US2474988A - Method of manufacturing electrical network circuits - Google Patents

Description

METHOD OF MANUFACTURING ELECTRICAL NETWORK CIRCUITS Filed Aug. 16

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METHOD OF MANUFACTURING ELECTRICAL NETWORK CIRCUITS Filed Aug. 16, 1944.

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METHOD OF MANUFACTURING ELECTRICAL NETWORK CIRCUITS Filed Aug. 16, 1944 14 Sheets-Sheet 5 July 5, 1949. J. A. sARGRovE 2,474,988

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METHOD OF MANUFACTURING ELECTRICAL NETWORK CIRCUITS July 5, 1949. J. A. sARGRovE 2,474,988

METHOD OF MANUFACTURING ELECTRICAL NETWORK CIRCUITS Filed Aug. 16, 1944 14 Sheets-Sheet 10 F/G23A.,

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METHOD OF MANUFACTURING ELECTRICAL NETWORK CIRCUITS Filed Aug. 16, 1944 14 Sheets-Sheet l2 F/G33A.

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J. A. SARGROVE METHOD OF MANUFACTURING ELECTRICAL NETWORK CIRCUITS Filed Aug. 16. 1944 14 Sheets-Sheet 14 2/0 ZImwnmr;

Patented July 5, 1949 METHOD OF MANUFACTURING ELECTRICAL NETWORK CIRCUITS John Adolph Sargrove,

Shepperton-on-Thames, land Application August 16, 1944, Serial No. 549,770 In Great Britain August 30, 1943 Claims. (Cl. Ztl-155.5)

The invention relates to electrical apparatus and in particular to apparatus or instruments such as are used in -connection with telegraphic, telephonie, television reception and transmission and the like, in which a circuit system has to be arranged consisting of interrelated components such as resistive, capacitative and inductive circuit elements as well as ampliiier and reprodueing means such as valves, cathode-ray tubes, loudspeakers, and the like.

The invention is Ialso applicable to other electrical apparatus such as low current switch and instrument boards and the like.

The principal object of the invention is to provide an improved. and more economical method of manufacture.

The normal method of manufacturing electrical apparatus such, for example, as a radio receiver-for which my invention is specially applicable-is to mount the various individually made component elements on a supporting base or chassis-as it is usually calledand then connect them up in their proper mechanical relation by means of conductor wires soldered to the terminals of the various components.

It has, however, been suggested to provide insulating panels with conductor paths by electrodeposition, the conductor paths leading to, and being connected to. sockets into which specially made components such as transformers, condensers, resistors and the like provided with contact pins could be plugged in.

This proposal has not to my knowledge ever beencarried out in practice.

The present invention, which has already been carried out by me experimentally, differs from these prior proposals in that accordingl to my invention not only are Ithe conductor paths applied directly to the panel or chassis but components themselves of correct predetermined electrical values are applied to the panel or chassis and interrelated together with their conductor connections. It will, of course, be understood that such components as valves and loud speakers cannot be applied in this way but both the breadth and limitations of the'method comprising the invention will be made clear hereinafter, when the practical application of the invention to the construction of a radio receiving instrument is fully described. The invention can, however, be broadly stated as consisting of a method of manufacturing electrical apparatus consisting of interrelated component elements connected in circuit according to which electrical components or parts thereof of predetermined electrical `values and the conducting paths connecting the components in circuit are applied to and form integral parts of an insulating supporting panel.

It is to be noted that the term panel used herein is not to be regarded as limiting to flat constructions as the invention can be applied to curved surfaces and in particular to the walls of cabinets containing parts of the apparatus as will hereafter appear.

Moreover, the term insulating is not to be taken as implying that the panel is wholly of insulating material as in some cases conductive material may be incorporated in the body of the panel.

In order that the invention may be readily understood and'carried into practice reference is made to the accompanying diagrammatic drawings throughout which similar letters and numerals of reference are used for corresponding parts wherever occurring.

