Dec. 1, 1953 H. R. SMITH 2,561,443 TELEVISION’ KEYSTONE BALANCE CONTROL CIRCUIT Filed D60. 30', 1949

32 33

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Fig. 3 a Fig. 3b

Fig. 4 b FI9’. 4 a INVENTOR. I HARRY R. SMITH ‘Patented Dec. 1, 1953 2,661,443

UNHTED sTATss PATENT orrics 2,661,443 TELEVISION KEYSTONE BALANCE CONTROL CIRCUIT Harry R. Smith, Glen Ridge, N. J., assignor to Allen B. Du Mont Laboratories, Inc., Passaic, N. J ., a corporation of Delaware Application December 30, 1949,‘Serial N 0. 136,092 3 Claims. (01. 315-24) 1 This invention relates to an electrical circuit Figure 3b shows the normal rectangular pat for producing a predetermined pattern on the tern produced on the screen of an iconoscope type screen of a cathode ray tube. It relates par cathode ray tube by a de?ection current of the ticularly to circuits for distorting the raster on type shown in Figure 3a; cathode ray tubes having off center electron guns Figure 4a shows a horizontal sawtooth current such as iconoscope tubes, certain projection wave with a vertical sawtooth wave added; and tubes, and tubes of the type disclosed in U. S. Figure 4b shows the pattern produced on the Patent 2,480,848. face of a standard cathode ray tube when stand Throughout this speci?cation the term “icono ard de?ection currents are applied to a yoke in scope type cathode ray tube” will be used to de 10 which the magnetic ?elds are not at right angles note any cathode ray tube having an off center to each other. electron gun. In Figure l a horizontal transformer II is The keystone pattern of iconoscope type tubes shown having its primary I2 connected to a is familiar to those skilled in the art. To cause source is of horizontal voltage, and its second the pattern to assume a normal rectangular ary It connected to one end of a horizontal de shape it is necessary to introduce correcting ?ection coil IS. The other end of the secondary voltages into the de?ection ampli?ers. The cor It is connected to a tap I‘! on the keystone bal recting voltage for the horizontal ampli?er may ance control I3. The contact arm IQ of this be a sawtooth voltage at the vertical frequency potentiometer is connected to the contact arm which is used to modulate the horizontal de 2I of the horizontal positioning control 22. A ?eeting voltage before it passes through the hori tap 23 on this control 22 is connected to the zontal output transformer. It is necessary for other end of the horizontal de?ection coil It. the horizontal output transformer to pass the The control 22 is connected across a source 24 of comparatively low vertical frequency without horizontal positioning current which is shown distortion as well as harmonics of the horizontal here as a battery. frequency, up to about the tenth, in order that The keystone balance control I 8 is connected such a system may operate properly. across the secondary 26 of a transformer 21, This invention consists in adding a controlled which maybe an audio transformer having its current, varying at the vertical frequency, to the primary 28 connected to a vertical de?ection saw horizontal de?ecting current ?owing through tooth signal- generator 29. A capacitor 3| is the horizontal de?ecting coils. connected from the center tap I ‘I of the keystone An object of this invention is to provide an control I8 to ‘the center tap 23 of the horizontal improving mixing circuit. positioning control 22 to provide a low impedance Another object is to provide an improved key path between these points for the high frequen stone correction circuit for use with cathode ray cies in the horizontal de?ection wave. tubes having on" center electron guns. Under normal operating conditions of the cir Another-‘object is to correct for de?ciencies in cuit in Figure '1 the horizontal voltage source I3 the de?ection yoke of magnetically de?ected presents a de?ection voltage of the type indi cathode ray tubes. cated by reference character 32, to the primary Still another object is to compensate for the winding I2 of the output transformer I I. This limited frequency response of transformers. 40 voltage wave 32 is preferably an equally mod Further objects will be apparent to those skilled ulated horizontal de?ecting wave, so that in pass in the art after studying the following speci?ca ing through the transformer II it will not be tion and drawings in which: distorted and the resulting current wave 33, as Figure 1, partly in schematic and partly in shown in Figure 2a, ?owing through the sec block diagram form, shows one embodiment of 45 ondary It of the transformer II will also be the invention; symmetrical. This wave, ?owing through the Figure 2a shows a horizontal sawtooth cur horizontal de?ection coils I6, would normally be rent wave modulated unequally by a vertical saw expected to produce a pattern such as is shown tooth wave; in Figure 2?) on the face of the iconoscope type Figure 2b shows the pattern on the face of an 50 tube. However, non-symmetrical yoke or tube iconoscope type cathode ray tube when a de construction frequently results in a raster such ?ection current such as that shown in Figure 2a as is shown in Figure 3b. is used; The