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Quite often, hum can be caused by electrolytic filter capacitors that are no longer filtering. In table radios, they're typically a cardboard "can" under the chassis attached with wires, with two capacitors in one can. You can replace these with regular modern electrolytics. Electrolytics deteriorate with age, as well as heat. Leaving the set on all night may have been enough to push aging caps over the edge. If you're going to replace the electrolytics, do all the paper capacitors while you're in there. The radio will thank you.
Another thing to check, if you have spare parts or another working radio - is swap tubes around. Although not likely, I've heard stories of hum caused by a failing output tube (50c5).
-Ian
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