I see that these have some insulation around the lead wires. This was apparently to mitigate or completely solve the problem of glowing
lead wires on the Burroughs models of these tubes. I have a clock I built in 2010 that uses (6) NL-6844A tubes mounted on the front of
the enclosure with the sockets mounted flush so the tubes protrude out in the open. 6844A is a notoriously lousy tube because it has no mercury and therefore
it ages very fast. But in my humble opinion, 6844A makes up for it by looking great for at least a little while. That being said, I have rounded up a bunch of spares
including 5031 types, 5037, 5092. Plenty of spares. But what I find time and time again is that the Burroughs 6844 tubes hardly ever work. They very often just light up the lead wires only.
I have therefore given up on the Burroughs tubes of this style. National NL-6844A hardly ever disappoints. Most of those work real good. And of course 5092 is much much better due to having
some mercury.