[Tubesforme]

If I were working on this radio I would determine which path the hum is taking. Again assuming that both the tube and the socket are good there are only two likely paths . Either thru #19 cap or #20 resistor into the 27 tube.

The first thing I would do is to lift the #19 cap as that won't affect the bias of the 27 tube and will break the path from the IF detector. If the hum stops then we know it's from there. Hum still there then it's the bias line thru the #20 resistor.

If the hum is from the IF detector then as Steve mentioned the #14 cap and the #18 resistor should be checked.

You are very right on isolating where the hum is coming from. I know it is from something in the bias supply and the only part I am questioning is the interstage transformer (even though it is a new transformer) as all other paths have been eliminated. The bias resistor and the power divider resistor all are good.