The small building at the foot of each tower is called a "doghouse".
The doghouse at the base of the center tower contained the antenna tuning circuit for the center tower (daytime operation). It tuned the transmitter and feedline to electrically match the center tower for maximum transfer of the radio signal into the tower - the entire tower is used as an antenna.
The center doghouse also contained a separate set of tuning apparatus, used to divide the power three ways for the nighttime operation. Power from the transmitter was divided into three separate, almost identical signals, and then fed into the east tower, the center tower, and the west tower.
The nighttime radiation pattern (an hourglass shape) was created by a combination of the amount of power fed into each tower, and the physical distance between the towers, about 500 feet. In some directions, the signals from the three towers would "add" together in free air and create a much stronger signal. In other directions, the signals from the three towers would add together in such a way as to cancel each other out. The result was a very strong signal to the northwest and southeast and almost no signal at all to the northeast and southwest. Looking at a map, the KAAY radiation pattern resembled an elongated figure "8", tilted slightly to the left.
(For some reason, the network would not allow me to download the coverage maps we'd posted before, so here's the link to them: