On Saturday investigating the state of some old CRTs (kinescopes) I have. A 10BP4 RCA made in the 13th week of 1949 had absolutely zero emission. Upon investigating the tube gun, I made this discovery. Follow the cathode connection and you will see a 1/16" gap!
I suspect it started as a bad weld and the tube tester in trying to restore the connection blew it wide open.
This is the second RCA 10BP4 in 50 years I have seen the same problem: last one in 1972! But I have only dealt with less than a dozen 10BP4s in that time.
