Class A?

Can someone please help explain to me what a Class 'A' rating on an amp means? What are the other ratings? If you know of a recomended source to explain this I would love to know.
Thank you in advance!
In simple terms Class A means the output devices (solid state or tubed) are kept switched "ON" regardless of audio signal input from the amp driver stage to the output stage. That is why Class A amps run "hotter" than Class A/B or Class B where the amp is really only drawing current when there is an audio signal passing thru the system. There are some good reference sources on the web, have a search on MSN under "Class A amplifier bias" and you should find something a bit more technical. Hope this helps, regards, Richard
Richard is, of course, correct, but just to verbalize a little more... so, the "class" is not a rating, it is the characteristic of the output stage design. There are several defined classes, but A and AB are considered "linear"; that is, there is relatively little distortion of the input signal when amplified and that is why they are appropriate for audio amplification (AB also used for SSB radio, if you are interested). Generally that is because the initial operating point (determined by bias in tubes and base-emitter current in SS devices) of the devices is set so that all output current change driven by the input signal occurs in the linear portion of the device's characteristic curve (a property of each device type). Class A is the most linear and its initial operating point to accomplish this is such that there is higher no-signal (idling) current. Other linear classes do also have no-signal current, but less than class A. Some trade offs in the design choices for equivalent devices are that class A proves least distortion but lower power (because no-signal current is closer to max current) and probably hotter running because average current is therefore higher. I hope this doesn't conflict with any more authoritative source. :)
Please read that ... "provides least distortion"
"Class A" is also used by Stereophile in their recommended component ratings. You may occasionally see an ad for a component that describes it as "class A", and that may be referring to Stereophile's recommended components list, not amplifier design.
So there must be some Class A Class A amps and some Class B Class A amps and so on. Only in Audiophilia. Sorry, I couldn't resist. :)
Sndsel, Just cause it runs in class A doesn't mean its better than class a/b or b. Just wondering cause I tried a class A amp(plinuis 100) on my martin logans and then I tried a bat vk200, I used the bat 3i pre with both amps. The bat vk200/3i killed the plinuis/3i combo. I really wanted the plinuis to smoke the vk200 and I expected it to cause 3people from the audio store said it should, but it didn't. Is it cause the plinuis is not stable down to less than 2ohms, were the bat is. I read my martins needed a stable amp. I could have bought the plinuis for the same as the bat, but the bat was better so I bought it. Any insight on this. When I took the plinuis back and kept their bat the guy at the audio store was shocked.
Class A is not just output stages. It can be but many components are Class A input to output.