The 7JP4 is an early black and white cathode ray tube used in late 1940s televisions. It 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.
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. One notable exception is the Jackson 707 Cathode Ray Tube Analyzer which is capable of testing the 7JP4 along with the 3KP4 and other electrostatically deflected CRTs.
The 7JP4 was used in the following sets (incomplete list):
