[Hallicrafters] 5-pin socket pin-out / The plot thickens

[Mike Everette]

Why not just check for continuity?  If you have it between two pins on these early tubes, those would obviously be the filament -- unless the tube has a catastrophic short.

I would be willing to bet a dinner at the Scottish Steak House (home of the McSteak) that the filaments of a 5 pin tube are 1 and 5 and the isolated pin is number 3... unless this is some sort of Bulgravian tube.

73

Mike
WA4DLF