This photo of the KAAY tower base shows the Austin transformer. The Austin transformer is a toroidal transformer that is used to transfer tower lighting AC current to the tower's obstruction lights. Since there can be no electrical connection between "earth-bound" circuits, and the tower itself, the Austin transformer is the only way to get AC current onto the tower without making a physical connection.

The arc gap balls are used to suppress static electricity charges and lightning by creating an easy path to earth ground. Just the simple blowing of a summer breeze can generate an incredible static electricity charge on the tower, and occasionally, even on a breezy sunny day, you might be able to hear the "crack" of a spark jumping across the arc gap to ground.

From: http://mighty1090kaay.blogspot.com/2011/07/glaspie-et-al-by-dave-m.html