Been down the workshop and got a bit further:
Tested PY82s PL81 and PY81 all good as new except a slight g-k leak on PL81
Checked resistors in line bistable, a few are out of tolerance and am going through them and checking results in between:
Changed R51 (bistable HT feed) C42, C43, C44 (cathode bias decouplers/feedback and flywheel damper). Turned back on and get improved bistable line waveform - now 130ish Vp-p (no real way of accurately measuring). Picture brigher and sharper.
Decided to do more investigation of CRT grid circuit: cleaned and resistance checked CRT socket - all ok.
Then spotted C35 - vision interference coupling cap - not spotted it before due to badly printed circuit! Snipped it out and brightness control works as advertised!
Schoolboy error - I really do deserve kicking up the workshop if Trevor's got his boots on!
Fed in Aurora via attenuator and could get something like a test card after a bit of fiddling with line controls - even looks as if the APC is sort of working!
Not sure what I'll tackle next probaby more line-drive resistors...But am relieved that tube looks pretty good!
Dom