[Arran]

The broken tube looks like a 6J5 to me, or possibly some other stand alone triode tube in a "G" style envelope, 6F5 and 6K5 being two others. A 6F6 is a power pentode, though you can swap one with a 6V6 which is a beam power tube, basically a #42 with an octal base. It's possible that the tube sockets were rewired, but why? Usually the only reason to do this would be because whomever had the set could not obtain the original tube, rewiring sockets is a lot of work to do for no reason. The service info you linked shows a chassis that is the mirror image of the one in the photograph, it has the power supply sub chassis on the left, and the IF sub chassis on the right, the one in the photo is the opposite. Anyhow the two power output tubes should have the plates connected to the output transformer primary through the speaker cable, the 6J5 will not be connected to the speaker cable at all.
Regards
Arran