Focus voltage control arrangement

A video imaging apparatus, comprising:

• a first cathode-ray tube having a first ultor electrode and a first focus electrode, and a second cathode-ray tube having a second ultor electrode and a second focus electrode;
• a power supply for generating an ultor voltage coupled to said first and second ultor electrodes having a fluctuating voltage component produced by beam current variations;
• a high voltage amplifier for generating a dynamic focus voltage component at a frequency related to a deflection frequency;
• a combining network for combining said fluctuating voltage component and said dynamic focus voltage component to develop a combined, dynamic focus voltage;
• a first voltage divider responsive to said combined, dynamic focus voltage for developing from said combined, dynamic focus voltage a first dynamic focus voltage at said first focus electrode;
• and
• a second voltage divider responsive to said combined, dynamic focus voltage for developing from said combined, dynamic focus voltage a second focus voltage at said second focus electrode.

A video display apparatus, comprising:

• first and second kinescopes, each including ultor, electron beam modulation, and focus terminals, for generating electron beams impinging on display screens;
• a deflection arrangement for deflecting said electron beams across at least a portion of said display screens of said first and second kinescopes;
• a source of image signals coupled to said electron beam modulation terminals of said first and second kinescopes, for modulating said electron beam with image information synchronized to said deflection, for defining at least components of an image on said display screens;
• a single source of ultor voltage coupled to said ultor terminals of said first and second kinescopes, said source of ultor voltage being subject to variation in said ultor voltage in response to said modulation of said electron beams;
• a single source of direct first focus voltage directly coupled to said focus terminals of said first and second kinescopes, said first focus voltage being generally in a fixed proportion to said ultor voltage;
• a single source of second focus voltage responsive to said deflection of said electron beams;
• and
• coupling means coupled to said source of ultor voltage and to said source of second focus voltage, for coupling said sources of ultor and second focus voltage together and to said focus terminals of said first and second kinescopes in an amount related to the frequency components within said ultor and second focus voltages.

A television apparatus, comprising:

• first, second and third picture tubes, each including an ultor terminal and a focus terminal;
• a source of ultor voltage coupled to said ultor terminals of said first, second, and third picture tubes, said ultor voltage tending to change in response to flow of beam current in said picture tubes;
• a source of first focus voltage which tends to maintain a value which is a constant proportion of said ultor voltage, said source of first focus voltage being coupled to said focus terminals of said first, second, and third picture tubes;
• deflection means for deflecting said beams vertically and horizontally;
• a source of dynamic focus voltage which produces vertical- and horizontal-rate dynamic focus signals in response to said deflection;
• a coupling circuit including a first input terminal coupled to said source of ultor voltage, a second input terminal coupled to said source of dynamic focus voltage, and also including an output port coupled to said focus terminals of said first, second, and third picture tubes, for summing together and applying to said focus terminals of said first, second, and third picture tubes (a) a first proportion of said dynamic focus voltage having frequency components lying below a first frequency, (b) a second proportion of changes in said ultor voltage, and (c) a third proportion of said dynamic focus voltage having frequency components lying above a second frequency, greater than said first frequency.