I got what look like the same tubes as this a few weeks ago, RCA 12J5GT, in the box labeled as Bendix (but says RCA on the tube), and also from 1942. I've spent probably 2 weeks with them in the SN7 slot now (as a pair using an adapter) and I actually think I like them better than their metal 6J5 cousins. These are the only glass RCA J5 tubes I have, but I have too many metal version to count, including several that are right around the same years as the 12J5GT. They have the same characteristics as the metal 6J5 (nicely described by
@wenbinbin2010 ), I just think the 12J5GTs have a bit more of what I like about the metal 6J5s. Yes, they were more expensive, but I am ok with $20 for the pair.