The 7JP4 is an early black and white or monochrome cathode ray tube (also called picture tube and kinescope). It was a popular type used in late 1940s low cost and small table model televisions. The 7JP4 has a 7" diameter round screen which was often partially masked. Unlike later electromagnetically deflected TV tubes, the 7JP4 is electrostatically deflected like an oscilloscope tube.
The 7JP4 is part of the 7JPx series of circular face electrostatic cathode ray tubes (CRT). Originally developed for radar applications as a display device for radar display A scopes around 1944. [1] After World War 2 the CRT was adapted for television applications. There are three versions. The 7JP4 (P4 represents the phosphor that glows white and has medium persistence) for television. For oscilloscope applications the 7JP1 was used (P1 phosphor has a green trace and short persistence). Radar applications the 7JP7 was used (P7 phosphor has a blue-white trace with a long persistence). This CRT was produced by multiple manufacturers (RCA, General Electric, Sylvania Electric Products and Tung-sol). Except for the type of phosphor used all three are identical in operation and connection. The screen diagonal is 7 inches (17.8 cm) for 7JP1 and 7JP4, but only 5.5 inches (14 cm) for the 7JP7. [2]
Some General Electrical Characteristics are shown below. Second Anode + Grid 2 (Pin 9) and Plates (Pin 10 & 11 and Pin 7 & 8) have a maximum value limit of 6000 volts dc. Internal arcing can be expected when this voltage is exceeded. Actual values are typically in the 4000 to 5500 volt range, and some sets were operated as low as 2000 volts dc. Grid 1 (Pin 3) can receive either a Negative Bias or a Positive Bias. Pin-2 is the brightness voltage, and pin-3 is the video signal which rides on top of DC, and pin-2 is a DC Level which varies with the Brightness Control. Some sets are backwards and have pin-3 on ground and video on pin-2 along with brightness adjustment.
| Parameter | Value |
|---|---|
| Heater Voltage (Pin 1 and 14) | 6.3 Volts |
| Heater Current | 0.6 Ampere |
| Plates (Pin 10 & 11 and Pin 7 & 8) | 6000 Volts dc MAX |
| Cathode K (Pin 2) | 120 Volts dc |
| First Anode <Focus> (Pin 5) | 2800 Volts dc |
| Second Anode + Grid 2 (Pin 9) | 6000 Volts dc MAX |
| Grid 1 Negative Bias (Pin 3) | 200 Volts dc |
| Grid 1 Positive Bias (Pin 3) | 0 Volts dc |
| Grid 1 Positive Peak (Pin 3) | 2 Volts |
| Vertical Plate Deflection (Pin 10 & 11) | 216 Volts dc / inch (2.54 cm) |
| Horizontal Plate Deflection (Pin 7 & 8) | 177 Volts dc / inch (2.54 cm) |
From 1946 to 1951 the 7JP4 was a common CRT (Picture Tube or Kinescope) used in lower priced televisions sold in the United States. These television were popular for portable carry around and small table top sets. These smaller sets were direct view electrostatic deflection designs. This required an extremely high voltage to produce an image across the full display screen. In 1946, RCA influenced manufacturers (with royalty-free circuit designs) to move toward electromagnetic deflection type televisions. Electromagnetic deflection uses varying magnetic fields to produce a full screen image. Horizontal and vertical electromagnets are placed at the picture tube neck, called the "yoke". This method allowed the image to be viewed on larger screens. The first heavily mass-produced large picture tube to use this newer method of deflection was RCA's 10BP4, introduced in 1946. Soon after electrostatic picture tubes and the television electronic design would be completely replaced.
For a detailed look at US electrostatic TV design and the 7JP4 Kinescope from an Australian view (by cablehack) go to the external link below involving the Wards Airline TV (Sentinel model 400TV). [3]
The interest in the 7JPx series of CRT's is in restoration of dead technology. Dead Technology represent products that are no longer mass-produced or seriously used. The technology used in these designs have reach their highest level or have been replaced by a better technology. [4] [5] The restoration of early US made television sets has spurred interest in the 7JP4. Since this particular model is no longer made, only available ones are from old stock or from television sets that cannot be restored. This makes the price of a working CRT very expensive.
