99% of the time one end of the filament goes to ground.
If on a PCB GND usually tied to chassis by the board being
soldered in. If a kit may use nuts, bolts & star washers or
jumper wires to main chassis. Cold joints very possible either
place & the socket pins.
If hand wired it may use twisted pair. Most the time brown or green
wires used for filament.
If miswired just follow the hot end from a near by tube, put in a
clip lead to get the 6.3VAC to the 6FG7. Use meter to be sure you are
jumping the right voltage !
There were a few sets with most filaments in series & a few
in parallel, Maggy IIRC. If so watch for fuse or fusable links.
73 Zeno
