[Arran]

That 1 meg in the eye tube socket almost always needs replacement if you want the eye tube to work correctly. Zenith should have put the resistor in the chassis, or at least made the socket less breakable.

It looks like the 1938 brand Z models used the infamous Eby magic eye sockets, so their role in this had little to do with designing the socket so much as selecting and acquiring a poor product. Those sockets are weird, rather then using a normal six pin socket and putting a cover on the back, the main body of the socket is a cap with cavities for each tube pin, the wire is threaded into each hole, the contact soldered onto each wire, and then a phenolic wafer snapped into the front to hold the mess together. The reason I know about these is that Canadian RCA and G.E sets from the early 40s used to use them, like a JK-70 or an A-22, which stupidly have the rectifier tube mounted right next to the magic eye cable roasting the wires to death. The 1 meg resistor can be dealt with without opening the sock, but a flaking cable cannot.
Regards
Arran