[Mondial]

You need to have all wires of the speaker connected for the radio to operate. The field coil of the speaker also acts as a power supply choke to filter the DC output voltage. To do any testing of the radio outside of the cabinet, you need to remove the speaker also and connect it to the chassis.

Looking at the photo of the underside of the chassis, I see only one replacement electrolytic. Did you also replace the other two? If not, this might be the cause of your hum?