts at ~ half input cycle, another tube needs to conduct for the other half, hence two tubes are required, hence PUSH-PULL is mandatory for Class AB.
the key point in Class AB, is that each tube works on MORE than half of the signal. in contrast, in a Class B mode of operation each tube works on exactly half the signal. and in Class C, each tube works on LESS than half the signal, and is of little use for hi-fi audio design.
Class AB1 or AB2 is only applicable to tube amplifiers. AB1 means the tubes DOES NOT draw grid current, and AB2 means the tubes DOES draw grid current.
so, if you like faithful reproduction of the music, nothing and NOTHING, beats Class A - at the price of inefficiency.
if you're after more POWER and faithful reproduction is something you cannot discern or you don't care about, then Class AB is for you.
matter of factly, most of you go for power.
me, i have chosen my road. Class A and Single Ended Triodes.
cheers.
ps.
if you'd like to learn more about these, attend our tube 101 session this coming saturday.
