I just made up some working test setup for the homebrew oscilloscope project and the screen came to life for the first time:
By the way is the 3KP1 / DG 7-113 with the green p1 phosphor. If you ever come across the white phosphor (3kp4) you found some nice piece of rareness. The P4 version was used in the Pilot TV-37, one of the first portable TV-sets. Check out David and Marlene McClellans blog about restoring one! Also check out some video of it here.