I'm done with the alignment and now on to some details.
I noticed this from the beginning. There some white horizontal lines that "flash" every so often. They are usually near the top of the screen. This happened before I did the retrace blanking mod. They increase in brightness with the "Brightness" knob. If the picture is just a little too dark, they almost disappear.
I've cleaned all the tube sockets and their pins.
Any ideas. Thanks.
https://youtu.be/cFoYIfubVkY