Dennydog,
Your Atwater Kent is absolutely beautiful.
I had a model 55C (1929) model which I gave to my brother who restored it. I am sure yours uses a type 80 rectifier tube.
For your reference you may wish to check out this website. I didn't see model 72 listed, but model 70 looks identical to yours. According to the website, your's was built in 1930.
http://www.atwaterkentradio.com/