If you go here: http://marshallampforum.com/
I'm sure you will find someone knowledgable enough to answer your question. Try the "Workbench" section.
I am pretty sure that the preheaters are supposed to glow, I know my TSL100 does, so I don't think I'd play the amp until sure.
Good luck.
Hey thanks,I saw that forum last night ,This is my buddies amp I thought I would take a look at it ,the internal fuse was blown and to late to get replacement.If if blows again he's on his own..............Jason