rca roundie

[mustang84]

vertical is working good.full picture with the right proportions.watching it today and the bottom 1/3 id lighter that the rest.slightly out of focus because of brightness issue.looks very good just this problem i wiggled tubes around in their sockets,no luck.tapped on the circuit board hoping to find a break.none found.rotated focus control and can get bottom very sharp but the rest goes soft.picture tube is a rca rebuild that was checked and is excellent.i really like the picture just this bothers me.i will try to swap out video and blanker tubes to see if it changes.after that i am at a loss