Visit the following link to learn about classes of amplifier operation.
One or more points are missing from the link provided by Gbart:
One of them is shown notch distortion in class B which barely means a thing.
It can be equal to distortions of class A due to non-linear transistor output characteristics. The larger 'range' of output is utilized the larger distortions are such as the shape of positive sine-wave may be different from the negative i.e. not as symmetric as shown. To reach the output signal 'closer' to ideal, only the small portion of transistor output characteristics can be utilized hence limiting the output power of amplifier.
In class B symmetry becomes less of the issue as long as transistors are matched or there are complex circuits of DC offset optimization between a pair of transistors.
The fact that the link above somehow explains the amplification classification (mainly for ss amps; tube amps have similar such as push-pull or single-ended) and partially answers your question should less-likely affect your opinion to the amplifier you own.
The only important facts of the amplifier should be synergy with source and speakers
Leaving theory and implementation aside, all things being equal (which they rarely are) Class A operation generally sounds better. I don't think the schematic will tell you anything, but if you turn the amp on (safest if connected to a load) and leave it on for 15-20 minutes w/o actually passing a signal thru it, you should be able to tell immediately. Amps that operate in Class A would be v warm to hot at idle. If the heat sinks or case over the output devices is only warm, its not class A. Also if the case does not have any external heat sinks, that is a clue that its A/B. For what its worth, I don't remember any Tandberg amps operating in pure Class A but its been a long time so I could easily be wrong on that one.
If your chassis gets hot during idling. It is more class A than not. If it get hotter when playing loud.. it is more class B. Class A is "on" 100% at idle, and actually uses LESS energy when playing music. Where class B is cool when idling, and gets hotter (but usually never as hot as a class A is) when playing hard.
Nearly all so-called Class A are just biased more toward class A and still go to class B when run hard. The big, true Class A are usually BIG heavy monsters that act as room heaters just being on.
So if you want a class A sound, but don't know if a amp is A or A/B, then the heat output at idle, gives a good clue.
Class D at idle is stone cold.
I too don't think that Tandberg ever made a pure Class A amplifier, and just a small minority of amplifier manufacturers have.
I suspect from your other recent post that you are referring to a Tandberg 3003, which is rated at 2 x 165 watts into 8 ohms, and 2 x 250 watts into 4 ohms, and weighs about 25 pounds.
Those figures alone indicate that it is not even close to being pure Class A. The Pass Labs XA160.5, for example, which is Class A and puts out 160 watts into 8 ohms, weighs 150 pounds for EACH single-channel amplifier. As Elizabeth said, true Class A amplifiers "are BIG heavy monsters."
Sheesh, so much doubletalk and and so many red herrings in response to a straightforward question. Here's the straightforward answer - all the Tandberg amplifiers I've ever seen are Class B (Push/Pull configuration). There is no coupling capacitor in series with the speaker, which is a dead giveaway for a Class A or AB amp. There is direct DC coupling to the speakers, which is why there's a protective relay circuit which clicks out when the DC balance is off. (Why? If you send any appreciable DC current to your speakers, you'll blow them out.) Using direct DC coupling means you don't have (another) varying impedance in the line to the speakers. (The speakers themselves are a varying impedance, but hey, ya can't do anything about that!)
Old thread but felt compelled to correct the previous statement:
Tandberg amps are in fact class AB, not class B. The outputs are not shut off completely with no signal present, which would be required to meet Class B definition.
You wouldn't be setting bias adustments at 35-40mV otherwise :-)
They made receivers with capacitive coupling (in the TR 1000 series) and without (everything subsequent to those), and they made bipolar receivers & amps and later MOSFET amps in both integrated & component form, and one receiver (3080A).
All of those are class AB.