US2470197A - Electron beam deflection control system - Google Patents

Description

May 17, 1949. c. E. ToRscH ELECTRON BEAM DEFLECTION CONTROL SYSTEM Filed Sept. 25, 1946 INVENTOR y (lla/kflbffk BY Mfg/Wow ATTORNEY Patented May 17, 1949 ELECTRON BEAM'DEFLECTIN CONTROL ""SYSTEM Charles lEdWard .1 Torsch, `Lancaster T0wnship,

l.LancastercCoalitie-Pa., assignor to Radio AGorporation-of. America, a corporation of .Delaware Application September 25, 1946, Serial No."`699`,`172

711Glaims. il

The' present invention' 5relatesfto 'television sysite'ms, and more' particularly e'relates .to vmeans-*for ldei'lecting the electronscann'ing beamr ofi'anfm- Aarge-reproclucinefy cathoderay tube, `as .Well-.as to meansvfor supplying relatively high potentials for applicationlto the cathoderay ztuber accelerating electrodes.

Horizontal, yor "line,1 ydeflection circuits of tele Vvision receivers frequently include one yfor, more power output tubes-'from "which energy ;is supplied to` a pairot'fcath'ode raydbeam .deflection coils through.. an'fout'put transformer. @In order to i reduce the 'high-frequency*- oscillations vwl'nch normally occur i following the-retrace `p'eriods'of thel cathodel raybeam, av suppressorfor" damper, tubeis customarily :connected.acrossfeither the primary or' secondary winding of J this vroutput transformer.

The lrelatively high potentials' which areneo'essary to provide for :theaccefleration .of thef'cathode 4ray beam.' are.usuallyYl obtained either. from :a separate RF (radio-frequency) powersupply unit; for .la .rectiiiedl =60` cycle Jvp'ower: supply unit, not ifdirect1y. :associated with. the deflectionr circuit, or 'else Ithey may beiy obtained .A by vutilizing the surges of voltage developedfacrossithe deflection vcircuit inductance z-duringA the '-.beam 4:snap-bank, or' retrace; l`4intervals' when'f no por-tion.` of thev imagel-is'beingf reproduced. Tof-insure that lthese voltage surges 'are oflsufiicient:amplitudeyzin cases whereithefllattertmthod isi employed, a step -up winding maylfbefiadded toitheoutputtransformer, the voltagepulses-fdevelopedxacross thisA winding being f're'ctiii'ed and :.'filtered prior toE fthei-r application -fto' the yelectrodes vfof ithe cathodefray tube.

While the use of an output transformer between fpower ltube y and"` deflection -icoils is advantageous inw-permitting `yokesveof various impedan'eesi .toifbe :".lproperly fmfatch'ed 'to'wa ypower 'tube havingy a? iixed internal lresista-nce, :nevertheless the 'relativelyi yhigh cost :for vsuch transformers v"is an importantzlfactor 1in-the production of -certain classes ot-.television freceiving vrunits. Furthermore, unless ',.rltheviicoupl'ingbetween fthev primary andsecondaryvwindings bf the Ytransformer A-is very tight/excessive -los-sest--re'sult'-andthe Q of the circuit is lowered.

,MItl has ibeen f'ioundfrthat avsystem such the above :cmay be l 'changedfinto' a so-,called directdrive.-arrangementftoeffect Affunity coupling' ibetween--powen:tubeianddeflectionv coils. A choke the impedance offwhichfvisfhighcompared-to .that of 2 thadcection coils sovarranged as-.to -permit adjustmentmof thefdirectr current component ofyoke-.current by-ffmeans of ieicentering poten-- 2 t-iometers. Furthermore, "the high-impedance 'endrof this chokezmay be connected tolthe ano-de of the high-Voltage''rectifiertube,y :thereby `'supplying an aceeleratingz potential for fthede'lectron scanning beam. vfNotf'only is 4ithecost .oflsuchwa choke considerably lower than: that otra-suitable 'two-winding transformer; butfxin: addition,;high

er circuit eiciency-mayfbe obtained; since'eouypling losses are n-otfa'factor.

Generally, more cathode ray tube anodeyolt'- age isorequired' than can' fbe vobtained 'with .Pathe rectifier' :anode i connected directly- 'to'fithelpower tube anode. To lmeet this requirement,:the` high impedance chokezis'zherein Yshown a'portion of an autotransformer whiclrlsteps-upathei surge voltage (appearing 1 duringrretrace iat' '.thertpower tube anode) to axhigherr-peak voltage -atthe lrectier anode.

The core of theautotran'sformer whichforms part of the present-.inventionrequires at most but one section, or leegoand,` in addition, may have its physical dimensions held rto a` minimum. In' fact, it'has .been-found thatlinf-certaininstances the core 'elementlmayi-be Aomitted altogether with benecial'resiilts,since such an rexpedient reduces? the Yuxf 'transfer Abetween the ends of the choke winding and helps tovmaintain constant the plate *voltage-ofl the power output tube.

