even with the labels, there's some oddness. It looks like the fuses are in the common side of the circuit - except the 17V.

How the transformer is physically constructed/wired is different from bally...they tied the transformer commons together, where united kept them separated.

it also makes a little more sense if the rest of the transformer is in the picture, so below shows everything with some over-annotation.

united (resized).png

the 17V hot is wire 90. The 6V and 50V hots are both wire 30.

the picture doesn't show one piece of the physical reality ... extend the 4 black bars that represent the stator (transformer metal the wires are wrapped around) up so they reach past the 17V winding. Then the 120V primary at least looks like it's independently inducing current in the 17V winding....i.e. the 50V fuse is not really in the 17V circuit path.

Although the current flow is really back and forth, you can imagine it like a clockwise flow in the 17V and 6V circuits, and a counter-clockwise flow in the 50V circuit. i.e.:
17V: wire 90 to wire 80
50V: wire 30 to wire 80
6V: wire 30 to wire 50

why the transformer has two commons I don't know. I assume it has something to do with circuit isolation, efficiency or load handling/wire sizing, but I kinda skipped that class in school.

why the 17V fuse is on the hot side and the others are in the common....I guess if the fuse was also in the common, and you shorted the hot 17V to the hot 50V/6V, there'd be no fuse in the path.