[matspar]

I'm thinking exactly that John. The line and frame oscillators are both ECH35's also, so I shall try replacing both with new items to see if this corrects the line non-linearity. Both chassis although having required extensive cleaning are in remarkably good condition. The 663A has never been anywhere damp in its life by the look of it.
I've fitted a 31-74 as the 31-16 (itself a replacement from the original 31-7) was completely flat. I suspect this set had quite a life back in its day.