It was the cable going to and from the reverb tank. After swapping tubes and having the hum problem, I began tapping and found that tapping and moving the reverb tank resulted in the hum/no hum. I found the 4 tab connector loose. I went to Radio Shack and bought a better connector.
So, when you get the reverb tank you can check that as well. My tank sounds even better now than it did before.
You found your issue but this is a common issue for another reason .... A lot of folks think this is tubes since it comes and goes but in most cases it is the ground on your wall and noise comes and goes on the common ground.
Try a ground lift .... one of those two prong adaptors on the reverb unit .... I bet you find the problem goes away.