[Raleigh]

It was fairly common for people to add phono inputs to radios of this vintage. That way they could buy a turntable without an amplifier and speaker, and play records through the radio.

Usually the owner or a repair man would add the phono connection (an RCA jack like you have) between the 2nd detector diode section of the 1st audio tube and the amplifier section of the same tube so they could take advantage of the volume and tone controls. A switch was usually added to disconnect or ground out the radio signal so sound from the radio wouldn't bleed into the phono signal.

There were different ways to connect the phono input and disconnect switch. You might want to make a careful diagram of where these wires go so you can reconnect them when you finish the restoration, sine they won't be in the schematic. You can connect various modern music players like iPods and so forth to them if you want. Or you can remove the modification, since it wasn't original.

I have an excellent book that was a textbook for radio repair students. It's "Elements of Radio Servicing" by Marcus and Levy. You can download it from the alternate radio forum here. http://antiqueradios.com/archive.shtml It's in six pdf downloads that you can read on your computer or print out. Used copies are also available for $26.79 and up from Amazon's partner booksellers. In my copy, (1947), there is a section on how to wire-in phono inputs for radios that didn't come with them. Chapter 12, page 179.