Bruce ,,I am certqinly no expert in this area ,but it sure sounds like you need to replace the electrolytic caps. in this unit.. That is most likley the cause of the hum,,more likley than a bad tube.If the caps are bad it could damage the power supply.
Next I would check all the connections and make sure they are making contact.. It might be a cold solder joint.. That is where the solder is in place but it has not made good contact.. Also ,,the switch that controls RADIO/PHONE should be cleaned as it may not be making contact.
Because you did get sound at one time makes me think that there is a loose connection
I find that as a beginner,I go over everything to see if all the wirese are making connected.. You can purchase capasitors at” Just Radios”’.I do hope this helps Dan in Calgary