1n these drawings:

Figure 1 is a fragmentary plan view of a part of f a panel or chassis showing interrelated components and circuit elements or connections applied thereto in accordance with the general principles of the invention; and Figure 2 is a cross section thereof on the line X-X of Figure 1.

These two figures are solely for the purpose of a general description of the invention.

Figures 3 to 22 are for the purpose of explaining the manufacture of a complete two-valve radio receiver;

Figure 3 being a perspective view of one side of a panel moulded from insulating material upon which a two-valve all mains amplier is to -be built up in accordance with the invention;

Figure 4 is the same side of this panel after the grooves and indentations thereon have been i'llled with conducting material;

Figure 5 is the circuit diagram of the complete ampliiier but so drawn that only those parts in existence at the stage of production represented by -Figure 4 are shown in full lines. (The full thick lines showing the parts visible in Figure 4 whilst the fulldouble thin lines show the parts on the invisible side in Figure 4. The dotted lines are parts not yet present) Figure 6 shows the same side of this panel after resistors have been deposited, whilst Figure 7 shows the other side of this panel at -this stage of production;

Figure 8 is again the same circuit as Figure 5, but with many more parts shown in full lines, and represents the stage of production arrived at in Figures 6 and 7;

aavgoaa Figure 9 is the same as Figure 7, except that the eyelets, sockets and the like have been applied;

Figure 10 is the same as Figures 7 and 9 but with parts which cannot be made by this process such as valves, loud speakers and electrolytic condensers plugged into placecompleting the amplifier; g

Figure 11 is the circuit diagram (similar to Figures and 8) of the complete amplifier shown in Figure Y Figures 12 and 13 are perspective views of both sides of another moulded panel adapted to become the regenerative tuned circuit and associated aerial feed circuit of a radio receiver when it is combined with the Figure ,11 amplifier. (The panels shown in Figures 12 and'xl''have the same stage of the method of production as shown in Fig. 4)

Figure 14 shows the circuit of the above two figures; -1

Figure 15 is a fragmentary view of the panel in Figure 13 but afterrthe resistors have been depos- Figure 16 is the same panel with sockets, springs, variable condenser plates, assembly studs and the like inserted;

Figure 17 is the completed circuit of this panel shown in Figure 16;

Figure 18 shows a complete all mains (110 volt) broadcast receiver made in accordance with the invention by the continuation of the completed panels shown in Figure 10 and Figure 16:

Figure 19 is a view in perspective showing the interior of a moulded cabinet adapted to house the apparatus depicted in Figure 18 which has been processed in accordance with the inventions enabling the above broadcast receiver to function at various voltages up to 250 volts (it also shows part of the external mains connection attached thereto) Figure 20A is a fragmentary view of the underside of the cabinet (Figure 19) showing a tapping link provided to cut out various parts of the series resistor deposited inside the cabinet and thus adapt the broadcast receiver to the desired mains supply voltage;

Figure 20B depicts a similar fragmentary bottom view of an alternative cabinet arranged to have a mains switch included, which can be operated from the front of the receiver (shown here on top) Figure 20C is the inside fragmentary view of .e-:uch a cabinet showing two deposited conductor circuits both of which are adapted to be switched on or oi by the insertion of two metallic springs into lugs and a moulding insert;

Figures 20D, 20E and 20F show diagrammatically the action of such a switch in co-operation with the deposited conductors (shown black);

Figure 21 shows the circuit diagram of the electrical parts of such a cabinet made in accordance with the invention;

Figure 22 is the complete circuit of such a regional broadcast receiver made by the combinations of three basic parts, made in accordance with the invention shown in full black lines (the vertical dot-dash lines showing the conjointing place) which, with the iive parts (otherwise made) shown in dotted lines form the complete radio receiver (made up of the parts shown by Figures 11, 17 and 21);

Figure 23A shows in a plan view a method of designing part of a supersonic-heterodyne receiver.' the circuit diagram 0f this ment lle- 4 ing shown in Figure 23B. Figure 23A also shows a method of reducing leakage between adjacent deposits;

Figure 23C is a cross section of the above, showing also one method of transconnecting the circuit portions on either side of a panel with each other;