Because it is electrostatically deflected and was obsolete by the mid-1950s, most CRT testers will not test the 7JP4 and thus it is best tested in a working TV set. The Precision CR30, Sencore CR-70 and Jackson 707 are some of the CRT testers that are capable of testing the 7JP4,3KP4 and other electrostatic deflection CRTs. Since the availability of these CRT testers is very limited, the prices for such testers are steep, so many restorers test these CRT's on a working TV set that used electrostatic CRTs. There are many picture tube restoring equipment available for magnetic deflection tubes but there is no way to restore electrostatic tubes. The biggest problem with many picture tubes is the loss of emission or electron production due to contaminated or damaged cathode that surrounds the heater.
| The 7JP4 was used in the following sets (incomplete list): |
|---|
| Motorola VT-71 |
| Motorola VT-73 |
| Hallicrafters 504, 505, T-54 |
| Sentinel TV-400 |
| Sentinel TV-405 |
| National TV-7W |
| Philco 50-T701 & 50-T702 |
| Tele-Tone TV-149 |
These and other early television sets can be found in the "Collectors Guide to Vintage Televisions- Identification and Values", by Bryan Durbal and Glenn Bubenheimer ( ISBN 1-57432-126-9) published by Collector Books, Paducah, KY, USA. [6]
Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog signal.
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms (oscilloscope), pictures, radar targets, or other phenomena. A CRT on a television set is commonly called a picture tube. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer. The term cathode ray was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons.
The Selectron was an early form of digital computer memory developed by Jan A. Rajchman and his group at the Radio Corporation of America (RCA) under the direction of Vladimir K. Zworykin. It was a vacuum tube that stored digital data as electrostatic charges using technology similar to the Williams tube storage device. The team was never able to produce a commercially viable form of Selectron before magnetic-core memory became almost universal.
A television set or television receiver, more commonly called the television, TV, TV set, telly, tele, or tube, is a large device that combines a tuner, display, and loudspeakers, for the purpose of viewing and hearing television broadcasts, or as a computer monitor. Introduced in the late 1920s in mechanical form, television sets became a popular consumer product after World War II in electronic form, using cathode ray tube (CRT) technology. The addition of color to broadcast television after 1953 further increased the popularity of television sets in the 1960s, and an outdoor antenna became a common feature of suburban homes. The ubiquitous television set became the display device for the first recorded media for consumer use in the 1970s, such as Betamax, VHS; these were later succeeded by DVD. It has been used as a display device since the first generation of home computers and dedicated video game consoles in the 1980s. By the early 2010s, flat-panel television incorporating liquid-crystal display (LCD) technology, especially LED-backlit LCD technology, largely replaced CRT and other display technologies. Modern flat panel TVs are typically capable of high-definition display and can also play content from a USB device. Starting in the late 2010s, most flat panel TVs began to offer 4K and 8K resolutions.
Storage tubes are a class of cathode-ray tubes (CRTs) that are designed to hold an image for a long period of time, typically as long as power is supplied to the tube.
A monoscope was a special form of video camera tube which displayed a single still video image. The image was built into the tube, hence the name. The tube resembled a small cathode ray tube (CRT). Monoscopes were used beginning in the 1950s to generate TV test patterns and station logos. This type of test card generation system was technologically obsolete by the 1980s.
A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems. The word raster comes from the Latin word rastrum, which is derived from radere ; see also rastrum, an instrument for drawing musical staff lines. The pattern left by the lines of a rake, when drawn straight, resembles the parallel lines of a raster: this line-by-line scanning is what creates a raster. It is a systematic process of covering the area progressively, one line at a time. Although often a great deal faster, it is similar in the most general sense to how one's gaze travels when one reads lines of text.
Large-screen television technology developed rapidly in the late 1990s and 2000s. Prior to the development of thin-screen technologies, rear-projection television was standard for larger displays, and jumbotron, a non-projection video display technology, was used at stadiums and concerts. Various thin-screen technologies are being developed, but only liquid crystal display (LCD), plasma display (PDP) and Digital Light Processing (DLP) have been publicly released. Recent technologies like organic light-emitting diode (OLED) as well as not-yet-released technologies like surface-conduction electron-emitter display (SED) or field emission display (FED) are in development to replace earlier flat-screen technologies in picture quality.
Rear-projection television (RPTV) is a type of large-screen television display technology. Until approximately 2006, most of the relatively affordable consumer large screen TVs up to 100 in (250 cm) used rear-projection technology. A variation is a video projector, using similar technology, which projects onto a screen.
The Chromatron is a color television cathode ray tube design invented by Nobel prize-winner Ernest Lawrence and developed commercially by Paramount Pictures, Sony, Litton Industries and others. The Chromatron offered brighter images than conventional color television systems using a shadow mask, but a host of development problems kept it from being widely used in spite of years of development. Sony eventually abandoned it in favor of their famous Trinitron system using an aperture grille.
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