A display device comprising a plurality of prize balls, a ball holder adapted to hold the balls in an individually controlled manner, a controller adapted to select a prize ball, a display mechanism adapted to display the selected prize ball to the player; and a positioning mechanism in communication with the controller adapted to position the selected prize ball relative to the display mechanism. Preferably two adjustable channel assemblies are mounted to a column wall to support a rear spacer wall that defines a back portion of the stack area. By changing the X, the LO output power is controlled and the back-off amount of a transmission amplifier is changed in accordance with an optimal modulation scheme.