Figure 24 shows some of the alternative methods also in cross section:

Figure 25 is a cross sectional view of an example of reversing the sequence of production operations from first metallising and then graphitizing to the opposite;

Figure 26 shows a method of increasing the inductance of the coil in Figure 23C by making the Vplastic moulded 'panel from a substance having a'high permeability such as powdered iron core material; it also shows a manner in which the dielectric of a condenser from the same material can be improved;

Figure 27 shows an alternative to the previous one showing the powdered iron core material.

moulded into the normal panel, which has a keyed cavity preformed to takeit (theinterrelated metal deposits being applied in the normal manner into the communicating grooves) Figure 28 shows another alternative to the separation-of conducting and insulating parts of the panel, in this case the metal is deposited on to raised lportions as in the block printing technique, the deep lying part remaining unmetallised;

Figure 29A is a plan view of a further fragment of such a receiver and shows a method of designing a capacity coupled band pass illter with associated parts diagrammatically shown in Figure 29B, all of which are interrelated.

Figure 30A shows a plan view of an inductively coupled band pass circuit and associated parts, the circuit diagram of which is shown in Figure 30B;

Figure 31 shows in a cross sectional view an alternative method of coupling two inductors made in accordance with the invention;

Figure 32 is a cross sectional view of inductive elements, so produced and arranged as to enable the inductances to be varied, within small limits;

Figure 33A shows an example of a short wave band spread oscillator in a fragmentary plan view, part of the circuit diagram of which is shown in Figure 33B, which is adapted to operate on many wave bands;

Figure 34A shows a perspective view of a moulding made in accordance with the invention, adapted to form the rotor member of a double variable condenser;

Figure 34B shows a cross section of same;

Figure 34C shows in cross section a similar moulding with powdered iron core material moulded into the cavities for varying the inductance of two coils;

Figure 35A shows a perspective view of a moulding adapted to be the rotor of a variable condenser;

Figure 35B is a cross section of same;

Figure 36 shows a cross section of a moulded disc, one side of which is adapted for increasing the inductance oi' a coil and the other side for reducing it;

Figure 37A shows in fragmentary perspective view a method of increasing the inductivity of deposited coils by the insertion of conventional shaped powdered iron cores;

Figure 37B is a cross section of same;

Figure 37C is the plan view of an improved shape otpowderediron core for this purpose;

Figure 38 is a fragmentary plan view of a method of providing intimate coupling between the inductors ;v

Figure 39 is a perspective illustration of a method of assembling several plates made in accordance with the invention and by interrelating them with valves, cathode ray tubes, transformers and the like providing an economical method of manufacturing devices, such as oscilloscopes and television receivers;

Figure 40A shows a perspective view of a method of plugging a sub-panel made in accordance with the invention into another part of an electrical apparatus which may or may not necessarily be produced by the same method;

Figure 40B is a plan view of such a sub-panel; and

Figure 40C is a diagrammatic circuit of same;

Figure 41 is a fragmentary plan view of an alternative method of making connections to a valve from a deposited conductor network avoiding the need of sockets;

Figure 42 is a fragmentary plan view of a method, particularly suited for use with an electron-multiplier tube of making a resistance network and the conductor and tube contact parts in a very simple interrelated manner. The resistance material in this case can be squeezed into prepared keyed grooves in the moulding proccss akin to that depicted in Figure 27 for powdered iron core material.

Referring first to Figures 1 and 2, the panel a of insulating material has upon both side surfaces indentations of different depths such as b which when partly lled with metal (shown black and indicated by the reference m in Fig. 2) form one pole, or plate, of a condenser; and grooves, such as c filled with metal forming a conducting path or connection which under orthodox methods of manufacture would be a wire soldered at both ends` The hole d for fixing this panel mechanically to some other part of the apparatus e. g. the cabinet is surrounded by a circular groove filled with metal e1 which is interrelated with grooves similarly filled with metal such as e2, e and e3.

