[Boatanchors] What they for?

[TELEGRAPHER at att.net]

All i see on the top of them where they is a connector like for a Microphone although i don't think that's what it really is all about.  Anyway i have 4 of these and the label on the top says: Sensitivity Test Plug Type P3000.  They are 4 pin and have the shape of a tube.  Probably for a tube tester although i don't know which one.  Two of them fit into a nice wooden box and all 4 have the same id tags.

Any ideas?  A 5th item has two pins on the top like an *833 tube would look like but there is no tag on it

Larry
W0OGH

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