/vr/ - Retro Games

I have one crt that exhibits a problem but I'm no techfag so I'll ask here.

Pic related. Right part of the image is how things tend to look on it although obviously much less exaggerated (image was made in gimp). A kind of "ripple" or instability is noticeable primarily on vertical lines and high contrast text in particular.

Is this a tube problem, or something on the board? I hope its caps, but I have seen plenty of old CRT's with old caps and none of them do that. The tube in particular looks reasonably good when it heats up but it takes a minute to reach full brightness so it is quite old and abused.