TG&Y Contrast don't stay put

[lnx64]

This may be just because it's a cheap as hell chasis, but I made this video a little while ago on this TG&Y (Sampo) TV, and you'll notice in the video game as I race, the contrast just keeps going all over the place..

http://www.youtube.com/watch?v=PY60CpSXlog

I tried the CRT in my friends IBM 5151 computer monitor (same CRT actually, was surprised), with the yoke from that monitor, and the CRT worked fine, no contrast issues whatsoever, nice and stable.

[Eric H]

The set probably has no, or very poor DC restoration so it can't hold a consistent black level.