Thanks, we may be getting somewhere. I traced the negative voltage from the 6DQ6 grid, along the path you described, and it all looks reasonable until I get to the junction of the 100-ohm resistor and pin 3, so possibly something is funky there -- a bad solder joint, cracked trace, or bad socket . . . . I'll investigate tomorrow when I'm feeling fresher.
I recently got the Philco service manual, which is better than Sams in some ways. For instance, it has a wonderful diagram of the main circuit board, with a list of what all of the perimeter connecting wires are connected to -- something I had laboriously drawn by hand in the past.
I scanned the Philco schematic (in two parts) in case anyone might find that helpful:
http://antiqueradio.org/art/Philco10L4xSchematic1.jpg
http://antiqueradio.org/art/Philco10L4xSchematic2.jpg
An advantage of using the Philco docs is that the part numbers (and other IDs) match those printed on the circuit board.
Regards,
Phil Nelson