vertical signal source 29 causes a sub Figure 3a shows the desired de?ection current stantially sawtooth current wave 34 to ?ow in a for an iconoscope type cathode ray tube; secondary 26 of a transformer 21. If the contact 2,661,443 4 19 on the potentiometer I8 is rotated so as not oscillations is the same. The current wave-form to be electrically contiguous with the tap I1, a through the coils I6 is shown in Figure 4a with portion of the current 34 will be diverted to ?ow the vertical saw component added. through the secondary l4 and the coils IS. The It will be apparent that modi?cations of the amplitude and direction of ?ow of the diverted invention may be made, the scope thereof being portion of the current 34 are determined by the de?nedby thefollowing claims. direction and amount of rotation of the contact What is claimed is: l9 from the zero point; i. e., the point at which 1. In a television de?ection circuit for a cath it makes direct electrical contact with the tap ode ray tube having an off center electron gun, H. The addition of the current 34 to the equally 10 a source of horizontal de?ecting voltage, a hori modulated current wave 3.3 shown in Figure 2a zontal output transformer having a primary and results in the non-symmetrical current wave I33 "a secondary winding, said primary being con shown in Figure 3a. If the proper amplitude and. nected to said source of voltage, a horizontal de polarity of the current 34 is added to the cur: flectioncoil, one end of said de?ection coil being rent 33, the resultant current 33 will counter: connected to _,,a ?rst tap on said secondary wind act the non-symmetrical yoke or tube construc-' ing, a source of vertical de?ection voltage, a ver tion and produce the desired, rectangular raster tical output transformer having a primary and as shown in Figure 2b. a ,s‘ecgndary winding, said primary of said ver Similarly the amount and direction of the D. tical transformer being connected to said source C- positiohing current flowing through the coils 20 of vertical deflection voltage, an impedance con 16 due to the direct current flowing through the nected in series with said secondary winding on potentiometer 22 are controlled by the rotation said vertical output transformer, a second tap of the contact 2| with respect to the tap 23. on said secondary of said horizontal output The highfrequencies of‘th'e horizontal de?ect transformer being‘ connected to a point on said ing current are bypassed by means of the con 25 impedance, the other end of said de?ection coil denser ,31 and do not ?ow' through the poten being connected to another point .on said im pedance. tiometers 22 and I8. - ' ' Although the potentiometer I8 is shown with 2. The circuit of claim 1 in which one of said a tap ll intermediate the ends thereof, this is a points on said impedance is variable with re matter of convenience only since, if the desired 30 spect to the other oisoid points. polarity of the additional current through the ' 3. In a television de?ection circuit, a plurality coils I6 derived from the current 34 is known, it of sources of deflection voltages, a ?rst trans would be possible to connect one end of the sec. ,fprmer having a primary and a secondary wind ondary M to one end of the potentiometer I8 ing, said primary winding- being connected to a instead of to the tap ll. In such case, only the 35 ?rst said source of de?ection voltage, a de?ec amplitude of the additional current through the tion ‘coil, one end of said coil being connected to coils [6 could be controlled by the rotation of a ?rst tap on said secondary winding, a second the contact IS). The polarity would always re transformer having a primary and a secondary main the same. v'I‘he positioning circuit com Winding, said primary of said second transformer prising the potentiometer ‘2g and the voltage 40 being connected to a second Said source of de source 24 has been inserted for purposes of illus ?ection voltage, an impedance connected in “when with known circuit elements and are not series with said secondary winding of said second necessary to the operation of this invention. For transformer, a second tap on said secondary of instance, if no positioning were necessary, the said ?rst transformer connected to ,a point von contact I9 could be connected directly to the said impedance, the other ,end of said de?ection junction of the condenser 3! and the coils H5. coil being connected to another point on said The raster in Figure 4b is the result of having isles-dense the vertical de?ection soils rotated clockwise ias ‘ sun? viewed from the face of a standard cathode ray tube) with respect to the horizontal de?ection References Cited in the ?le of this patent soils The circuit of Figure .1 may be used to UNITED ‘STATES PATENTS overcome this type of distortion iust as it was Number Name Date used to counteract the keystone distortion. :In 1,485,727 Sindeband __,_..._,_____ Mar. 4,1924 this case the voltage wave 32 supplied by the 2,477,557 Torsch _,_---,------July 26, 1949 horizontal signal source 131s not modulated and 2,505,011 Smyth ______,_i Apr. 25, 1950 the amplitude of each of the ‘horizontal voltage