Heck of a lot to respond to there....
Quick hum diagnosis tip. If you can disconnect the B+ with a lytic still in circuit giving a couple secs B+, but keep the heaters going on AC if the hum persists when the B+ is disconnected from AC that indicates heater/line cord hum leakage (or perhaps field coil issues if it does not use a PM speaker).
If hum seems to be in the heater circuit try unplugging the set and see if it hums for the second or two it runs with the plug pulled.
Standby usually cuts off B+ while leaving heaters on. If audio/hum persists in standby then there is something wrong with the standby mode.
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