Dimebag was seen using a couple of Marshall JCM800 stacks in an early Pantera gig played in Italy in 1990. It’s also worth noting that these could also be JCM900s because it’s very hard to say anything conclusive based on the video material available.
It’s possible that Dime used these before making his dedicated live rig, which was powered by a Randall RG100HT.
it looks like they have more than 6 knobs, probably JCM900s