Are you sure you followed the above ?You need to follow the procedures outlined from page 111 to 123 in the linked pdf below.
If you don't have a plastic hex driver for the width adjustment, DO NOT FORCE IT and DON'T use a metal tool - you will break the component (and they are impossible to buy new).
ALWAYS be careful not to bump the circuit board on the rear of the tube. The SE & SE30 vacuum seal teat is very easy to break.
NoSo the lines OR background you see on the screen DON'T change in brightness when you adjust the Cut-Off (Labelled below as 'Brightness Control')?
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It could - but a rare case if it is. High tension seems to be working - the raster looks good.Couldn't it be the flyback?