A continuous tape cartridge used by radio stations for jingles and other short, repeated content. Mackenzie Repeaters were also used to synchronize sound effects for amusement park rides and to provide music for movie soundtracks. The specially lubricated tape could be recorded on a standard tape recorder, cut to length, loaded into the cartridge and spliced to make an endless loop. A short piece of foil tape was applied at the appropriate location to end playback. The cartridges could be loaded into machines that held five or ten tapes at a time, allowing quick transitions.

AM radio underwent a transformation from the late 1950s through the mid-1960s as television began to grab people's attention and advertising dollars. Transistor radios, introduced in 1954, brought radio out of the house and into active life. The Top-40 format, introduced in the early 1950s, emphasized repeated playing of a short list of songs. In 1960 radio station KHJ-Los Angeles adopted the new format. According to A. J. La Franco, KHJ program director:

Our programming, now made up of much smaller segments than before, had to appeal and hold our listeners. It had to be tight, bright and fast. …we owe a great deal to the program repeaters manufactured by MacKenzie Electronics (MacKenzie Electronics Ad 1960, 121).

MacKenzie carts were also used for background music on movie soundtracks, for which the company received a special technical Academy Award in 1962. Disneyland adopted MacKenzie carts and players in 1955 for its Audio-Mation system, which used hundreds of MacKenzie repeaters to provide synchronized audio for the Haunted Mansion and other park rides (Irwin 2004). A MacKenzie system was still in use in 1978 at Palace Amusements in Asbury Park, New Jersey for all audio in the arcade (Senna 2024).