[Mondial]

Since it is already there and looks period to the radio, you might consider keeping the jack. A extra audio input really comes in handy if you ever want to connect a higher quality audio source like a CD player, etc.

Typically the jack just connects to the top of the volume control, with the switch selecting either the detector output or the external input.

You would be surprised how good the audio quality of these radios is when fed from a decent source rather than an AM station.