RCA C73275 Developmental One Gun Color Tube
This developmental CRT was discovered by Chuck Azzalina, in pieces. He spent many hours putting together what he calls the "three dimensional jigsaw puzzle." The tube uses a shadow mask, with a single electron gun. An electromagnet around the neck of the tube deflects the beam to the proper color dot. Here is awhich describes this approach. RCA probably gave up on this approach because of the difficulty in getting proper convergence, and the low light output compared with a 3 gun tube.
Chuck has generously donated the tube to the Early Television Museum, where it is on display.
A RCA press release, probably about this tube