The tuning knob is the large black knob with the red mark at the 12:00
position. The knob doesn't turn all the way around, though. It just
moves from 12:00 to 10:00 to go down and 12:00 to 2:00 to go up.
Here's a link to a picture of the radio:
http://tinyurl.com/y8v9vw