A typical interconnection from conductor paths e, e1, e2 and e3 on one side of the panel a to conductor paths on the other side such as f, is shown between metal deposit e2 with metal deposit f located on the nether side of the panel, the interconnection being provided in this case by an eyelet h pressedand riveted into a suitable hole.

Other conductor paths on the other side of the panel are groove i connecting point f and some other element not shown and shallow indentation g which lies directly opposite the above referred to deeper indentation b.

nation lobes at the ends of the deposited metal conducting paths. This is an operation easily mechanised and avoids the use of and consequent need for wiring up a separate valve holder.

Coil lis a high frequency choke coil the outside turn of which is directly interrelated with the conducting path e2, e3. The inside end communicates by way of an eyelet'connection with an enlarged 'lobe of conductingpath c and g in the other side of the panel a.

In a similar form to the interrelated deposited metal configurations on the main body of panel a, associated metal deposits can be arranged on a v movable circular panel inserted into a clearance hole such as the switch rotor disc o. In this case the deposit n forms a movable metallic link -between the switch contacts such as p which can be arranged around o at any convenient position.

It will be seen that the stationary switch contact blades, such as p are eyeleted right into the enlarged termination lobes of the deposited metal conducting paths. This is another operation easily mechanised and avoids the laborious switch wiring operation and also circumvents the need for careful inspection after wiring which is nor- 4 mally required to avoid wrong connections.

To ensure better contact for the switch the link deposit n can be reproduced on both sides of the rotor disc o and the stator contacts such as p can also be duplicated on both sides.

Having shown, by way of example, a wide rangeA of circuit components and conducting paths that can all be conveniently deposited of one kind of conducting material such as metal of high conductivity, e. g. copper, other circuit elements such as resistors can be, produced in situ such as r1 (shown with slant shading in both figures) by depositing, for instance, graphite` on to the surface of panel a in the space between the metal de-` Provided the specific density and thickness of the resultant deposit of graphite or other resistive material is accurately controlled the various resistance values required can be obtained by merely varying the aspect shape of the resistor deposit.

The latter two metallised indentations (y and b) form a fixed condenser the dielectric of which is of the same moulded plastic substance as a and is preformed at the same time as the whole panel, a thin web w (Fig. 2) being produced in the mould.

The preceding shows a typical case of a fixed condenser formed in situ already for use, completely interconnected to the circuit network and requiring no prefabrication and manual assembling, wiring and soldering operations to connect it into the circuit.

At y a hole is shown with the well known key way. This serves to locate a thermionic valve into the surrounding valve pin contact sockets such as lc. It will be seen that these valve pin contacts are eyeleted right into enlarged termi- (=100 milliwatts).

As an example, using a certain colloidal dispersion of graphite in a suitable slightly glutinous medium (such as gelatine) and deposited to a controlled thickness of say 1/20 millimetre one obtains a specific coating resistivity of 25 ohms per square millimetre area when measured from one edge to the parallel edge opposite. This small area is capable of continuously dissipating one milliwatt of energy in the form of heat without rising above a safe working temperature. A wide range of resistor values can be obtained by simply varying the shape and size of the deposit. A few instances will serve to illustrate this. A deposit area one mm. wide and mm. long lwill give in the above case a resistor of 2500 ohms. This will be able safely to dissipate le of a Watt Again a deposit 10 mm. wide and 10 mm. long will have a value of 25 ohms and dissipate 116 watt; another deposit 0.2 mm. wide and 100 mm. long would have a value ot 12.500 ohms at l/o watt; whereas a deposit 25 mm. wide and 40 mm. long would be 40 ohms at one watt.

Similarly other ranges of values can be obtained with similar shapes by varying the con` trolled thickness of deposit (i. e. varying the spraying time) or by changing the density of the deposit (i. e. by varying the dispersion of graphite in the medium) In large scale production several pistons can be used depositing various dispersions of graphite in sequence in each case a different stencil arrangement being employed so that the required sprayed deposit goes to the required place in the circuit.

In practice, one can easily obtain a range of values from 1 ohm to l0 megohms with three dit- Ierent dispersions. Wattages in the lower ohmic values can be up to 10 to 20 watts. This range of values is ample for radio receiver practice. It may be considered a disadvantage of this method that the higher wattage values ot resistors occupy more surface space than is the case with the prefabricated solid stick-like resistors. This is not necessarily a disadvantage as the heating up and continuous heat dissipation of these resistors is much more uniform and the reliability, constancy and endurance of resistors made in accordance with the invention is very high. It should be noted that the larger wattage resistors are according to this invention conveniently sprayed onto the surfaces of the cabinet walls, spreading out the heat radiating elements.

It should be noted that in these proposals the contacts to the two ends of the resistors is obtained without a separate operation by depositing the resistor right into its intended place in the circuit so that it overlaps the previously, or subsequently, deposited metal conductor path deposit over a suilicient area to achieve good contact. It is preferable so to shape the larger wattage resistors that the graphite deposit is widened near the contacts so that the temperature gradient at the vline of contact between hot graphite and cold metal is not too sudden.

To enable a very long and narrow resistor to occupy a relatively small surface area it can be conveniently deposited in a meander or zig-zag form. Such a resistor is shown at r4 (Fig. 1).

It is further convenient, in order to allow for 5 has only three turns and thus has only a very small inductance value coils of this construction can be made with many more turns of narrower surface width and closer spacing and also a total greater surface space area.

Obviously the maximum value of inductance that can thus be obtained has an upper limit which is lower than the conventional wire coils. Several methods of raising the maximum inductance value of coils made in accordance with the present proposals are shown in Figures 23 to 38 and will be more fully described hereafter. In general the kinds of inductances required for radio-frequency work of the order of approximately 1/2 megacycle to 100 megacycles can be arrived at by this means. Further, with certain modification of the described process involving the deposition of metal by known photo-chemical means either directly onto the main panel or onto a iilm and aillxing same. including photographically deposited interrelated conductor paths and condenser plates and the like, by a suitable adhesive, the connections being made between the nlm and the main panel where required by the circuit by means of eyelets or the like, greatly increased range of inductance values are obtainable.

There are certain limits to the values of condensers that can be formed in the manner shown in Figs. 1 and 2, and if larger capacitance values are required Athere can be obtained in accordance with these proposals as follows: The condenser can be produced in situ by depositing tlrst two metallic contacts one of which is as large as a condenser plate. This is sprayed over with a lacquer oi high dielectric coemcient, except the narrower metal contact and a narrow edge oi the luier plate, both o! which are masked. A iurthermnkisnowmedhavingalargecutout andenablingmetdtobesprayedthroughitso that it makes contact with the metal conductor of narrow dimensions. This toi-ms the second -plate ot the condenser. Now again lacquer is sprayed on with the same stencil as was used ior lacquer before. Then metal is again applied through the nrst metal spraying stencil; and so on until a stack is sprayed in which every alternate metal layer forms one pole of the condenser and vice versa. Of course three or more pole condensers can be similarly produced. Moreover, many condensers in many parts of the circuit can be similarly and simultaneously made in this multiplate form and also other interrelated parts or conductor paths can be sprayed on top of lacquer allowing ior instance a conductor path in between lacquer layers to cross over other conductor paths on the main panel as in between other lacquer layers.

A further alternative proposal of producing such interrelated condensers oi higher capacitance value is to make the whole main panel from a material of very high dielectric coemcient for instance by using a plastic illler of a substance with such a high dielectric constant, or by inserting a thin layer of such a substance with a roughened or etched surface into the mould so as to form the thin web w indicated in Fig. 2 when the plastic moulding is completed.

A further alternative is to make a sub-panel of a substance having a high dielectric constant on which part of the interrelated conductor paths and the high value condensers are deposited and this sub-panel is connected into the main circuit by eyelets and the like providing also the electrical connections between the circuits on the two panels. In general terms the upper limit of capacitance values that can be conveniently produced by these means lie in the region of 1000 micro-microfarads, using Bakelite panel material and up to 30,000 micro-microfarads (0.03 microfarad) with special materials such as suitable ceramic.

