[ChrisW6ATV]

I started my electronics career repairing arcade video monitors in 1981. I could get the convergence darn-near perfect on most of them, and I replaced a lot or CRTs when they arrived damaged (we were a factory service shop for several game manufacturers). These were all 19-inch CRTs, which were standard in the Berzerk/Defender era. (Maybe larger CRTs are not as well converged in general; I have not worked on those.) Yes, these were inline-gun CRTs, with modified JVC chassis and 15 kHz input. Static/center convergence was set with the rings on the neck (after doing purity and positioning the yoke), then center-of-edge convergence was done with judicious tilting of the yoke's front diameter, which was not up against the CRT even though the back of the yoke was already tightened to the neck with its band. With the proper position, the yoke was held in place with three rubber wedges about 120 degrees apart on the cone of the CRT. Lastly, corner convergence and some edge fine-tuning was done as needed with the small magnets on the cardboard strips. The strip has a thin small magnet on one end and some adhesive tape on the other end; the whole thing is about 2.5-3 inches long. You slide the magnet between the yoke and the CRT bell and watch the raster with a crosshatch pattern and move it until the error was gone, or reduced. A good one needed only three strips (one in each of three corners); some of the worst needed up to ten strips to get them into really good convergence.

I used similar strips when I have replaced Sony Trinitron CRTs on 25-27" monitors in more recent years.