I've been blessed by Royalty... ZENITH Royalty

[Tom_Ryan]

From my HB-3 reference library for the 24DP4A, the 'A' suffix following the tube type designation means the phosphor screen is aluminized. An ion trap magnet is required on this tube. Although aluminized screens are ion burn resistant, manufactures continued to use offset gun design in production for this tube.

The ion trap magnet is located in optimum position such that the trailing edge of the pole pieces located over the gap between grid No. 1 and grid No. 2 and rotated for maximum brightness. Typically, a Heppner No. E437 or JEDEC No. 117 or equivalent is used.

In other words, don't be afraid to grab onto the ION trap magnet and and move it around; chances are it will need a bit of tweaking. Following the above procedure just leave it where the brightness of the picture looks brightest over all.

In addition to adjusting the ION trap for brightest picture, also check the ultor voltage. The center design value for these tubes in operation is 18,000 volts. The maximum do not exceed value is 20,000 volts. You may need to play with width and horizontal drive to get the best combination that gives an optimally bright picture. I would first start with a fresh set of tubes in the video and horizontal stages before proceeding with any adjustments. There's nothing like having good emission before tweaking.