Substitute 12KP4 for a 12LP4

[Eric H]

Originally Posted by Eric H

It should work fine, the 12Kp4 is shorter and aluminum so it shouldn't need a trap.

The focus coil could be pulling the beam off center if it's too far out of adjustment but I would suspect the lack of Dag in this case, I had a set that wouldn't operate with an uncoated tube.

You could try an Ion trap, the tube may have been rebuilt at some time with a gun that requires one, if the neck is too short you might have a problem installing it though.