[Hallicrafters] SX 101A hum: how much is too much?

[Andy Bullington]

After getting my SX 101A all back together and installed on my operating
bench, I got a mono adapter for my headphones and noticed ....hum!! At all
or no volume level, all or no rf level...doesn't seem to make a difference.
I never noticed it through the speaker but after discovering it in the
phones, I put my ear right in the speaker and there it was. Now I've
replaced all the filter caps and all the tubular caps. The only thing I
haven't changed out are most of the tubes. The rectifier and voltage
regulator are coppertops. Any ideas where to look? I'm waiting on a shipment
of NOS tubes but something tells me thats not the problem. Or is this just a
fact of life with old tube receivers? Thanks.
                     Andy W1AWB