You might reflow the solder connections on all the PC board tube socket terminals. I usually add just a tiny bit of solder while doing this to help the heat to conduct and to bridge any cracks/breaks in the soldering. As mentioned above you should check the entire filament string with a meter, including continuity of the each tube filament too with a little expected resistance there of course.
Page 3 of the SAMS on this shows the filament string detail. Here is a link to the entire 21 page PDF:
http://www.earlytelevision.org/pdf/P...Sams-439-1.pdf