I posted this on another forum and though it might be useful here for reference?
Here's a brief and simple/basic rundown of Marshall amp history. (I'll avoid all the minute details and keep it general):
JTM45. Original offset head model. Black tolex with silver grille cloth. 1963 to 1965ish. Based on a Fender Bassman. Two KT-66 output valves. Valve rectifier. 45 watts.
JTM45 MKII. As above, but with the more recognisable 'old Marshall' style cosmetics. 1965 to 1967ish. Same amp internally as above. The Clapton 'Beano' sound.
JTM45/100 or JTM100. 100w version of the JTM45 with four KT-66 output valves. 1966 to 1967ish. Very rare amp as used by The Who, Hendrix and early AC/DC.
JMP Lead (50w - model 1987), Superlead (100w - model 1959), Bass (50w - model 1986), Superbass (100w - model 1992). Usually referred to as a Plexi. Output valves switched to EL34s, two for a 50w and four for a 100w. Solid state rectification. 1967 to 1969. The start of Marshall as most people know them. Bass heads have the same preamp as the JTM amps. The Lead heads have a more treble biased preamp. Used by AC/DC, Eddie Van Halen, Free etc.
JMP non-Master volumes (ali panel versions of Plexis, same model numbers). 1969 to 1981. Essentially the same amps as the Plexis, but less collectable.
JMP Master Volume (50w - model 2204, 100w - model 2203). As the plexi amps, but Lead heads available with master volumes. 1975 to 1981. Used by Thin Lizzy.
JCM800s (same model numbers as the Master Volumes). 1981 onwards. Cosmetics changed to the modern Marshall style, same amps as the ali panels. Used by Zakk Wylde, Kerry King and most 80s rock bands.
Silver Jubilees (50w - model 2550, 100w - model 2555). 1987-1990. Released for the 25th Anniversary of Marshall amps and most came in silver tolex. Based on the JCM800 but with a solid state extra gain stage in the pre-amp (like a built in overdrive pedal). They also have a half power switch. Used by Slash and Joe Bonamassa. (The Slash signature amp from a few years ago is essentially a Jubilee re-issue)
Sounds?
JTMs have the best clean tone (it's essentially a Fender amp.....). Lots of bass and a smoother overall tone. Great blues amp, and a rocker if you add a pedal in front. My favourite Marshall, and I gig a JTM45 clone.
Plexis and the non-master volume ali panels sound broadly similar. More aggressive than the JTMs with more gain, bite and treble. The sound of rock since rock began. They suffer on the clean tones and as such need to be cranked to really shine, then they are awesome. Not the most versatile amp, more of a one trick rock pony.
Master volumes/JCM800s sound pretty much the same. Very pre-amp biased gain and are again the sound of rock. More flexible as you can dial in gain at lower volumes, although they can sound a bit 'fizzy' if you do this. They have a bit more gain the non-master volume amps when you crank the gain dial. Crank the master volume up and these are also awesome amps.
Jubilees do have a sound of their own due to the tweaked pre-amp, but they sound broadly similar to a JCM800.
Summary?
Need a clean tone and lower volume? Get a JTM45 (or a clone) and a pedal or two for gain. The Blackstar HT Dual works well here ;)
Need plenty of volume and gig blues/rock on large stages? Get a non-master volume Lead or Bass head (or a clone) and crank it. Only go for the Super heads if you play BIG venues.
Need plenty of volume, plenty of gain and gig rock/metal on large stages? Get a master volume/JCM800 head (or a clone) and crank it. Again, only go for the Super heads if you play BIG venues.
Jubilees are a taste of their own and can/have been used for blues through to heavy rock. They're a "try it and see if you like it" amp although their rareity means they're expensive.
Here endeth today's lesson in Marshalls :)