To obtain the greatest production economy the circuit design should preferably avoid the larger values of inductances and capacitances. (In many cases the required time constants of a part of a circuit can be obtained with smaller values of reactive components if the corresponding resistive component is increased.)

When larger reactive components are indispensable (such as electrolytic smoothing condensers) these can be preiabricated with plug shaped outlets and plugged into suitable sockets inserted into emerged lobes of the interrelated deposited metal circuit on the niain panel a.

Having explained the general principles of the.

invention reference is now made to Figs. 3-22 which illustrate the method oi production of a complete A. C./D. C. all mains 2 valve broadcast radio receiver, the complete circuit oi which is shown in Fig. 22.

Figure 3 is. as'before indicated, an isometric perspective view oi one side of a moulded plastic panel I of insulating material prior to deposition of any other materials. The arrow which appears on the narrow edge of the panel on this and several subsequent iigures serves to show which side of the panel is viewed and should be imagined as permanently inscribed on the panel.

Figure 4 shows the same side (see arrow) oi' the panel at a later stage in the production process after the moulding has been metallised all over in accordance with the invention by spraying the metal on from a pistol and thereafter face grinding the whole surface down with an abrasive in any known manner e. g. by a surface grinder so that only metal deposited in the grooves, holes and indentations remains on the panel.

Figure 5 shows diagrammatically the circuit scheme which this panel will ultimately carry.l It will be noted that this is the same electrically as the portion between the vertical dot-dash lines of completed receiver Fig. 22. However an unconventional mode of showing the circuit has been adopted in Fig. 5 (also in Fig. 8 and Fig. 14) to 4show the progress of the production sequence. In these three figures which all represent the identical circuit all those parts not yet present on the panel shown in the preceding iigure are shown with very thin dotted lines. These circuit components and conductor paths on top, i. e. visible, iny Figs. 3, 4 and 6 are shown with full black lines, Whilst those on the nether side in these gures but on top in Fig. '7 are shown as white lines, i. e. are thin double contour lines. The arrows in Fig. 6 and Fig. 7 serve to indicate which way up the panel is shown on the various figures.

Deep indentations 2a, 3a, la and 5a in the moulded panel i in Figs. 3 and 4 are intended after metallisation to form the top plates of each of the condensers shown with the same number in the circuit diagram, Fig. 5. To distinguish these deep indentations from through holes the shadow cast bythe walls of the indentations is shown on the webs of moulded plastic material at the bottoms of the indentations. These thin webs will form the dielectrict of these condensers. The reference characters from 6 to 30 on Fig. 3 are shallower indentations and grooves which will later serve as interconnecting conducting paths and termination lobes for sockets or eyelets. Their exact function will become clear to those versed in the art by comparison of Figs. 3 and 4 with Fig. 5. The number I which occurs several times in Figs. 3, 4, 6 and 7 relates to a large indeterminately shaped interconnecting metal deposit and its purpose is to act similarly to a grounding bus-bar of the metal chassis of a conventional receiver. It can be conveniently applied so that it is in continuous and intimate contact through the large round hole in the middle of the panel with another large interconnecting metal deposit on the other side of the panel. This is also marked 1 on Fig. 7. y

In most designs of a radio receiver it is good practice to make this element as all-embracing as possible and to be continuous with the grounded condenser plates as shown at 3a and 5a, in Fig. 4, andat lhinFlgs. 5. I anda.- A

f1'0 The various groups of smaller holes will be described later. The full' black and white lines in Figure 5 show how many separate assembly, fixing, wiring and soldering operations of the normal set making procedure have been eliminated by the simple and economical expedient of designing the panel moulding with recesses of the proper depth and coniiguration and comparatively more shallow grooves interconnecting the same, and by metallising this panel all over and grinding oir the surplus'metal from both sides so as to leave the metal only in the grooved and re- I cessed places.

Before explaining the parts in detail it will be noted that one of. the-reasons for the use of both sides of the panel is to allow the conductor paths to cross over each other, where required by the circuit. Another reason is to facilitate the arrangement of the fixed condensers in the circuit.

