US2570017A - Television receiver chassis construction - Google Patents

Description

Oct. 2, 1951 F. L. WEDIG 2,570,017

TELEVISION RECEIVER cHAssIs CONSTRUCTION Filed Nov. 2, 1949 2 Sheets-Sheet 1 IN V EN TOR. FRANK L. WED/G Oct. 2, 1951 F. L. WEDIG 2,570,017

TELEVISION RECEIVER CHASSIS CONSTRUCTION Filed Nov. 2, 1949 2 Sheet s-Sheet 2 SIGNAL INPUT IN VEN TOR. FRANK L. WED/6 Patented Oct. 2, 1951 TELE ON RECEIVE HASSIS. CONSTRUCTION Frank L. Wedig; Cincinnati, Ohio, assignor to Avco. Manufacturing; Corporation, Cincinnati, Ohio, a. corporation of Delaware;

Application November 2, 19/49, Serial No, 125,071

The present invention relates to an improved chassis construction for direct-power-line-connected (power-transformerless) type television receivers. The primary object of the present invention is to provide such a chassis construction that a common metallic element for supporting the various receiver components may be maintained at a substantial potential difference with respect to true ground without presenting a shock hazard to the user or operator and without requiring the individual insulation of manually operative control shafts and special precautions forindividually insulating the main chassis mountings from the cabinet.

Alternately stated, the primary object of the invention is to provide a simple construction for insulating the manually operative controls from "a hot common metallic support for the various receiver components, this support being directly connected to one side of the power line.

Another basic object of the invention is to provide a chassis construction whichcan be directly mounted in a wooden cabinet without the taking of special precautions to insulate the bottom of the metallic chassis from the wood.

Still another object of the invention is to provide a chassis construction in which the main chassis body is cold, i. e., at true ground potential so that it can function as part of the exterior of the receiver, in conjunction with a subchassis so arranged that the construction provides the lowest possible impedance in RF returns, such as those between the various tuned circuits and ground. In the interests of receiver efliciency and stability it is desirable that there be provided a low impedance path between the vacuum tube circuits and the common base plate, at least for radio frequencies. An object of this "invention is to make that impedance as low as possible, because high common impedances in these circuits result in undesired stray couplings.

In the usual receiver installations one side of J the supply line is connected to ground and it is impossible to connect one side of the conventional chassis construction to ground, when an unpalarized powerplug is employed, because of the existence of the hazard of a direct short circuit across the supply line. This means that the usual one-piece metallic chassis construction may be hot and at a high potential difference with respect to true ground when the tube cathodes and power supply lines are directly connected to the chassis, for example. In or- 1 derto prevent this potential difference from con 2 Claimsi L. 250-16,).

2 V stituting a shock hazard to the user of the. receiver, it is necessary to insulate the, mannually operative parts or shafts of the various controls from the conventional hot chassis, also to insulate the metallic supporting mountings at the bottom of the chassis construction from the wooden cabinet, since underwriters" requiree ments do not permit a hot chassis to be mount..- ed directly on wood, the latter being regarded as a poor insulator.

When it is considered that a television receiver generally includes a large number of controls such as the contrast control, the brilliancy control, the volume control, the horizontal frequency control, the horizontal lock control, and so forth, it becomes apparent that the individual isolation of the manually operative shafts of the various controls from a hot chassis presents a very costly engineering and construction job. The cost and difliculties involved are considerably aggravated when it is borne in mind that the lower mountings which are employed to support the conventional chassis must also be individually specially insulated from a wood cabinet, since no hot metallic elements are permitted directly to contact such a receiver cabinet.

The chassis construction provided in accordance with the, invention consists briefly of a common metallic plate which is connected to one side of the power line to provide an electrical ground or chassis ground for the various receiver components. To this plate are connected all of the circuit elements requiring a common or chassis ground. This plate is mounted atop a box-like main chassis or tray and the plate is insulated from the main chassis member or tray by a plurality of insulating supports. The common plate may be "hotwhile the main chassis tray is cold. The chassis tray therefore presents no shock hazard to the user and the users controls which project forwardly from and through the tray do not have to be insulated therefrom. The very simple and inexpensive insulating means between the top plate and tray is provided in lieu of the large number of complex individual insulating expedients heretofore employed with respect to each control and each mounting between chassis and cabinet. For a better understanding of the present invention, together with other and iurther o jects, advanta s, and p i it es th re refe en is mad to the accom any n drawings. in which there, is shown an il ustrative pre er-re form of chassis construction in accordance with the invention.

In the drawings:

Fig. 1 is a front perspective view of a television receiver having a chassis construction in accordance with the invention;

Fig. 2 is a fragmentary elevational sectional view taken along the line 22, looking in the direction of the arrows; and

Fig. 3 is a circuit schematic showing the connections of the power supply and other illustrative receiver components employed with a chassis construction in accordance with the invention.

Referring now specifically to Fig. 3 of the drawings, the novel chassis construction in accordance with the invention comprises a metallic chassis tray II, the front wall 12 Of which is shown in section, and a metallic top plate or lid l3, shown in section, suitably insulated from the tray. The tray is flanged inwardly at the top, as indicated at Hill.

The supply mains l4, [5, one of which is connected to true ground at l6, terminate at socket l8, which receives the contact prongs of a conventional plug H3, at the end of supply conductors 20, 2|. Conductor 2| is directly connected to the metallic top plate l3. Conductor 28 is in series with a resistor 22 and rectifier 23. The power supply is completed by a series choke 24 and a pair of shunt filter capacitors 25, 26. The power supply output terminals are shown at 28 (+13) and 2! (B), the latter being shown at the point of connection of supply line conductor 2| and top plate [3. It will be understood that the whole of plate I3 constitutes a chassis ground for the various circuit components. This plate, as indicated, is directly connected to one side (2|) of the power line.

As shown in Fig. 1, the various television receiver components are mounted on plate l3. In the specific illustrative example shown, these components may comprise:

Cathode ray tube 30 Loud speaker 3| Deflection yoke 32 Focus coil 33 Horizontal output transformer 34 Synchronizing signal separator tube 35 Synchronizing signal amplifier tube 36 Video detector tube 31 Video amplifier tube 38 First, second, third, and fourth intermediate frequency amplifier tubes 39, 48, 4|, and 42 Horizontal damper tube 43 Horizontal oscillator and control tube 44 Blocking oscillator transformer 45 Audio power output tube 46 Electrolytic capacitor 48 Audio amplifier tube 49 Radio detector windings 50 Vertical oscillator and output tube Radio detector tube 52 Horizontal driver tube 53 The R. F. amplifier tube 54, mixer tube 55, and oscillator tube 56 are supported on a metallic bracket 51, secured within an opening 58 on plate l3.

The specific arrangement of the components supported by plate l3, as herein described, is exemplary and the invention is not limited to the particular arrangement illustrated in Fig. 1.

Referring again to Fig. 3, there is shown a portion of the signal channel of a typical intercarrier-sound type of receiver utilizing the invention.

This channel comprises a fourth I. F. amplifier stage including a tube 42. The signal input circuit of this tube is tuned by a circuit comprising an adjustable iron core inductance 6|, tuned by its own distributed capacitance and shunted by a damping resistor 63, this tuned grid circuit being returned to top plate 13, which provides a common ground. The anode of tube 42 is connected to a plate load inductance 64. The junction of the screen grid and plate load is connected to high potential terminal 28 of the power supply. The cathode is connected to top plate [3, through a bias resistor H, by-passed by capacitor 12.

The output circuit of tube 42 is coupledtoavideo detector tube 31 by a capacitor 55. The detector circuit network includes peaking inductors 85, 81, capacitors '68, 68, and resistor 10, this detector network being essentially the same as that disclosed in the copending patent application of Francis A. Wissel and Norman W. Parker, entitled Automatic Gain Control, Serial No. 102,176, filed in the U. S. Patent Office on June 30, 1949, and assigned to the same assignee as the present application and invention.

The detector output circuit is coupled by a series peaking inductor 13 to the input circuit of a video amplifier tube 38. Contrast is varied by short-circuiting various portions of cathode resistor 14 by an adjustable contact 15, connected to top plate [3. The cathode of tube 38 is returned to the common ground provided by top plate l3. The anode of tube 38 is connected to a parallel combination of peaking coil 16 and damping resistor 11, which in turn is connected to a resonant circuit comprising inductance 18 and capacitor 19. The anode of tube 38 is connected to the high-potential terminal 28 of the power supply through the D. C. path provided by inductors l6 and I8, shunt peaking inductor 88 and load resistor 8i. The sound signals are taken off by a circuit (not shown) inductively coupled to winding 18. The showing of tubes 42, 31, and 38 is made for the purpose of showing typical methods by which cathodes and tuned circuits may be returned to the common ground provided by top plate l3, thereby minimizing undesired couplings between, and stray disturbances aifecting, the various tube circuits. It is to be particularly noted that the invention accomplishes this advantage without presenting a shock hazard to the operator.

Resistor l4 and sliding contact 15 are symbolically shown in Fig. 3, in dotted outline, within the body of a standard control unit or rheostat 82. This unit has the usual metallic manual control shaft 83, which rotates within a journal 84 provided by a metallic boss projecting from the body of the rheostat. The rheostat is of any suitable conventional construction such that the resistor 14 and contact 15, or equivalents, are insulated from the exterior of body 85 and brought out to terminal lugs 86, 81, and 88.

The boss 84 and shaft 83 project through an opening in the front wall 12 of chassis tray ll, so that the contrast control 14, I5 is located in its customary position, readily available to the operator, in fact in the position which has become standard in television receivers. This is accomplished without taking any special precautions whatever for insulating shaft 83 and boss 84 from the metallic flange I2. Heretofore, in the manufacture of television receivers, it has been necessary to take particular precautions to insulate such bosses and shafts or equivalents from the front flange of the chassis, in order to prevent the existence of a shock hazard to the user. This shock hazard existed whenever the front flange is hot or may become hot. The construction in accordance with the present invention insures that this front flange will be cold at all. times.

In accordance with the invention the top plate I3 is mounted on and insulated from the chassis tray I I by a plurality of mountings such as those illustrated at 90, 9|, 92, and 93 in Fig. 1. Mounting 9| is illustrated in detail in Fig. 2. The main chassis tray II is flanged inwardly at the top as indicated at I and is suitably apertured and threaded to receive the shank IllI of a bolt I02. The head of this bolt reposes on the top flange I 03 of a metallic bushing I04. Bolt I02 and bushing I 04 are maintained in cold condition by an insulating washer I05 which is formed with an annular groove I06. Top plate I3 is suitably apertured to define an annular shoulder I 01 which is received within groove I06. Washer IDS is made of rubber or suitable flexible insulation which may be deformed and manually pressed into place. Washer I05 performs the function of electrically isolating top plate I3 from chassis tra I I. It will be understood that the mountings 90, 9|, 92, and 93 are of substantially similar construction and that other suitable mountings which isolate top plate I3 from chassis tray I I may be employed within the spirit and scope of the appended claims. Thus it will be seen that the invention provides such a chassis construction that the common metallic element I3 for supporting the various receiver components (such as those illustrated in Fig. 1) may be maintained hot or at a substantial potential difference with respect to true ground (1. e., the potential level of the operator) without presenting a shock hazard to the operator and without requiring the individual insulation of manually operative control shafts such as shaft 83 in Fig. 2. Additionally, this chassis construction requires no special precautions for insulating the bottom of the tray I I from a wooden cabinet, for example. Further, the tray I I can function as a part of the exterior of the receiver, minimizing the expense of cabinetry. When it is considered that television receivers comprise a, large number of controls (of which the contrast control herein shown is simply representative), such as the contrast control, the brilliancy control, the volume control, the horizontal frequency control, the horizontal lock control, and so forth, it will be understood that very significant economies in engineering and manufacturing may be accomplished through the practice of the present invention.

While there has been shown and described what is considered to be the preferred embodiment of the present invention, it will be obvious to those skilled in the art that various modifications and substitutions of equivalents may be made therein without departing from the true scope of the invention as defined by the appended claims.

I claim: I

1. A chassis construction for a television receiver, of the type which includes radio frequency selector, frequency-changing, and amplifier circuits, which receiver is energized from two-conductor mains, one of which may be at the potential level of the operator, and which receiver includes contrast and other control units having metallic control shafts, comprising: a metallic box-like tray, formed with an open top and individual apertures, for providing a mechanical support for the manually operated shafts and outwardly projecting metal parts of said control units, said shafts projecting through said apertures, a metallic top plate which substantially closes said tray and provides a support for said circuits, means for mounting said circuits, and means comprising a plurality of insulating spacers securing said top plate to and electrically insulating it from said tray for the purpose of preventing the connection of one of said mains or an equivalent potential point to said top plate from creating a potential difference between said tray and the operator, whereby said shafts and said metal parts do not present any shock hazard to the operator and may directly contact sa1d tray, and means for connecting one of said mains to said top plate.

2. A chassis construction Ior a television receiver of the type which is energized from twoconductor mains and which includes control units having projecting manually operated metal shafts, comprising a metallic box-like tray, formed with an open top and individual apertures for providing a mechanical support for said shafts, said shafts projecting through said apertures, a metallic lid panel which substantially closes said tray, means comprising a plurality of insulating spacers securing said lid panel to and electrically isolating it from said tray for the purpose of preventing the connection of one of said mains or an equivalent potential point to said lid from creating a potential difference between said tray and the operator, whereby said tray does not present any shock hazard to the operator, and means for connecting said one of said mains to said lid panel.

FRANK L. WEDIG.

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

UNITED STATES PATENTS Number Name Date 2,087,073 Smith July 13, 1937 2,443,449 Fry June 15, 1948 2,458,365 Fyler Jan. 4, 1949 FOREIGN PATENTS Number Country Date 414,819 Great Britain Aug. 15 1934 457,723 Great Britain Dec. 4, 1936

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