A question of polarity

[Paula]

Here's one for the experts...

I'm replacing the electrolytics in a Silvertone 7251, and I am not sure about the polarity (they show up as E1 and E2 on the schematic below.) They were originally part of a 2-section cardboard unit beneath the chassis, with three wires coming out - black, green, and red.

My first guess would be that the black wire is the common negative for both caps, but I have seen exceptions to this. Does anyone know for sure?

Paula