Figs. 6 and 7 show the application of the resistor elements. the resistors being shown as shaded areas; in this'instance one operation only is required for each side, the two sides being sprayed with a. diierent graphite dispersion, the specific resistance of the graphite deposit on the side oi the panel shown in Fig. 'I being approximately ten times higher than that shown in Fig. 6.

Viewing Fig. 8 and where necessary the preceding Figures. it will be seen that we have resistor 3i '(Fig. 6) of graphite deposited in a meander or zig-zag form between the lobes of metal conductors I9 and 20 to act as the anode load for the rst valve. Anothermeander form resistor 32 is inserted between conductors 20 and 23 to act as a. smoothing filter resistance. A straight narrow resistor with enlarged ends 33 is deposited between conductors 6 andll to act as a high-frequency stopper to assist regeneration in the aerial circuit which will be connected to point I8 (see Fig. 22).

A straight resistor 34 is deposited between conductor lobes 8 and 29 to act as a cathode-grid biasing resistance' for the second valve of the set.

A very small resistor 35 is deposited between the circular metal deposit 36, which will ultimately be the contact for holding one of the loudspeaker sockets 56 (see Figs. 9 and 10) and a similar circular metal deposit 31 which will ultimately be the contact holding the appropriate one of the valve socket eyelets 55. This resistor will act as an anti-parasitic oscillation anode stopper for the second valve. The very large resistor 38 is deposited between metal conductors i4 and l5, and acts as part of a heater-filament series resistance. This is a good example of a relatively large wattage resistor. Another large resistor 39 is deposited between metal conductors Il and [4 and acts as the other part oi the heater-filament series resistance.

It should be noted that the arrangement of splitting an electrical circuit componentin this case the heater-filament resistancehinto several separate parts,` either for the purpose of better utilisation of the available panel space or for any other purpose for instance spreading the heat radiating members to different regions of the panel or the cabinetv is easily'accomplished in accordance with this invention and furthermore this does not involve an increase in production costs. This constitutes a distinct advantage over more orthodox methods of production.

The resistor 40 deposited between metal conductors I0V and Il serves to limitthe charging surge current-ilowng 'out of the rectifier valve when-the receiveris-iirst switched on. for this purpose it has a comparatively large area and will stand very great overloads. Conductor ill also communicates with metal deposited condenser plate la, Figs. 4, and 6, which acts as a by-pass to grounding metal deposit 1 for parasitic high frequency oscillations generated by theA rectifier valve.

The meander form resistor 4i in Fig. 7 on the nether or under side of the panel (and consequently shown as double thin lines in Fig. 8) is deposited between the lobe 42 of the condenser plate 3b and conductor path 20 (Fig. 7) which transcommunicates by way of a small hole with conductor path 2li on the nether side (Fig. 6). This acts as a feed resistance for the screen grid of the first valve via the lobe I3 of the condenser formed by deposited plates 2a (Fig. 6) and 3b (Fig. 7), the latter acting as a high-frequency by-pass condenser for the same electrode. A very thin and long resistor M is deposited between the lobe 45 of the main grounding conductor deposit 1 and lobe I6 of the nether plate 2b of the audio-frequency coupling condenser composed of metal deposits 2a (Fig. 6) and 2b (Fig. 7). It will be noted that in the circuit shown in Fig. 8, the condenser plate 2b is in intimate direct contact with condenser plate 5b, the latter serving to produce a high-frequency by-pass for the control grid 'of the second valve. This direct intimate contact in this case is achieved as shown in Fig. '1 by making 2b and Ib into one individual peculiarly shaped metal deposit being in juxtaposition to the two separate deposits 2a and 5a on the former side of the plate (Fig. 6)

This facility of making high-frequency by-pass condensers in such intimate contact with the main (base) ground return is an advantageous feature which is not normally accomplished at such production economy. The very thin resistor 41 (Fig. 7) is deposited between lobe 4l of condenser plate 2b; 5b (Fig. 7) and circular metal deposit 49, the latter being the contact for the control-grid socket of the second valve.

