Scope question

[Tube Radio]

I have a question about a DuMont 304H scope that has a 5ADP1 CRT installed in it.

Up until about 5 years ago the scope (mostly restored) worked great and the CRT always focused properly.

One day while using the scope to watch TV (required two pother scopes to do that) the picture got out of focus.

When displaying a trace the focus control now has to be nearly full CCW for proper focus, but when displaying a waveform the focus control has to be at least 3/4 CW to somewhat resemble proper focus (never focuses as sharp as it does when just displaying a trace) which I know is not right.

I've tried another 5ADP1, a 5ADP2 and two 5ADP5 CRTs and all have the same problem. I even got another 304H scope with a 5CP1A CRT installed and tried the 5ADP* CRTs in it with the same problem while the 5CP1A CRT works properly in my original 304H.

On another forum I have had at least two topics over the years and have one going now without any answer as to why I have this problem.

I cannot use a 5CP1 CRT as I did use this scope at times to measure waveforms.