Identify gizmo?

[Harley L. Miller]

I got a boatanchors gizmo at a hamfest recently and can't identify it.
Maybe someone on the list can help. A dymo label on the side says 'QST
Mar 1948', I assume its from that magazine. The major parts are:
6SA7
6SN7
6AX5
Large relay
1 pot
1 4pos switch
2 phone jacks marked "A" & "M"
1 6' cord woth a phone plug.
Anyone have a Mar 1948 QST or know what it is?

Harley L. Miller  WB0ROQ
hmiller at sound.net