How much detail do you need?
I have the service manual for the PTU-1, but even it doesn't have any exploded drawings of the optic barrel.
http://www.myvintagetv.com/rca_ptu1.htm
I think I have a couple of spare barrels around here someplace, if no one else can supply you with a closeup I'll try to find one of them for pictures. My sets aren't anywhere easy to get pictures right now.
Chuck