[quote=Marcus Black] What makes a piece of gear Class A,

the very simple view is the components in the circuit have only one voltage rail ... when the circuit is stationary it is held at the half way point and there for have an offset voltage

yes I know an op-amp can operate of one rail but internally there are voltage dividers

lots of inaccuracies in there but I'm trying to give an overly simple look

.. what requirements does it have to live up to ?

errr
strange way to ask the question
http://sound.westhost.com/class-a.htm
look to the chart and the section just below the chart
thanks to Rod Elliot

.. And Class AB ? Class B ?

again see the above
the unit will have a pos and a neg power supply
the unit has to swing into the pos and neg world each time it goes through 0 volts ... this cross-over the 0 line can be a source for error ... crossover distortion Class B
When you get each side to drift into the other rail and make the cross-over smoother ... less distortion (use bias) we have Class AB
a bit of A and a bit of B
It is possible to have complete overlap and have the pos section and neg section always conducting ... still ClassAB and very inefficient but some think very linear or symmetrical ... sorry getting off track

Is solid-state simply a design without tubes ?

yep

Discrete is point-to-point-wired with no IC's or...?

no integrated circuits
discrete or individual components

point to point is the use of wire and not PCB ... printed circuit boards
mostly a tubed world

For example the 1073 is discrete and Class A but the 1081 contains Class B electronics, what´s the major difference ?

the output driver of the 1081 is ClassAB and so it does not require the gapped core output transformer which is large and expensive ... well so they said
The AB produces less heat and probably less distortion

And then I read an interview with a designer talking about "REAL Class A"-stuff, not just Class A. Could someone straighten this out for me once and for all, thanx.

ouch
some of it is hype and some of it has route in definitions
before i jump
which designer and I'll try to get to the point rather than go in circles

I´ll try to add a few words about class A. You might believe that class A has something with quality to do, but it does not. The fact is that class A is simply one way of setting up a circuit. The deciding factor is that the transistor (or for that matter other devices such as tubes) conducts all the time. In other circuits the transistor may shut down at parts of the wave-form.

You may see some explanations here:

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part2/page2.html

So you might ask if class A is better than class B? No, that is not why they are called A or B or AB or whatever. That only describes how the circuit is constructed.

So does class A sound better than class B? No, it might, or it might not. It depends on so many other things. There are some people who can swear that class A is the only way to go, but you might also find other people swearing that silver loudspeaker leads is the only way to go. Are they right? Only way for you to know is compare actual equipment using your own ears. I at least have built several class A circuits that sound really awful.

Gunnar.

Thank you, great replies !