[morzh]

It does not look as if your speaker(s) have a humbucker; if they do, the field coil orientation does not affect hum, but the humbucker relative to the voice coil does.

Check the 53 cap (the AC line filter) for the ground lug being grounded (check from actual lug, not from the screw).
Check electrolytic caps for proper capacitance, filter choke, the cap across it - you might even try to disconnect this cap and increase the electrolytic after the choke.....