The 7JP4 is an early American television picture tube, which was built in the late 1940s. Your screen diameter is 18 cm, the screen light color is white. Under the name 7JP1 an identical tube with green screen Display color was available, which was primarily used in measuring devices. In contrast to conventional television picture tubes with magnetic deflection, the deflection of the electron beam takes place electrostatically. The 7JP4 is thus actually the oscilloscope CRTs closer than the television picture tubes.
For electrostatic deflection, a voltage between 600 and 900 volts is required, it almost no current flows. The anode voltage of 6 kV. The angle of deflection is limited to max. 40 ° which is reflected in a correspondingly long tube of almost 40 cm. Picture tubes with magnetic deflection work with deflection angles of 70 °, 90 ° and 110 ° and therefore are much shorter. A TV with a 7JP4 comes out because of the small deflection power with only 100 W, while a television in this era, it brought with magnetic deflection up to 300 W.
Although just under 18 inches of screen size was relatively small and many television viewers used to some extent even filled with water magnifying glasses, made possible the comparatively inexpensive 7JP4 in the 1940s, television in the United States the breakthrough as a mass medium. So television could be sold with the 7JP4 for under U.S. $ 200, equipment with nearly 8 cm screen diagonal could be had for under $ 100. An average monthly wage at this time was about 150 U.S. dollars.
The 7JP4 was used among others in the following device models:
- Motorola VT 71, VT -73
- Hallicrafters 505
- Sentinel TV -400, TV -405
- National TV -7W
- Philco 50 - T701, T702 - 50