NAEB Engineering Newsletter (June 1, 1958)

A E B m Engineering Newsletter NATIONAL ASSOCIATION OF EDUCATIONAL BROADCASTERS 14 GREGORY HALL JUNE, 1958 URBANA, ILLINOIS TV TECHNICAL TIPS (April) —Cecil S. Bidlack The first week in March I spent at Redwood City, Calif. Here I had the opportunity to take the five- day factory training course covering the operation and maintenance of the Ampex Videotape Recorder. Three days were devoted to the study of schematics and block diagrams of the various chassis employed in recording the video and audio signals of a TV pro¬ gram on magnetic tape. For the last two days of the course, the students go through the setup procedure r as outlined in the comprehensive instruction manual furnished with each recorder. r , The Ampex Videotape Recorder consists of two standard racks of electronic equipment and' the con¬ sole, which contains the transport mechanism and other electronics. All rack and console wiring is com¬ pleted at the factory. In fact, the racks are bolted together and shipped that way. Each recorder is placed in operation and given a final test at the fac¬ tory to see that it meets operating specifications be¬ fore shipment. When the equipment arrives at its destination and is uncrated, installation consists of hooking it up to the 60-cycle AC power circuits, mak¬ ing video connections and the rack-to-console wiring. This latter wiring is a very simple job with only three interconnecting cables involved', two of which termin¬ ate in factory-mounted spade type terminal strips which connect to appropriate terminals in the end of the console. The third cable contains ten coaxial cables which require soldered connections to the proper console terminal. Once these connections are made, you are ready to begin the initial check-out pro¬ cedure which is detailed step by step in the instruc¬ tional manual. For proper set-up and maintenance, a dual trace is required on the test oscilloscope. Ampex recommends NAEB Engineering Newsletter June, 1958 NAEB Engineering Newsletter, a quarterly publication issued by the National Association of Educational Broadcasters, 14 Gregory Hall, Urbano, III. $2 a year, edited by Cecil S. Bid- lack. a Tektronix Model 541 with a dual input pre-ampli¬ fier and also a high gain pre-amplifier unit for certain other tests. A reference tape for initial tests is sup¬ plied with each unit as well as a micrometer depth gauge for measuring head protrusion from the rota¬ ting drum. A standard test tape is being developed which will be supplied with all machines. Degaussing is accomplished at present with the conventional bulk type unit now used for erasing audio tapes, since the recorder has no erase head. An accessory unit is now being developed which will make degaussing an auto¬ matic process for consistent erasure. The recording tape has been vastly improved over that orginally used. At one time rejections sometimes ran over 90 per cent of the tape supplied to the user. At present there is only one method of testing the tape and that is by recording a video signal and play¬ ing it back. This practice is recommended when a new reel of tape is received. We used one reel of tape for tests during the week, erasing it manually when the occasion demanded. I saw no evidence of drop¬ outs, which were once the major defect making the tape unfit for use. To enable the tape to be spliced, an “edit” pulse is laid down along the bottom edge of the tape over the control track. These pulses are “developed” by applying a carbonyl iron powder suspended in a volatile fluid to the coated side of the tape. This so¬ lution dries rapidly and the tape is cut by the use of 1