Haha it is the vox ac tone that is the signature tone of many famous guitarists! All i can say is that the amp itself is legendary, it is like saying "the marshall tone", "the fender tone", "the mesa tone"........etc. Basically the vox is very famous for it's really nice full chimey clean tone.......if fender is the clean tone of america.....think vox as the clean tone of britain keke. But it has a very nice and distinct cranked tone as well......very meaty and sizzle....especially those AC amps with the top boost channel!
As for achieving clapton's cream days tone......if u r a purist, u can only get it with a cranked up marshall plexi or a bluebreaker, accompanied with a LP, SG or ES type guitars (gibsons r the sure way, but not the only way). But the most essential thing is not the equipment, instead understanding his techniques that shapes his sound is the key bro!