An interesting feature of this system of producing a circuit arrangement is the facility enjoyed by the designer in screening certain sensitive points from picked up hum or unwanted leakage currents and like interference factors. A good example is shown here at 50 (Fig. '1) where a metal deposit going right to the side of the panel and attached to the socket of the cathode pin of the second valve (a relatively hum-free electrode), is used to screen the grid coupling condenser 2b of this same valve-a point very sensitive to external hum-from the influence by leakage or external radiation of the adjacent heater-filament contact pin, which is a point having a very intense hum voltage. Similarly on the other side of the panel the other plate 2a of this same condenser and its lobe i is screened from the humming points by the peculiar configuration of the main grounding electrode 1. This part of 1 is marked 9 on Fig, 6 and also at the same time acts as the means of interconnecting the grounding parts of this panel with the grounding parts of the other panel (see Fig. 18)

The point 5| (Fig. 7) is connected by way of metal path 52 to point 53. Path 52 has a high hum voltage hence it is run round outside the grounding electrode 1, sothat the latter screens it from acting upon sensitive points. Coming back to the resistor Il, which is the grid-leak of the second valve and hence also sensitive to hum, this is likewise arranged to be screened by nonhumming deposits 1 and Ib (see Fig. 7). Metal deposit 5I in Fig. 7 is an interconnecting path for cathode and suppressor grid and one heater pin of the first valve (see Fig. 8) as well as a grounding screen member shielding the hum-sensitive anode circuit of this same valve from humming point 5 I.

Considering Fig. 8 only we now see that except for items such as valves, electrolytic condensers and loud-speakers, we have made every component. Whilst this involved preparatory designing considerations, it requires only a few actual production questions which can be stated as follows:

l. Moulding the panel Fig. 3,

2. Metallising the same all over,

3. Grinding the surface of the panel to obtain the condition shown in Fig. 4,

. Spraying one graphite mixture through spaces on the surface of the panel shown in Fig. 6,

. Spraying another graphite mixture on the side of the panel shown in Fig. 7,

and fifteen electrical components all of individual character and electrical value and in their correct location and more than 35 conducting paths al1 in their correct location have connected these components in circuit.

We now require to provide for the prefabricated components to be plugged in. This is facilitated by inserting eyelets, sockets or the like as shown in Fig. 9. As these are in definitely prearranged positions automatic insertion of these small items and automatic eyeleting. riveting and the like becomes feasible.

Fig. 9 shows the same side of the panel as Fig. 7. At point 20 an eyelet is inserted through the panel to act as an interconnection from conductors on either side of the panel. At points marked 55 suitably shaped metal eyelet tags are inserted so that they radiate conveniently from which ever direction they happen to come into the valve pin socket holes arranged in a circle around key-way hole mentioned above to act in combination as the valve holders. All such tags are not numbered, though all are shown, and they are deliberately drawn in a slightly bent and irregular line to represent more clearly that 'they are springy parts attached on top of the moulding and not part of the latter. Sockets 5E for the two loud speaker connections are inserted into circular metal deposits 35 and 59 previously mentioned, shown in Figs. 6, 9 and 11. Specially shaped springy sockets 51 and 58, 60 and 6i are inserted into holes and cavities 2l, 24, 30 and I2 formed in the panel, which have been previously provided in the metal deposit paths (see Fig. 3) to act as sockets for the positive terminal plugs of electrolytic plug-in condensers. The individual function of each of these items becomes clear by comparing Fig. 11 with Figs. l0, 9, 8, 7 and 6.

It is preferable to spray the panel shown in Fig. 9 with lacquer to protect the deposited circuit, the relevant electrical connections and sockets being, of course, masked during the lacquering operation. This panel is now ready to have the prefabricated components plugged in as shown in Fig. 10. The valve marked 65 is the first valve previously mentioned and in this case is chosen to be of a type having its grid terminal 66 on top to facilitate its connection to the second panel to be described later, which carries the aerial input circuits.

The valve marked 61 is of the type containing an output system as well as a rectifier system. The loudspeaker 8l contains its own output transformer and in this example is of the perma-

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