[mountain man]

what is this? phono plugs into it. model 42-1003 not bol equipt.

[Radioroslyn]

It's the audio input transformer.
Terry

[Chuck Schwark]

Most likely for a crystal type pickup to match into the audio section of the radio.
Probably modified by user or a radio shop. (?)

Note:
The 42-1003 originally had a Beam-of-Light pickup arm, as shown in The Gallery.
To be sure you have a 42-1003 set, it should have two bands AM and SW.

The 42-1001 and 42-1002 were AM only and originally used crystal pickup tonearms.

Chuck