Atwater Kent Model 30 Question

[polyphase]

A choke is not required. 500uf is way more than enough for the B+ supply of this radio. Please check the filters on the 67v and 22v supplies. Each should have a cap to ground, maybe 50uf, probably less. The detector supply (22v) is particularly sensitive to supply ripple.
A good earth ground, with the caps mentioned above and the C+ supply connected to it, hum will disappear.

footnote: One of my '20s radios had hum just because the line powered B supply was too close to the radio.