Opinions on what's wrong? (Video attached)

[Nick_the_'Nole]

Now, the 50C5 does have a tendency to develop H-K leaks/shorts... have you tried a different tube?

I had a similar issue, actually in a similar GE radio, come to think of it, and it took me awhile to track it down because the tube tested perfectly fine. I had a 120 cycle hum, yours is more like 240, but then again you also have an AC motor in the mix (the clock), which could be putting spikes out on the line.