Bugger!
Got ahead of myself somewhat. Sub was checked on another system using line input. Didn't check speaker input, which is still not ok- faint even on full volume, though the hum is gone.
Will have to reflow pre-amp board- which was not done- for starters.
It is, however sounding well- better than before. New capacitors no doubt help- and probably the Clearline surge protector/line filter multiplug I bought.
Have to be very careful with the volume as it leaps not creeps. Also a bit of a pain cos I'm using Tape on my VA amp as it is the only input that has an output. That means unplugging and plugging cables whenever I change source from CD to AV.