page_title: 7JP4
section_title: Development
hierarchical_section_title: 7JP4 / Development
caption_attribution_description: English: 7JP4 picture tube was used extensively in small low cost televisions made and sold in the United States during the late 1940's. It is electrostatic in design, soon made obsolete by electromagnetic deflection television.
context_page_description: The 7JP4 is an early black and white or monochrome cathode ray tube. 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.
context_section_description: 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. 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.
caption: Side View of 7JP4
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