Zenith was a manufacturer of radio and TV sets. They rebranded tubes from a major supplier and offered them under their own brand in a similar way as Philco did. Zenith sourced their tubes mainly from Sylvania.
An early Zenith tube box:
In this case a box of a 26 triode :
The pins of the tube could be pushed out at the bottom to allow testing of the tube without opening the box:
A Loktal 7A4:
A Octal tube box in a different design:
The top and bottom of the box:
Later they changed the color scheme to yellow/black similar to the latest Sylvania boxes: