US2438359A - Television receiver circuits and apparatus - Google Patents

Description

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March 23, 1948. R. G. CLAPP 2,438,359

TELEVISION RECEIVER CIRCUIT AND APPARATUS Filed Aug. 1, 1946 INVENTOR. R/(fi/IAD G. (ZAP? Patented Mar. 23, 1948 TELEVISION RECEIVER CIRCUITS AND APPARATUS Richard G. Clapp,

Haverford, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application August 1, 1946, Serial No. 687,639

The invention herein described and claimed relates to novel improvements in attenuators of t e type employing a plurality of variable inductance elements. More particularly the instant invention relates to improvements in picture size control apparatus such as is used in television receivers and the like.

In United States Patent No. 2,074,495, which issued on March 23, 1937 to A. W, Vance, there is described a cathode ray tube circuit in which the high, direct-current voltage required for the second anode of the cathode ray tube is derived from the horizontal deflecting signal circuit associated with the tube. This voltage is obtained by rectifying and filtering the very short, highvoltage pulses produced across the deflecting coils by the sudden collapse of the flux in the coil. A single one of these high-voltage pulses occurs once during each return line or flyback period.

In systems of the type described in the abovenamed patent, it is important, in practice, to ensure that necessary adjustments in picture widthi. e. in the magnitude of the sawtooth current flowing in the horizontal deflection coils-be effected by means which do not react back upon the sawtooth current source, since otherwise undesired, concomitant variations in second-anode potential will occur. In the past it has been customary to control picture width by means of 'a single variable-impedance element, but experience has shown that such devices are unsuited for use with cathode ray tube systems of the type hereinbefore described because of their effect on the second-anode voltage.

In accordance with the present invention there is provided a novel attenuator, or picture width control device, comprising a plurality of inductors jointly variable by means of a single moving element. This attenuator is so associated with the deflecting signal circuits, and its mode of inductance variation so chosen, that adjustments may be effected in picture size without producing deleterious changes in the magnitude of' the second-anode voltage.

Accordingly it is an object of the present invention to provide an improved and inexpensive attenuator suitable for use as a picture size control means in television receivers of the type which derive certain high operating-potentials from the receivers deflecting signal circuits.

It is another object of this invention to provide, in a television receiver of the type employing a deflecting circuit rectifier for the generation of high, direct-current potentials, a novel picture size control circuit, adjustment of which 2 Claims. (01. 315-27) 2 cannot deleteriously affect the operation or output of said rectifier.

These and other objects of the invention, and the manner in which they are attained, will appear from the following detailed description and the accompanying drawings, in which Fig, 1 is a schematic diagram of a preferred embodiment of the invention; and

Fig. 2 is a side elevational view, on an enlarged scale, of a physical embodiment of the attenuator device illustrated schematically in the circuit diagram of Fig. 1.

Referring now to Fig. 1, there is illustrated a portion of a television receiver-more particularly that portion which comprises the picture tube, the horizontal deflection circuits associated therewith, and the high voltage supply circuit for the second anode of the picture tube. Aside from the attenuator or picture width control device, which comprises the novel subject matter of the present invention, the apparatus illustrated in Fig. 1 is generally similar to that illustrated in the above-mentioned Vance patent, in which a detailed description of the modus operandi of the deflecting signal circuits andthe high voltage rectifier is to be found.

Briefly the system illustrated in Fig. 1 comprises a conventional cathode ray picture tube I having a cathode 2, signal grid 3, first anode 4, second anode 5, and fluorescent screen 6. Tube I may be provided with a pair of horizontal deflection coils I and a pair of vertical deflection coils (not shown). The sawtooth current Wave which is passed through the deflecting coils I is supplied by means of a circuit comprising the deflecting signal voltage source 8, deflecting signal amplifier 9, coupling transformer ID, the variable attenuator or picture-width control device I I, and the conductors I2 and I3.

High voltage for the second anode 5 of the cathode ray tube I is obtained from transformer II] by rectifying and filtering the high voltage pulses present thereacross during each return line or flyback period. The voltage available 1 across the primary of transformer In may be increased by the provision of an auxiliary winding I5, Together the windings I4 and I 5 function as an autotransformer to increase the magnitude of the pulse voltage available for rectification. The pulse voltage rectifier may comprise simply a diode l1, connected as shown, the rectified output current of the rectifier being filtered by any suitable filter network 21. The high voltage .pre'sent across the potentiometer 1815 applied to the second anode by way of the adjustable contactor l9 and the conductor 20.

As is well known in the art, it is necessary, in a television receiver, to provide an adjustable element by means of which the size of the raster, or scanning pattern, may be controlled or adjusted as occasion may demand. This is normally accomplished by varying the magnitude of the sawtooth current passing through the deflecting coils. In the past this has been done by varying, usually by means of a potentiometer, the magnitude of the deflecting signal voltage 8, or alternatively by shunting a variable inductance coil across the deflecting coils of the cathode ray tube In these prior arrangements the conductors l2 and I3 are connected directly to the extremities of the secondary winding it. However any variation in the magnitude of the voltage supplied by source 8 produces a like variation in the magnitude of the high voltage applied to the second anode 5. Similarly, any adjustment made in a simple shunt-connected inductor inevitably affects the magnitude of the second-anode potential because of the resultant change in transformer loading.

The objections inherent in the picture-width control devices of the prior art are eliminated by the improved control device of the present invention. This device is most conveniently regarded as an L-type attenuator comprising a series-connected variable inductor 2| and a shunt-connected variable inductor 22, the inductor 2| being connected in series between the secondary winding l6 of the transformer I0 and the deflecting coils I, while the shunt-connected winding 22 is connected directly in shunt with the deflecting coils. 1

As shown in Fig. 2 the windings comprising inductors 2| and 22 are assembled on a cylindrical coil form 23. The two windings are spaced apart sufiiciently to ensure that their mutual inductance is unimportant. One end of the coil form 23 is closed by a centrally-apertured internallythreaded disk 22. A single cylindrical core member 25, preferably composed of powdered or comminuted iron, and common to both windings, is axially movable within the coil form by means of a threaded adjusting screw 26. It will be observed that windings 2| and 22 are so positioned with respect to the limits of core travel that axial movement of the core member affects the inductance of the windings in opposite senses. Accordingly, referring to Fig. l, as the inductance of the shunt-inductor 22 is decreased (by movement of core member 25 to the left) the inductance of the series-inductor 2| is increased in such manner as to maintain the inductive load on the secondary winding I6 of transformer l0 substantially constant. In general the attenuator I should be so designed that, for any adjustment, the inductance of winding 2| plus the inductance ofthe parallel combination comprising windings i and 22, remains constant. Appropriate inductance values for windings 2| and 22 are easily arrived at by trial since the overall relations stated need be held over only the-relatively small range of adjustment normally required in practice.

When the attenuator device H is employed at very high frequencies, it may be expedient to construct the core member 25 of a non-magnetic material, such as brass or copper. If such a core material is employed, inductance variation is efiected as a result of magnetic field displacement rather than through an increase'in efiective permeability. Attention is also called to the fact that the core member need not necessarily move along the axis of windings 2| and 22 as shown in Fig. 2, but may instead be mounted exteriorly thereof in the manner suggested schematically in Fig. 1.

In one physical embodiment of the device of Fig. 2, which was constructed foruse with a television receiver having a 340 microhenry horizontal deflecting yoke, the coils 2| and 22 were mounted on a piece of dielectric tubing 21% inches long and inch in diameter. Coil 2| consisted of '70 turns of No. 28 SSE wire closely wound in three layers. Coil 22 was wound in two sections, or pies, each consisting of 180 turns of No. 7-41 SSE wire. The outside diameters of coils 2| and 22 were, respectively, A; inch and %'2 inch, their length being 11% inch and at inch respectively. The latter dimension includes a 3 2 inch spacing between sections. The spacing between adjacent ends of the coils 2| and 22 was inch. The length and. diameter of the iron core 25 measured "V8 inch and 1% inch respectively. The'ccre 25 was axially adjustable from the position shown in Fig. 2, in which it is spaced approximately /a inch from coil 22, to a position symmetricall centered with respect to coil 22. The permeability of the iron core 25 was such that the inductance of either of the coils is increased approximately three times by the insertion of the core. More specifically, as the adjustable core was moved from one end of its range to the other, the inductance of the series coil 2| increased from 37 to 122 microhenries while the inductance of the shunt coil 22 decreased from 3200 to 1020 microhenries. The inductance of the control unit, loaded with a 340 microhenry yoke, varied only from 355 to 350 microhenries (i. e. less than 1.5 percent) while producing a 20 percent change in picture-width. Throughout this range there was no detectable variation in either the potential of the high voltage supply or in the linearity of the horizontal sweep.

While the present invention has been described in combination with the horizontal deflecting signal circuits of a television receiver, it will be apparent that, alternatively, the device may be used in combination with vertical deflecting signal circuits. The attenuator is also useful generally wherever a simple, inexpensive inductance-type attenuator is desired.

I claim:

1. In a television receiver, a source of deflectin I signals, a cathode ray tube having a deflecting coil and a high voltage anode, means including said source for generating a high, direct-current potential, means for applying said potential to said anode, and an attenuator inserted between said source and said deflecting coil, said attenuator being constructed and arranged, in conjunction with said load, to maintain the effective load on said source fixed despite variations in the adjustnient of said attenuator, said attenuator comprising: a first inductance coil connected serially between said source and said deflecting coil, a second inductance coil connected in shunt with said deflecting coil, and an inductance-varying core member common to both of said inductance coils and movable with respect thereto, movement of said core member affecting the inductance of said coils in opposite senses.

2. The combination claimed in claim 1, characterized in that said inductance coils are sup ported in axially spaced relation on a hollow cylindrical coil support, said inductance-varying 5; member comprising a, ferromagnetic core axially movable within said coil support.

RICHARD G. CLAPP.

REFERENCES CITED 5 The following references are of record in the file of this patent:

UNITED STATES PATENTS N me Date 10 Number 6 Name Date Polydorofi Oct. 22, 1935 Vance Mar. 23, 1937 Crossley Dec. 5, 1939 Polydorolf Aug. 6, 1940 Holmes Dec. 3, 1940 Sands Sept. 9, 1941 Witthoft Aug. 4, 1942 Sharp Feb. 9, 1943 Stacker June 1, 1943 Warshaw Mar. 11, 1947

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