When no core is employed,- relatively 'large oscillations and other'dstortion ofthe waveform of the power tube output-'voltage will 'appear' at the high-impedance endof the choke, or,'in other words, at that end-of thech'oke vconnected `to the anode of the high-voltagefrectier tube. lWith a lter condenser'of proper Acapacitance in `series with the rectifier tube; however,y these'variations will have no appreciable e'iect'on fthe stability of the cathode ray tube anode voltage. Furthermore, from an operatingstandpoint, there is no necessity for the-waveform of the voltagev applied to the high-voltage'reotiiier tube to be similar to the waveform'of Athe Voltage outputof the power tube, as long as 'the peak'amplitude of the lformer `is suflicient to provide for the acceleration of theelectron scanning beam. Due 'to the loose coupling' between the coilportions, moreover, any voltage waveform distortion at the high-'impedancefend ofthe yautotransformer Will not feed back into 'the deflection circuit, .and hence will not adverselyaiect vthe linearity fof scan.

.Anadditional windingmay -be coupled l.niagnetically to .the autotransformer4 windings fonsupplying heater potential to the high voltage rectier.

A deection and power supply system in accordance with the present invention, or, in other words, a direct-drive system utilizing choke coupling, results in a high Voltage being developed across the line deection coils during retrace. This requires a yoke having higher impedance 1ine" deflection coils than commonly used, and is readily obtained by reducing the size of the wire employed in winding the yoke and by increasing the number of turns. With coil winding apparatus now in use, however, the diierence in cost between a yoke of the latter type and one of standard low impedance is not appreciable. Also, certain inherent advantages reside in the use of high-impedance yokes, among these being lower eddy current losses within the copper of the coil winding.

One object of the invention, therefore, is to provide a bridging element for cathode ray beam deflection circuits of the direct-drive type, this bridging element acting to provide accelerating potentials for the cathode ray beam, as well as to permit centering current adjustment in the yoke circuit. The high voltage rectier tube portion of the circuit may have its heater voltage supplied by an auxiliary winding magnetically coupled to the bridging element here tmentioned.

A further object of the invention is to provide a coupling or bridging element for cathode ray beam deection and high-voltage circuits which is simple in construction and relatively inexpensive to manufacture.

Other objects and advantages will be apparent from the following description of a preferred form of the invention and from the drawing, the single figure of which is a cathode ray beam deflection and high voltage circuit in accordance with the present invention.

Referring now to the drawings, there is illustrated a circuit for deecting the electron beam which is developed within a cathode ray tube (not shown) at horizontal, or line-scanning, frequency. This circuit includes a horizontal power output tube I having at least an anode, a cathode, a control electrode, and a screen electrode. The po-wer output tube IEI (such as a tube of the 807 type, for instance) is adapted to provide, when voltage variations which maybe such as indicated in the drawing by the reference character I2 are applied to the control electrode thereof, a current output of substantially sawtocth con- :guration to a pair of horizontal deflection coils I4 connected eifectively in shunt with a high-impedance choke, or autotransformer, I6.

The horizontal deflection coils III, in combination with a pair of vertical, or field, deflection coils, preferably form part of a yoke assembly encircling the neck of the cathode ray tube (not shown) to the second anode of which an accelerating potential is supplied over the conductor IB.

Across the horizontal deection coils I4 is connected the series combination of a damper tube 2U and a parallel resistance- condenser network 22, 24, the function of these elements being to damp out high-frequency oscillations which are produced in the deflection circuit following the retrace, or snap-back, portion of each deflection cycle.

In order that linear deflection may be produced, it is necessary that the rate of change of the current in the deection coils Ill be maintained substantially constant during the deflection cycle.

4 The action of the damper tube 2U is such that the current flow therethrough supplements the plate current output of the power tube II) to bring about a current flow through the horizontal deflection coils I4 which varies linearly with time.

The voltage variations applied to the control electrode of the damper tube 2B, and the normal bias of this control electrode must, therefore, be so adjusted as to give the desired waveform to the anode current permitted to ow through the damper tube. The means for obtaining such a voltage variation includes a differentiating network comprising a condenser 25 and resistors 26, 28, Iand 30, the lower plate (in the drawing) of condenser 25 being connected to the anode of thc damper tube 20. Bias for the control electrodo of damper tube 20 is obtained by means of the grid current flow through the parallel resistor- condenser combination 30, 32, one end of resistor 39 being connected to the cathode of damper tube 2D, as illustrated. Adjustment of resistor 28 varies the waveform of the voltage on the control electrode of the damper tube, and hence this element acts as a linearity control. Adjustment of rheostat 22 in shunt with capacitor 24 is a further control of linearity of beam deflection.

