the Cathode from the rectifier valve (6X5G) connects straight to the top of the reservoir capacitor on the far left, and then through a resistance (hidden on the reverse of the board) to the top of the second large white capacitor for smoothing.
the smoothed HT is then fed only into the transformer thing via the yellow wire, while the other three wires are connected to either the anodes or grids or something of the valves. it doesn't help that i can't ind the pin outs for them, nor even what one of them is!
anyway, my first thought was a choke, but since theres 4 wires it seems more likely to be an interstage transformer or something. but then, how does V3 get its HT?
Finally, heres the valve which i can't identify. all its markings have rubbed off except a small part of an octogan with 6 and 5 in it like this
/
| 6
| 5
\
that isn't perfect but i hope you get the idea. inside the actual valve is written " 276B" or "27613" in handwriting. I think thats pretty neat, it must have been written at the time of manufacture, and hermetically sealed in a vacume forever.
actually, why haven't i thought of looking up that number incase its a valve number?
it has 6 pins, so that suggests a triode like the VR67, except that pins 8 and 1 are earthed in the circuit, and i dont see a potential for a negative grid bias. maybe its a directly heated cathode?