Pin #1 on a 5U4 Question

[Chris K]

Working on this Dumont "Doghouse". Someone replaced a socket for one of the 5U4 rectifiers and did a hell of a botched job rewiring the pins. As I try to untangle the mess, my first question is they used socket pin one as a tie point for two leads from another part of the circuit, essentially as a terminal strip tab. Pin #1 is internally connected in the tube but I don't think it does anything. I've read some threads where it was suggested it's a ground for the metal shell or it's there to physically stabilize the tube in the socket etc....
I'm asking because I'm trying to run down a short when the relay engages. If I leave the rectifiers out of the circuit, the relay closes and everything looks stable. If I wire either of the 2 rectifiers individually in the circuit or together as they're supposed to be, the circuit shorts and the relay goes into a loop of sparking, disengaging, sparking etc. Just trying to eliminate possible issues one by one, could there be an issue using this pin, #1, as a neutral terminal connection point? I would expect the previous tinkerer to have used a tab for pins 3, 5 or 7 as a tie point. So does anyone know why pin 1 is there on a 5U4 and can it be benignly used as a tie point?