V1 (a and b): It's the one closest to the input jack. It is responible for providing to initial gain stages. It also provides so tone shaping, this is fixed tone shaping as opposed to the tone stack which we'll get to later. The preamp volume control usually sits between these gain stages. V1b provides some signal gain and the preamp volume controls the amount of the this that passes to the second gain stage V1a. V1a in turn directly feeds V2a.
V2 (a and b): V2a provides more gain and some tone shaping. The legendary Plexi bypass cap (.68uF) is at this stage. This stage is fed directly to V2a which is a "cathode follower". This stage provides no voltage gain but intead gives a low output impedance in order to drive the tone which follows. This give you the standard bass, mid, treb controls that we're used to. The stack then feeds the master volume. This controls the amount of this signal feeds onto the phase inverter.
V3 (a and b): The phase inverter provides two distinct outputs, one of them is 180° out of phase with the other. This is required to feed either side of a push pull power amplifier stage which, AFAIK, all Marshall use.
...mais sur une pancarte juste à côté d'une table, c'est marqué "interdit les punks et les arabes"...
