Thursday, May 3, 2012

Cart Snarl Blooper, By Dave M.

In the 70's, tape cartridge technology was good enough to record the music on endless loop carts, for airplay. Playing "records" on the air was beginning to give way to new technology. Records, after all, could get scratched, could develop noise resulting from dust and dirt in the grooves, and might even break if dropped or mis-handled. Frequently played records would have to be replaced, sometimes as frequently as once a day because of some sort of sonic defect. Tape cartridges would solve most of these problems.

The endless loop tape cartridge was a derivative of 8 track tape cartridges, except it used high quality studio grade lubricated tape, and specialized tape decks created specifically for broadcast use. That's what was done at ITC, International Tapetronics Corporation, where I went as service manager after my tour of duty at KAAY.

When carts were used on the air, there was always the danger that a cart would "die" on the air. The example KLPQ blooper was what it sounded like when a cart failed and the DJ was not in the room or otherwise not paying attention: Moments of nervous dead air, then the panicked scramble to get things corrected.

The ScotchCart was introduced that took tape cartridge recording and playback about as close to studio grade reel to reel performance as was possible with the technology of the time - direct A-B comparisons between the original material and the playback version of a ScotchCart were usually undistinguishable, even for the fabled "golden ears' always present in the studio.
(ITC Series 99 Professional analog audio tape cartridge record / playback deck)

The ScotchCart was the best analog audio tape cartridge we had ever seen.  It was sonically transparent, mechanically rugged, and performed superbly in the often rough and tumble control room environment . And best of all it was a match for the ITC Series 99B analog audio tape cartridge machines that were our top or the line recorders and playback decks.

(ScotchCart audio tape cartridge)
But the ScotchCart had one very big problem. It would run for literally hundreds of plays beyond that of a traditional tape cartridge, and then without any warning whatsoever it would fail, usually at the worst possible moment. Since I ran the service department at ITC the telephone calls ultimately ended up on my desk. And there were a lot of P.O.'ed engineers I had to deal with.
We spent huge amounts of man-hours researching the cartridge failure mechanism. We discovered the failure mode, and from that we then developed a resolution strategy. We decided to develop the means to dynamically measure the cartridge playback performance in real-time, and display the cart performance in bar graph form. We used a "red-yellow-green" LED bar graph display that could be easily read at a distance. The idea was that if we could give the DJ an indication that the cartridge was beginning to fail, and how soon till disaster strike, he could pull the cart out of circulation until a new, replacement cart could be made and substituted.

Today, most radio playout is done from digital databases, and audio tape cartridges are used only on a limited basis, if at all.


  1. Hollis W. DuncanMay 3, 2012 at 4:43 PM

    The endless-loop cart was invented by Bill Lear (of Lear Jet fame) to provide music in an automobile. It didn't take long for broadcasters to catch on.

    My first engineering job was in 1971 at KALO-1250 in Little Rock. New Owner Bernie Mann wanted to replace KALO's ancient cart machines and some kind soul recommended ITC. After a career of working with Spotmasters, they were wonderful.

    So, why didn't we install ITC machines at KLAZ? That was one of many technical arguments that I lost. Manager Joe Dickey was heavily into imitating KAAY and KAAY had Spotmasters, so that's what he bought for KLAZ. It did not work out well.

    The very first broadcast cart machine was homebuilt at KLCN-910 in Blytheville, Arkansas. Then-engineer Joe Nearns acquired a cart deck mechanism from Viking and added the circuitry to start and stop the deck remotely. These machines were cued using piece of metal foil glued to the tape at the starting point. Joe published his design in Broadcast Engineering magazine around 1962.

    We inherited these machines at KAWW-1370 in Heber Springs in 1967 and they were still working just fine. However, the foil tape couldn't be removed and it was necessary to find a cart that was divided up like you needed (for instance, a 5 1/2 minute cart divided into one-minute segments or 30-second segments).

    1. Mr Duncan, did you know my father Joe Nearns personally?
      Bobbie Jo Nearns

  2. And a comment sent to me by Paul Kirby:

    "Bud, We had our semi-annual San Antonio air personality/engineer luncheon today, where I got to speak with a a number of old time broadcast engineer types from the 50s and 60s about the following Dave M. comment from the KAAY 1090 blog: The endless loop tape cartridge was a derivative of 8 track tape cartridges, except it used high quality studio grade lubricated tape All of the engineering types strongly state that the 8 track tape cartridge was developed from the 4 track tape cartridge which was developed from the endless loop broadcast cartridge technology of the 50s. Still enjoying reading the blog. Paul"

    (Search 'Paul Kirby', who is one of the renowned broadcasters mentioned in San Antonio Radio Memories....thanks, Paul! bs)

  3. Paul Kirby et. al. are absolutely correct. My writeup was only intended to be a coarse overview primarily for people not familiar with the cartridge tape technogy. It was after all a cart that failed in the KLPQ air check and i was attempting to explain how it might have happened. If you read it too closely you may miss the reason for the comment.

    In fact, my mentor at ITC was Jack Jenkins, who held most of the cartridge and cart machine patents at that point in time. If anyone is interested, I can upload the technical history of the development, along with the major milestones and accomplishments along the way.

    Too much fine detail sometimes causes one to lose track of the main point and center thesis. It was a cart failure after alll. Heh!