[NostalgiaRadioTime]

Unless you can read the printing on the outside of the can on top of the chassis as to which color dot corresponds to which capacitor value, the only way to determine which is which is to trace the wires out using the schematic. It appears the common or "negative" of all three (#67 on the parts list) are tied together going to the center tap of the transformer, and that the 10 mfd is a positive ground. Meaning the positive side of that cap is going to chassis ground.