CRT With internal thermionic valve for high voltage control

A split anode penetration cathode ray tube comprising:

• an evacuated envelope including funnel and faceplate portions;
• electron gun means for producing an electron beam to strike the faceplate;
• a conductive layer of beam penetration phosphors, located upon the interior surface of the faceplate poriton of the envelope, for producing a visible indication at the location of the impact of the electron beam upon the faceplate;
• a conductive coating upon the inside surface of the funnel portion of the envelope for accelerating the electron beam toward the faceplate, the conductive coating electrically isolated from the conductive layer of beam penetration phosphors;
• a cathode for emitting electrons;
• plate means, electrically connected to the conductive layer of beam penetration phosphors, for attracting the electrons emitted by the cathode, and for controlling the magnitude of the voltage applied to the conductive layer of beam penetration phosphors;
• grid means, located between the cathode and the plate means, for controlling the quantity of emitted electrons reaching the plate means;
• a source of high voltage;
• a first resistance connected between the source of high voltage and the conductive layer of beam penetration phosphors;
• a second resistance connected between the source of high voltage and the conductive coating inside the funnel portion;
• and
• control means, coupled to the grid means, for controlling the voltage applied to the conductive layer of beam penetration phosphors.