[DaveWM]

weak picture poor lock, AGC issue.
as far as the shrink in picture
Have you checked the B+ at turn on and then again as it shrinks. Monitor the B+ and the AC current draw, something like a gassy tube may be drawing more power as it warms up.
How is the HV holding up?
Have you tried new horz out/damper/HV rectifier (SOP if HV or sweep is an issue, must sub don't use a tube tester).

I assume the shrink is there when just a raster as well?
If you are going to do TV work a few must have items
HV prob
neon light for checking fly
Nice thing to have and can be gotten cheap
B&K 1076 analyst good for trouble shooting HV and for signal injection to trouble shoot RF/IF/video issues
Scope for checking wave forms and looking for things like hash on AGC and sync separation issues.
AGC variable DC supply for trouble shooting AGC issues (included on the Bk 1076).