HW-16 hums on receive...
Of course the power supply electrolytics are the first thing to check - in fact check all the electrolytics in the set. But you're probably way beyond that by now.
Then try these tests:
1) Turn set off, pull the 6GE5 final tube. Does hum go away? If so, you have heater-to-cathode leakage in the 6GE5 and the cure is a new tube. (Found that one the hard way - all the received signals had hum on them, even though everything checked out perfect. The HW-16 TR system involves the 6GE5 cathode, and any AC on it modulates the incoming signals)
2) Turn down AF gain - does hum go away? If so, it's getting into the set before the AF gain control
3) Turn down RF gain (with AF gain up) - does hum go away? If so, it's getting in somewhere in the RF or IF section. Try removing tubes one at a time to see what kills the hum.
73 de Jim, N2EY
btw, the 6GE5 is just a compactron 6DQ6. A reversible socket swap permits using a 'DQ6 if you can't find a 6GE5.