The anode of power output tube I0 is connected to a tap 34 on the choke I6. This tap 34 is also joined, by means of the conductor 36, to the upper end (in the drawing) of the horizontal deflection coils I4. The lower end of the horizontal deflection coils I4 is connected through blocking condenser 38 to the anode of the damper tube 2U, and also to the low-impedance end of the choke I6 by means of the conductor 4U. Thus, as far as alternating-current components in the deflection circuit are concerned, the lower portion of the choke coil I6 is effectively connected in parallel relation with the deection coils III, and also with the series combination of damper tube 20 and parallel resistance- condenser combina tion 22, 24.

In the arrangement illustrated, the cathode of the damper tube 20 (such, for instance, as a type GAST-G tube) is operated at high potential. Hence, in order to provide for proper operation of the system, the heater or filament of the damper tube 2|) is supplied with energy through a lament isolating transformer 42 constructed with low capacitance between primary and secondary windings as well as high voltage insulation between windings. In cases where the damper tube 2Il is designed with suitable insulating characteristics between its cathode and heater, however, the isolation transformer 42 may be omitted.

The upper portion of the choke I6 acts in effect as a transformer step-up winding, and is indicated in the drawing by the reference numeral 44. The upper, or high-impedance, end of this stepup winding 44 is connected to the anode of a high-voltage rectifier tube 46, which, by way of example, is a type 8016 tube. The filament of the rectier tube 4B is connected to ground through the filter condenser 4B, this lament being supplied with lament heating current from a lament winding on the choke I6.

Since the anode of the power output tube I0 is directly connected by means including the conductor 3B to the high-impedance end of the hori zontal or line deflection coils I4, it will be appreciated that the waveform of the lanode voltage deection coils.

imitatie??? them being applied overy the-.conductor I8 tof. the`Y 1o secondanodeeof'l the cathodef ray-image produce. ingntuber; I'fdlesired, an voltage dividerarrangef men-tr (not: .'shown),v may be.use;d-to..v obtain flowery voltages; for thezfotherelectrodesrof cathode.:

rayyltube, as welle esioc-focussingpurposes; Since-,L` 1*" GardenerL 25.=,1.o.o.mt.,

there; f isvery loose. coupling: between thehig-lr-y impedance. endof thev step-up7 windingf- Maudit-hef remaindemof the-autotransiormer I6.; the-.voltage.Y ons. the fuppen end offwinding 44. may have awaveform, whichois; at. variance with'the.v waveformsoi-`=5l the voltage appearing on theanodeeoi:the'powenvtube 10;; this"varian-ce.s beingduey primarily to an oscillation; oit-ringing of winding; 44.. Hout ever; it' ythe-'filter capacitor 4ta-is of, proper'l value@ these iluctuations': will notrappreeiablyf. affect, the. regulation of# ther D;r-C.;. output.. available.4 from.;A conductor lf8';; Obviouslys it'iu-rtheriltering;y is.: required, additionallgiiflter components; of known f. character may be added to the system illustratada.Y

Centeringfofthe catltioderaybeam is achieved by the use of two resistors 52 and 54 connected in parallel relation `as shown. The joined ends of these resistors 52 and,5.4,are respectively con.- nected to two sources of positives potential, repre--` sented in the drawing as +B1 and -l-Be. In practice, the value1 of the source ofv potential +B2 was chosento. be approximately 10.volts higher than theyalueof the source of potential-l-Br, although obviously this difference d'ependsinA part upon .the values of' the remaining components of the circuit.

Resistor 52 is provided with an adjustable tap 56 which is connected to the anode of damper tube 20. Resistor 54 is provided with an adjustable tap 56 which is -connected to the low-impedance end of the horizontal deflection coils I4. In other words, these two taps 56 and 58 are separated electrically by the blocking condenser 38.

Taps 56 and 58 are intended to be ganged, as shown by the broken lines in the drawing, so that a movement, say, of tap -58 to the right (or toward a higher voltage value), will result in a corresponding movement of tap 56 to the left, or, in other words, toward a lower voltage Value. The 5, difference in voltage thus established between taps 56 and 58 causes current to flow from tap 58 through the horizontal deection coils I4, conductor 36, the lower portion of choke I6, partially through tube when conducting, and conductor to tap 56, this current flow through the horizontal deflection coils I4'eiecting a centering of the cathode ray beam in a known manner.

It should be noted that the screen electrode of power output tube l0 is connected to tap 56 65 through the conductor 40, and thus is provided with a suitable operating potential from this source. The screen electrode of power output tube I0 may, however, be operated at a lower or adjustable potential.

