[morzh]

Well, now that you know where the MAIN goes, let's look at the 25Z5.

http://www.radiomuseum.org/tubes/tube_25z5.html
(this is the 25Z5 data)

1. The pins 3 and 4 of this tube (Cathodes) are likely connected together (or it can be just pin 4 alone) and then they will go to the first electrolytic cap's positive (the negative which is the common for both caps inside the single body as we established probably goes to the Chassis).
Find that cap's wire that goes to the pin 4 (or 3&4) of the 25Z5.
We will consider this the first cap and it needs to be about 40uF 150V (could be 200V or more, but 150V is sufficient).
Again, its positive goes to this point and the negative - to the Chassis.

2. From that point the following is likely to happen: this first cap's positive and 25Z5 Cathodes will have another wire coming to them and it will likely go to either:
a)some choke (the filter choke, something that looks like a transformer) or
b)The field coil of your speaker that doubles up as the filter choke.

The second wire of that same choke or the field coil will likely goo to the second cap (which can be the other wire in your electrolytic cap).
Trace it, mark it.
That capacitor has to be about 20uF 150V.
Again, this wire is its positive and the negative will go to the Chassis.
We will call it the second cap.

Let's stop here for now.