Carts, all about the Audio Cassette Standard

The NAB cart cassettes - here with the
brand name Fidelipac, but they were
also manufactured by brands such as
ITC, Harris, Audicord, Gates, Ampro.

The Spotmaster 500 B rec / play unit

Inside view of the cart-lookalike but
not fully similar Eight-track cartridge.
The most important difference is that
the eight-track had integrated pinch
roller, seen on top right on this image.

The NAB "Cart" Audio Cassette standard
This audio tape cassette format was developed and introduced by Collins Radio in 1959, and the same year introduced as a standard at the NAB - National Association of Broadcaster's 1959 annual show. Collins Radio were reputed for their high quality broadcasting studio consoles and their transmitter gear for military and amateur use. The cassette standard was in the beginning limited to mono single-track audio - later updated for stereo sound capability. Along with the audio track(s) there were a separate inaudible track for the 1 kHz cue tone which automatically triggered the playback into stop mode, then setting the cassette cued and ready for next instant start of the same recorded material . The automatic cue function could also be used for secondary relay start of another player with another commercial, jingle, or other short recorded item. More modern machines also involved count down timers displaying the exact remaining time of the recording.

In 1959 the first machines for this cassette standard was introduced by BE - Broadcast Electronics under the product name "Spotmaster 500" - is the handbook for this first machine. The Spotmaster 500 became a trusted tool and to some users the name Spotmaster also became a synonym for the cassette itself, but actually the name Spotmaster is a brand name that the company Broadcast Electronics used on a large product programme with studio consoles and more, all under the brand name Spotmaster. So, to make less confusion the cassettes should be called "carts" or preferably "nab carts".

Before the cart machines were introduced, the practice for playing recorded spots involved use of either reel to reel tapes or pre-recorded vinyl discs. A recording of KLIF, Dallas Texas, give us a recall of how the noisy crackly discs could sound in a broadcast in the beginning of the sixties :
The Ken Lock show. January 4, 1961

Two months after the above broadcast, the Swedish offshore station Radio Nord from March 8, 1961, started their operations from the Baltic Sea outside Stockholm and became the first broadcast company in the world to use the Spotmaster 500 as their standard machine for jingles and commercials. Radio Nord could start from square one producing their own jingles and commercials in their own studios, unlike the American radio stations, so related to other partners within the broadcast industry where all involved had to undergo a total change from one industry standard to a completely new.

The nab cart cassette was very similar to the Stereo-8 cassettes, often named as the eight-track cartridge, eight-track tape, or simply eight-track. This car stereo related standard was introduced in 1965 as an American competitor to the European Compact Cassette (CC) introduced by Philips in 1963. The Stereo-8 standard was developed by a consortium where the largest companies were Ampex, Ford Motor Company, Motorola, and the RCA Victor Records Company.

Unlike most other cassette tape standards the tape wasn't running from one reel to another. Instead they used only one single reel containing a continuous endless loop of 1/4-inch recording tape specifically prepared so that the tape were able to slip out from its inner round of the tape spool. On the back side of the magnetic tape, opposite to the magnetic layer, there were a surface of graphite as a dry lubricant making the tape able to easily slip out with very low friction. To make this possible it was also important that the tape was wound very lightly "airy" tensed on the spool . This, however didn't have to mean that the tape would slack inside the cassette because the tape around the hub had a lower linear velocity than the tape at the outside of the reel, so the tape layers would slip very lightly past each other.

When playback was started, the tape was lightly pulled out from the center of the spool and then it passed by the opening holes at one end of the cartridge where the magnetic head is "looking in through the window" in contact with the tape and the tape forwardly passes by the pinch roller / capstan and then the tape is wound back onto the outside of the spool. The spool was freewheeling - its rotation was driven only by the tape going out and then returning to the spool, and the only parts driving all of this was the pinch roller and the capstan. It was a very uncomplicated tape recorder construction depending on very few moving parts. The only disadvantage was the lack of fast winding abilities; it was technically impossible to rewind the tape, and the only way to make fast forward were by just speeding up the motor in playback mode while cutting off the audio.