Here's what I can find on Zetka CRT's: their 15 inch flat face tube was a 15CP4, but was similar to Dumont's 15AP4 with an ion trap.

Zetka did supply other makers, but I can't find out who specifically. They were the first to make an all glass 16 inch tube, the 16DP4, where before there was only the metal cone version.

Zetka started around 1927 as a radio tube maker. In 1946 they were bought by U S Television Corp. but apparently remained a separate company. A guy named Hamilton Hogue was president of both companies. In 1950 they bought the patents for a color tv tube from a company called Sightmaster Corporation. Apparently nothing became of that and they soon disappeared along with UST.

I did find a report that UST started selling TV sets through Macy's in 1946.

Correction