The 300B on that side isn't drawing any filament current, as can be seen by having 0V on terminal 16. If you have 10V or so at POS OUT on that side, then you should have 10V going into the 300B, passing through the 300B filament, then traveling through the paralleled 8 Ohm resistors.
This could be an issue of an improperly oriented 4 pin socket, or no voltage at POS out. (Go ahead and measure it)
-PB