Pretty sure Bob's right. Check out this carbon mike:
http://www.oobject.com/classic-micro...crophone/1468/
The tube socket may be for early short-pin UV prefix bayonet pin tubes. I don't have one to compare, but a UX-199 which is a little later has a 1-1/8" diameter base. I think the WD-11 and similar were a little narrower in the base.