First rectangular set / CRT

[dano]

Looking through photos of old sets, I've been noticing that round and "double D" masks seemed to fall out of favor around '51 or '52 or so and the more typical rectangular mask of the later 50s started to be the norm. I started to wonder as I looked through old pictures, do these sets have a round tube behind the mask, or are they rectangular CRTs? I have a Hoffman (beyond repair) that looks like your typical rectangular set from the front, but inside has a large 19" round CRT... a good percentage of which is covered up from view. When did rectangular tubes start to show up in '50s TV sets? Did they phase out round CRTs (in consoles and larger sets) rather quickly?