It turned out ,for same voltage out and for my ,in effect, manual
winding, the same length of wire required , going down from .32mm to
..28mm. Using just the Es minus 1, and no Is , magnetising not complete
and could only run the variac up to 70 per cent or so, but gave the
voltage ratio at 50Hz. Next time I'll probably add the Is as well, as
its easier inserting the Is than the Es. Tip for final E insertion,
force a razor blade in between the interim last E and the bobbin, then
insert the last E between the razor, bent a bit, and the in place E.