[MrFixr55]

Updated-

Hi Snowlion,

+1 on above comments. It was very common for radio manufacturers to put a non-standard jack on the rear apron of the chassis for power to the phono turntable. Sometimes it was 3 pin so the record changer's switch would power on / power off the receiver chassis. In this case, the power switch was not usually on the volume control off and was labeled Off/Phono or On.

However, chances are that this chassis was available as part of a tabletop radio / phono combo where the turntable was not a changer. Both legs of the "phono power socket" were switched; one by the Radio power switch, and the other by a "Radio - Phono" switch. not kosher by current NEC standards, but this was within the appliance.
Verify that on your set, the switch exists and can be switched to Phono. It may be hidden or its travel blocked, as this is an AM / SW Radio.

An easy fix to this would be to clip the socket from a set of Christmas Lights or find an old non-polarized extension cord and clip the outlet from it. Pass the wires through the holes and tack- solder them to the tabs of the pins of the apron socket that the supply wires are soldered to.