Video Problem need help

[ohohyodafarted]

I have noticed a video problem in the restoration of the Hallicrafter 820 I just completed

I do not know the technical name for this phenomonea so I will just have to describe it.

There is a horizontal band in the picture. It is about 1.5 to 2 inches tall and stretches across the entire width of the screen. The band is slightly darker than the rest of the picture. It causes a slight horizontal shift of the picture to the right. The band starts a the bottom of the screen and slowly drifts up the screen. When it reaches the top of the screen another band starts at the bottom just before the upper band disappears off the top of the screen. It takes approximately 6 seconds for the band to drift from the bottom to the top of the screen.

If you look at the photo of the Outer Limits still on the picture below, you can see the band across the forhead of the alien on the screen.

Does anyone know what this problem is called and what causes it? And even better how do you get rid of this anoying drifting band?

Thanks in advance for your help. I really enjoy being part of this group. I am learning a lot by reading posts here.