It is modelled after the Marshall 50W Plexi. I think the designers had "Smoke on the water" in mind when they did that one.
One interesting thing about that amp model is that it has a great clean tone to it.
Set the gain as high as you can WITHOUT any breakup, bring the volume up to how you want it and then adjust EQ to taste. I drop the Bass and mids abit and bring the treble up.