The channel sw. 800's do have diodes on the boost channel, but not the normal channel. But there is much confusion about these, since Marshall made the largest and most radical design change in these around 1985. The tone change is huge.... most prefer the later versions for OD, but some prefer the early ones. So best to just judge for yourself.
There are more opinions on these than any other Marshall made. Since very few know about the design changes, opinions are based on whichever version they hear. My personal opinion, and mine only!!!, is the early version Marshall ch. switchers are the only Marshall ever made (including the Valvestate, MG series etc.) that I would never in a million years gig with.... What I do gig with is an '89 ch.switcher....diodes and all! It remains my absolute favorite amp ever made...out of any... even amps that aren't Marshall. You can see why opinions are so varied on these....
I can tell you how to tell the difference, but I would just try it out and draw your own conclusion.....
Jeff Seal