[Heathkit] HO 10 Problem No Solution

[OTAKEBI at aol.com]

I have obtained a copy of HO-10 documentation.
I can see that best focus of CRT should take place at midscale of the focus 
adjustment.
Mine is getting best focus at full clockwise.
I have replaced the 330k and 3.3meg. resistors and the pot itself seems to be 
working fine.
Those are the only resistors I can see in the circuit prior to the blue wire 
that goes to the CRT off the pot.
Line is in focus when first on but as unit warm up it starts to get out of 
focus.
I think this could be normal warm up but since the best focus on the focus 
pot is not near center I can't refocus the line.
Now I think I found tube 1V2 to check on border line of my tube tester and I 
will have to pick out a new one next week at Orlando Hamfest but I don't think 
that tube has anything to do with the problem I am having.
Can anyone tell me if it does interact with the focus control.
Could the problem be the CRT itself?
I don't think so myself because the display stays bright.
Thanks for any input.
Dan/N4VET