FIRE VOLTAGE TRACK CIRCUIT The invention relates to a focus voltage correction configuration for a cathode ray tube. An image displayed on a cathode ray tube (CRT) may suffer imperfections or distortions such as blurring, or non-linearity that is incident to beam scanning on the cathode ray tube. Such imperfections or distortions occur because the distance of the electron gun from the cathode ray tube to the faceplate varies markedly as the beam deflects, for example, in the horizontal direction. Commonly, reducing the blurring that occurs as the beam is deflected in the horizontal direction can be obtained by developing a dynamic focus voltage that has a parabolic voltage component at the horizontal velocity and applying the dynamic focus voltage to an electrode. focus of the cathode ray tube to dynamically vary the focus voltage. In the projection television receiver (PTV), the blue phosphor of the cathode ray tube screen has a significantly lower persistence than the green or red phosphorus. To compensate for the difference in persistence, the instantaneous brightness of blue phosphorus becomes significantly higher than that of green or blue phosphorus. Due to the higher instantaneous brightness, blue phosphorus saturates at high video excitation levels. Thus, the light output does not increase in blue as the video driver increases. In contrast, the light output in the red and green phosphors continues to increase as the video exciter increases. The result is yellow in the high light areas formed on the screen. It may be desirable to obtain a high image brightness for a given cathode ray tube. Therefore, typically the blue focus is placed to be slightly out of focus to increase the size of the blue beam spot. The increase in the size of the beam point increases the minimum saturation level and allows a brighter blue and an increased linear blue exciter range. A light blur of blue is acceptable. This is because the human eye can not focus on blue and red at the same time and most of the details of images are transmitted in red and green. Beam current changes caused by video loading cause variations of the final accelerator voltage. Despite having defocused blue in most areas of the image, in some areas of the image the focus can remain optimal, when the focus voltage does not track the final accelerator voltage. It may be desirable to maintain a consistent blur throughout the image. Therefore, it may be desirable to cause the creep of the focus voltage to change in value by maintaining a constant ratio of the focus voltage to the final accelerator voltage of, for example, 1/3. If this relay tracking requirement is not met everywhere in the image, there will be portions of the image where the changes in the final accelerator voltage with respect to the blue focus voltage will produce a focus of ideal blue undesirable. This will cause saturation of the blue phosphorus and a lack of desired blue brilliance may occur. The affected areas will appear as undesirable yellow horizontal stripes in white areas. It may be desirable to provide a tracking of the final accelerator voltage ratio to the focus voltage so that the blue image can be defocused uniformly to obtain increased brightness with minimal yellow in the white areas. In a prior art, tracking of final accelerator voltage ratio to focus voltage was obtained by applying a portion of the final accelerator voltage to an input terminal of a dynamic focus amplifier so that a sample of the final accelerator voltage is sum in the amplifier with dynamic focus signals d. So, a composite signal developed in an output terminal of the amplifier is coupled to the focus electrode of each cathode ray of the television projection receiver via dynamic focus coupling capacitors. In a video image forming apparatus, which shows one modality of the invention, a cathode ray tube includes a final accelerator electrode and a focus electrode. A high-voltage energy minister is used to generate a high-voltage final accelerating voltage at the final accelerator electrode and a high-voltage focus voltage at the focus electrode. A passive network has a first terminal in which the final accelerator voltage is developed and a second terminal where the focus voltage is developed. The passive network includes a first capacitance for capacitively coupling a voltage jitter component from the final accelerator voltage to the focus electrode. In the drawings: The single figure illustrates a dynamic focus generator, which shows an aspect of the invention for a cathode ray tube. T-a Single figure illustrates a cathode ray tube 10 of a television projection receiver. The cathode ray tube 10 produces a blue image and has a final accelerator electrode 14 coupled via a protective resistor 152 to a final throttle voltage supply terminal 12 of a conventional high voltage power supply 11. The other two cathode ray tubes of the television projection receiver are not shown. The power supply 1 1 includes a return transformer 13 coupled to an output stage of the conventional horizontal deflection circuit 30. The transformer 13 has a segmented high-voltage winding 15. A final throttle voltage U developed at terminal 12, Approximately 30KV direct current (DC) voltage develops from a return pulse voltage FB that is rectified. A final accelerator filter capacitor 1 51 is coupled to the terminal 12. The capacitors 151 and the resistor 152 can be included in a module, not shown, that distributes