screen issue

[radio nut]

My next project is a CBS-Colombia tv. As of now it is up and running. I have noticed that the left half of the screen is a little brighter than the right. The horiz. hold moves that left side brightness around though. All caps are new, all not really close resistors are replaced, and the tubes are nos. The only thing I have not checked is for gassy tubes(My main tube tester broke and my other does not check for gas).I currently do not have spare tubes for this set to sub in.What would likely be the cause of this condition?