6SN7 tubes "made in USA" branded Sentinel. ????

Since this is a preamp tube, I posted here. My question is who might have made these tubes? RCA?, GE?, ???
Sentinel was a brand of tube radio. They may have had special branded tubes made by someone else. Or maybe they made their own ??

These were all popular styles back then. These look like radios made by PHILCO and CROSLEY. Sentinel had their own tube line, as I remember. Black & Red or Dark Brown & Red box. I have to check my Dad's store, he still has these radios around.