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It is my understanding that both the first b&w CRTs and the first color CRTs were round due to pincushion issues. That is, the rectangular picture would have a pincushion(the tops and sides would bow inward)effect unless correction was added. For b&w sets, a permanent magnet scheme was developed. As this would not work for the 3 beam color tubes, it took some time to develop the circuitry. Developing the square CRTs is another issue.
For a round tube b&w set, any late 1940s TV is a good example-almost all have round tubes.
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