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 a paper which 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. Here is a photo of a set with this tube in operation.
huck has generously donated the tube to the Early Television Museum, where it will be on display for the 2008 Early Television Convention.
A RCA press release, probably about this tube