Having trouble deciphering an amplifier layout. Help?

Here is the pdf of the layout. And another. And a schematic (which i can't read).

the only thing i'm having trouble with is the thing next to the transformer. in the colorful pdf layout it's just a grey circle that the red blue and yellow wires go into. In the b&w layout it's just a circle with three little black dots to tell you where the wires go. I can't find it in the schematic.

This is for a 1964-67 Fender Vibro champ guitar amplifier. the amp only has four tubes, which are along the bottom in the layouts, so it's not a tube.

Thanks.

edit: is this possibly a can capacitor? if so why are the values not labeled?