The Fidelipac, commonly known as an NAB cartridge or simply cart, is a magnetic tape sound recording format, used for radio broadcasting for playback of material over the air such as radio commercials, jingles, station identifications, and music. Fidelipac is the official name of this industry standard audio tape cartridge. It was developed in 1954 by inventor George Eash (although the invention of the Fidelipac cartridge has also been credited to Vern Nolte of the Automatic Tape Company), and commercially introduced in 1959 by Collins Radio at the 1959 NAB Convention. The cartridge was widely used at radio stations until the late 1990s, when such formats as MiniDisc and computerized broadcast automation made the Fidelipac cartridge obsolete.
The Fidelipac cartridge was the first audio tape cartridge available commercially, based on the endless-loop tape cartridge design developed by Bernard Cousino in 1952, while Eash shared space in Cousino's electronics shop in the early 1950s.
Tape format 
Fidelipac was originally a 1⁄4-inch-wide (6.4 mm) analog recording tape, two-track format. One of the tracks was used for monaural program audio, and the other being used for a cue track to control the player, where either a primary cue tone was recorded to automatically stop the cart, a secondary tone was recorded to automatically re-cue the cart to the beginning of the cart's program material (in some models, two secondary tones, one after the program material, and one before it, were recorded to have the cart machine automatically fast-forward through any leftover blank tape at the end of a cart's program), or a tertiary tone, which was used by some players to trigger another cart player or another form of external equipment. Later versions used three tracks, two for stereo audio, and the third for the cue track.
The standard tape speed for Fidelipac carts used in the radio broadcasting industry was 7.5 ips, although some cart players and recorders could be set to record at other speeds, such as 3.75 or 15 ips.
Cartridge format 
Unlike the later consumer-marketed 8-track cartridge developed later in 1964 by Bill Lear which had the pinch roller integrated in the cartridge, the Fidelipac cartridge had a hole in the right-hand bottom front corner of the cartridge, where the pinch roller, built-in to the player instead, would swing up into place to support the tape up against the capstan. While Collins and Gates/Harris machines had the pinch roller automatically swing up into place when the playback button was pressed, with Fidelipac and ATC (Automatic Tape Cartridge) machines, the operator had to physically push or pull a lever to get the pinch roller in place before playback could begin.
There were three sizes of Fidelipac carts available — the 4-inch-wide A size (Fidelipac Model 300, 350 and MasterCart), which was a standard 8-track size cart with maximum 10 1⁄2 minute playing time at 7.5 ips; the 6-inch-wide B size (Fidelipac Model 600), a larger cartridge designed for holding longer programs; and the even larger 8-inch-wide C size (Fidelipac Model 1200), often used for background music applications.
The A size Fidelipac cartridge was later adapted by Earl "Madman" Muntz in 1962 for his Stereo-Pak cartridge system, which differed in two ways — the number of tracks used (four in this case, with two played back at a time to provide a total of two programs of stereo audio), and the tape speed (3.75 ips as opposed to Fidelipac's standard 7.5 ips). Unlike the Fidelipac players which used a stationary head, the Stereo-Pak system used a moving head to go between the two programs (much like the 8-track format, which also used a moving head to access its four stereo programs).
Fidelipac today 
See also 
- "SCA Debuts Tape Cartridge Players". The Billboard 71 (7): p. 24. February 16, 1959. ISSN 0006-2510."The almost-square plastic-cased Fidelipac magazines, which come in three different sizes, are produced by the Fidelipac division of SAC [Stereophonic Automatic Corporation], located in Toledo, under the direction of George Eash, inventor of Fidelipac."
- James Wong. "A History". The Audio Circuit.
- The History of Recording Technology
- "New Fidelipac Tape Magazine Used in Radio". The Billboard 71 (37): p. 41. September 14, 1959. ISSN 0006-2510. "Conley Electronics Corporation, Skokie, Ill., granted a non-exclusive franchise for its Fidelipac continuous tape magazine to Collins Radio Company, Cedar Rapids, Ia. The Collins broadcasting division has incorporated the Fidelipac cartridge into its Automatic Tape Control record and playback units."
- Audio Engineer's Reference Book By Michael Talbot-Smith @ Googlebooks