I dont have the manual BUT this is how its probably wired.
The twisted pair of brown wires to the CRT are the filament.
They probably go to a separate winding of the power transformer.
There will be a fusible link in series. I have never seen one go except
when they are the line fuse. The filament is above ground & usually
"rides" on abt 150VDC to keep it near the cathode voltage.
1) carefully remove the socket. On old sets with bakelite on the CRT end
hold that & rock it off. If stuck slowly pry with a little screw driver.
2) measure the 2 filament pins for 6.3 VAC. If the 6.3 VAC is there its the
CRT socket or CRT. If not there its down on the chassis.
3) common problem is the CRT gets gets cold joints where the CRT wires
come into the pins. Resolder them but only the filament ones for now.
They go intermintant & cause the pix to fade in & out.
Last thing is the weak red. Rejuve is a last ditch cure. Get it running
right first. Testers are not perfect. I have seen nearly dead guns look
good & strong ones bad.
73 Zeno
LFOD !