The following tube types and component values have been found suitable in practice for obtaining the results stated herein. However, it is to be clearly understood that these tube types and component values are being given merely as exanuales;l and' that'. substitutions: may be.y made# therefor as. found convenient yor.desirable:.l

Rectifier tube.46-:Typell33fGT/8Q16. Damper tubefZllT-Ty-peGAS'I-.Ct

-l-Bz--Sdu volts.

Resistors .52 and54=100 ohms. each Capacitor V3.8.,:1 mi.

Resiston 22:50.00. ohms,

Resistor.. 3.0 =10.0,Q00, ohms` Capacitor. 32;:.02 mf...

Resistor 26,==.510000. ohms- Capacitor. 24: 4. mi. l

Inductanee.. of deectipn. .coils I 4.2 l0. milllihenries, for single-.'GBGGG? (Proportionatelyllowerfin l ductance. is :desirable when additional, 6BG are paralleled withtheoriginal.4 outputtube, a single tube of higherplate. currentgrati-ngff s: substitutedf) circuit rof:4 said power youtput tube; means f orcon-' necting one terminal` oif'said-pairsotcathode ray-2 beam d'eecti'on-f coils to the said intermediate point-on.A saidiautotransiormerwinding; a` source oi'fanode-potentialifor the,r said lpower output tuberi connected to. the remaining terminal ofi said'pailir@` of cathode ray beam deection coils; and a source of screen potential for the said power output tube connected both to the said screen electrode and to that end of the said autotransformer winding which lies in the said power output tube anode-cathode circuit, said source of anode potential being of a different value than said source of screen potential, whereby a centering current for the said cathode ray beam representative of the difference between the Values of the said two sources of power output tube potential lwill ow through the said cathode ray beam deection coils and also through that portion of the said autotransformer winding which lies in the anode-cathode circuit of said power output tube.

2. In a cathode ray beam deection and highvoltage system: a pair of cathode ray beam deflection coils; a power output tube including at least an anode, a cathode, and a screen electrode; an autotransformer; means for connecting the anode of said power output tube to a point on said autotransformer winding intermediate the ends thereof, so that a portion of said autotransformer winding lies in the anode-cathode circuit of said power output tube; means for connecting one terminal of said pair of cathode ray beam deflection coils to the said intermediate point on said autotransformer winding; a source of anode potential for the said power output tube connected to the remaining terminal of said pair of cathode ray beam deection coils; a source of screen potential for the said power output tube i connected both to the said screen electrode and to that end of the said autotransformer winding which lies in the said power output tube anodecathode circuit, said source of anode potential being of a different value than said source of screen potential, whereby a centering current for the said cathode ray .beam representative of the difference between the values of the said two sources of power output tube potential will ow through the said cathode ray beam deflection coils and also through that portion of the said autotransformer winding which lies in the anode-cathode circuit of the said power output tube; and means for rectifying and filtering the voltage developed across the entire winding of said autotransformer so as to obtain therefrom a substantially smooth cathode ray beam accelerating potential.

3. A cathode ray beam deection and highvoltage system according to claim 2, in which said rectifying and filtering means includes an electron discharge device having a heater element, an auxiliary winding on said autotransformer, and means connecting said heater element to said auxiliary winding.

4. In a cathode ray beam deflection circuit, a power output tube including at least an anode and a cathode and adapted to deliver a cyclically varying current output, an autotransformer having a portion of its winding connected in the anode-cathode circuit of said power output tube, a pair of cathode ray beam deection coils connected eiectively in shunt with the said portion i of said autotransformer winding, a source of anode potential for the said power output tube connected in series with said pair of cathode ray beam deflection coils and means including a rectifier for deriving a direct voltage from the entire winding of said auto-transformer.

5. A cathode ray beam deflection circuit in accordance with claim 4, and wherein said rectifier has an anode electrode and a cathode electrode, one of said electrodes connected to the opposite end of said autotransformer winding from that included in the anode-cathode circuit of said power output tube and a direct voltage output terminal connected to the other of said electrodes.

6. In a cathode ray beam deection circuit, a power tube having at least an anode, a cathode and a screen electrode, and adapted to deliver a cyclically varying current output, an autotransformer having a portioniof its winding connected in the anode-cathode circuit of said power tube. a pair of cathode ray beam deflection coils connected effectively in shunt with the said portion of said autotransformer winding, a source of anode potential for said power tube connected in series with said pair of cathode ray beam de ection coils, and a source of screen potential for said power tube connected both of said screen electrode and to that end of the said autotransformer winding lying in the said power tube anode-cathode circuit,

7. A cathode ray beam deflection circuit in accordance with claim 6, in which said source of anode potential is of a different value than said source of screen potential, whereby a substantially constant current representative of the difu ference in value of said potential sources will flow through said pair of cathode ray beam deflection coils.

CHARLES EDWARD TORSCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATESy PATENTS Number Name Date 2,074,495 Vance Mar. 23, 1937 2,280,990 White Apr. 28, 1942

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