the voltage U to each of the receiver's cathode ray tubes. of television projection. The pulse voltage FB is developed from the sum of the return pulse voltages of all the winding segments 15. A focus voltage generator 16 includes approximately one third of the winding turns of the winding 15. The generator 16 produces a high voltage F of about 1 1.5KV CD of the pulse voltage portion FB developed in one third of the winding turns of the winding 15. The voltage F is developed in a terminal 31 of a resistive voltage divider 37 having a resistance very high. A dissipator resistor 150 is coupled between the terminals where the voltages V and F are developed. The voltage divider 37 includes a resistor 32, a potentiometer resistor 33, a resistor 34, a resistor 35 and a resistor 36, coupled in series in that order. The terminal 31 forms an end terminal of the resistor 32. An end terminal 36a of the resistor 36 is coupled to a reference voltage, termed as ground. A DC voltage component of a focus voltage FV is developed from the voltage F at a terminal 38 of the resistor potentiometer 33. The DC voltage component of the PV voltage is coupled to a focus electrode 17 of the cathode ray tube 10 via a resistor 39. The DC voltage component of the focus voltage FV is adjustable in a voltage range of approximately 1.5 KV to facilitate adjustment of the focus voltage. A dynamic focus correction signal DF is developed in an output terminal 22 of a conventional dynamic focus signal generator 23. An example of the generator 23 is described in the U.S. Patent Number of North America. Series 5,430, 358 entitled "Amplifier of High Voltage Vertical Dynamic Spotlight "in the name of John B. George, the generator 23 may include an amplifier stage not shown.The generator 23 receives a horizontal speed parabola signal HP and a vertical velocity parabola signal VP and combines Parabolic signals The DF signal includes a sum of a horizontal velocity parabola component signal of 800 V pp and a vertical velocity parabola component signal of 300 V pp at a fundamental frequency of, for example, 60 Hz. The signal DF is coupled via a capacitor 24 to the focus electrode 17 of the cathode ray tube 1 0. The capacitance value of the capacitor 24 is selected such that in combination with the resistance developed in a junction terminal 40 of resistor 39 and capacitor 24, there is negligible signal attenuation and minimal phase shift at the 60 Hz velocity of the vertical velocity parabola component signal. However, said configuration forms a low pass filter which prevents voltage fluctuations produced at the voltages U and F, as a result of the video load, at the focus voltage FV. The low-pass filtration mentioned above provides no additional benefit in that an inherent distortion is eliminated by using the one-third portion of the winding 1 5. In accordance with one aspect of the invention, a capacitor of 1 50pF 25, coupled in series with a resistor of 1 Mega Ohm 26, together they form a network of resistor-capacitor (RC) 41 which is coupled between the terminal of the final accelerator voltage 12 and the focus electrode 17. Conveniently, the resistor-capacitor network 41 is applied only to the focus electrode of the cathode ray tube 10, which produces the blue image. The focus voltage generators, not shown, of the cathode ray tubes that produce the green and red images, not shown, are similar to the focus voltage generator 16 except that they do not include a network such as network 41. The dynamic focus signal DF of the generator 23 is voltage divided capacitively by a capacitive voltage divider formed by the capacitors 24 and 25. The components of the dynamic focus signal at low frequencies in the range of 60Hz to 1 KHz are attenuated in the focus electrode 1 7 to approximately 2/3 of its values. Voltage fluctuations in the frequency range 60Hz to 1 KHz of the final accelerator voltage U caused by the video load are divided into voltage downward in the voltage divider consisting of resistor 26, capacitor 25 and capacitor 24 by a division ratio of 1/3. As a result, 1/3 of the amplitude of the voltage fluctuations of the end-of-throttle voltage is applied to the blue focus electrode 1 7 to provide optimum tracking of the focus voltage FV with respect to the voltage U. As explained above, if the tracking requirement was not met in all parts of the image, there could be portions of the image where, due to changes in the final accelerator voltage, the blue FV focus voltage could cause a focus undesirable ideal. The result is that phosphor saturation and a lack of desired blue brilliance can occur. For the signal components of the dynamic focus signal at frequencies above 1 KHz, the resistor 26 of 1 Meg becomes dominant and large with respect to the reactance of the capacitors 25 and 24, and stops the action of dividing. Therefore, conveniently, for a dynamic focus signal component of horizontal speed at 15 KHz there is a negligible attenuation. The induced voltage fluctuations of the video signal become smaller for these frequencies and may not require tracking of voltage fluctuation of the focus voltage with respect to the final accelerator voltage. During the arc of the image tube, the supply terminal 12 is grounded quickly and temporarily. Conveniently, the resistor 26 of 1 Meg protects the dynamic focus signal generator 23 from damage due to large currents that would flow in the capacitors 24 and 25 if the resistor 26 were not present.