Just to add more suggestions: try disconnecting the clock motor and see if you still get the hum. Try flipping the ac plug at the socket. Is the on/off and volume the same switch? If so, deoxit again and check it. Check the leads and make sure there's no shorts or cat wiskers. If you have the Sams, check to see if it mentions any critical lead dressing. Check to see if the speaker housing is making contact with the chassis inside someway. Try blowing out everything with compressed air.

I've been there too. It really is a process of elimination and can be time consuming. Try taking out the filter caps and checking them on a meter, or swapping with others. I had a bad new cap once.