Some tubes used in games are monitor grade tubes: M48AA... 19VLU...
Convergence issues in these monitors come from a few different issues:
-poor installation of replacement tubes (many of the wrong type) and servicing by their techs.
-warped yokes and convergence/purity magnets from the years (and years and years) of use and heat inside the cabinets.
-manufacturers choosing to cut corners in their monitors to maximize profits.
-CRT's improved over the years such that we expect better performance.
Remember that these games were designed to get as much $ for their owners in a short period and were never designed to last as long as some of them have.
I opened a NIB game a couple of years ago, and the setup on the monitor wasn't that bad considering that the game was shipped over 25 years earlier, and the setup was done in a factory 1/2 way across the globe without knowing where they were going to be used.
Some monitors need to have more than a few stick on magnetic strips to dial the convergence in spot on:
http://www.youtube.com/watch?v=QYB1L...eature=related