[Phil Nelson]

Round "porthole" TVs look cooler when they're turned off than when they're actually playing. I think the porthole design was an impractical gimmick (or perhaps simply naïve design), and that's why the vast majority of B/W sets with round tubes used rectangular masks.

A TV image is by definition rectangular. If you expand it to fill a round screen vertically, then you lose a bunch of the picture in the corners. If you shrink it to fit the entire image on the screen, then the round tube looks dumb, with big blank areas for no apparent reason. Some B/W porthole sets even had a switch allowing you to flip from one screen mode to the other, suggesting that the manufacturer knew that neither of those compromises would satisfy everyone.

Anyhow, there's nothing to prevent you from making a porthole color roundie, if you want to throw away your mask and you can get enough vertical deflection from your set.

Phil Nelson