Need schematic, and/or suggestions of how to get rid of 60 cycle hum

My 40 year-old tube type NuTone 2015-016 intercom and am/fm radio developed a hum then eventually stopped working. I replaced two tubes, a 35C5 and a 19T8, which restored the radio functions. I still have the background hum and suspect it may either be leakage in some other tubes, or capacitors that died of old age. I need a schematic and suggestions of which capacitors or other tubes to replace. Or, where can I send the unit for repair. I live in a Northern suburb of Chicago. Replacing the system is an option, but for simplicity I'd prefer to first try to fix the unit and put it back in the wall.

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