Odd focus problem in 1938 British set

[dtvmcdonald]

Is there an ion trap and/or some beam alignment components on the neck?

Not at the moment. It never has had an ion trap, its a straight gun. However,
it has what they call a "push-about coil" which is like an electrically driven ion trap like thing and sits just below the yoke (the CRT is vertical). Its for centering That gizmo's correct setting was "off" so I physically removed it to no effect.

Are the effects sensitive to yoke rotation? If so, can it be improved by rotating the yoke and then rotating the whole CRT and yoke together to get correct picture orientation?

I don't know and am very hesitant to try ... the yoke is clamped on and the screw is stuck due to rust. The push-about coil was too, but much much less so and one drop of PB blaster freed it instantly. The deflection yoke has an iron core which comes off in pieces ... it can't slide off since the tube plug
is a monster rectangular thing perpendicular to the neck.

Is your degauss coil strong enough?

NO

Can you get to all sides of the shield?

NO

A bulk tape eraser could be worth trying.

That was my next guess at a try. But I don't have a strong one ... my
old one got lost somehow over the decades and in any case it was too big.
I'm thinking of making another one from a power transformer. The old one was the transformer from a CTC-5 with a burned out B+ winding and the I-core laminations removed. It would bulk-erase 2" videotapes.