US2695963A - Fine tuner - Google Patents

Description

Nov. 30, 1954 E. P. THIAS 2,695,963

FINE TUNER Filed Dec. 125, 1951 8 Sheets-Sheet 1 l l 20 RM 12a foul/1v 511/; 7/14:

E. P. THIAS FINE TUNER Nov. 30,. 1954 8 Sheets-Sheet 2 Filed D80. 13, 1951 N MI IH E. P. THIAS FINE TUNER Nov. 30, 1954 8 Sheets-Sheet 3 Filed' Dec. 13, 1951 Nov. 30, 1954 E. P. THIAS 2,695,963

FINE TUNER Filed Dec. 13, 1951 8 Sheets-Sheet 4 a; k I 3 is A JJ: 5. E

I N VEN T98. Eoumv 5401. 0/46 BYMIYM Nov. 30, 1954 E. P. THIAS 2,695,963

FINE TUNER Filed Dec. 15, 1951 8 Sheets-Sheet 5 fan/m1 Array/V5 0 Nov. 30, 1954 E. P. THIAS 2,695,963

FINE TUNER Filed Dec. 13, 1951 a Sheets-Sheet e INVENTO ,Eaw/N f). #m:

BY Mad/("1% E. P. THIAS FINE TUNER Nov. 30, 1954 8 Shuts-Sheet 7 Filed Dec. 13 1951 INVENTOR. foa /w flu 79/4:

lrraen irs Nov. 30, 1954 E. P. THIAS 2,695,963

FINE TUNER Filed Dec. 13, 1951 8 Sheets-Sheet 8 I N V EN TOR. EDlll/N Pfll/L 77/14.:

wwn w United States Patent FINE TUNER Edwin Paul Thias, Los Angeles, Calif., assignor to Standard Coil Products Co. Inc., Los Angeles, Calif., a corporation of Illinois Application December 13, 1951, Serial No. 261,426

Claims. (Cl. 25040) This invention relates to television selectors of the type now known generally as television tuners and is directed more particularly to the arrangement of the fine or vernier tuning elements of the local oscillator structure.

In frequency selectors of the television tuner type, a step by step tuning arrangement is provided which is operated by a rotatable shaft to move successively a plurality of inductors into engagement with contact elements in order to tune the unit to the different television channels. As disclosed in prior applications 218,162, Patent No. 2,650,298, dated August 25, 1953, and 226,718, Patent No. 2,658,394, dated November 10,

a fine or vernier tuning arrangement is also pro- W e Various problems arise in fine tuners for television receivers due to the fact that the high channels from 7 through 13 operate at essentially three times the frequency of the low frequency channels 2 through 6.

Heretofore, in the prior art, the fine tuners of the conventional capacity type had a tuning range approximately three times as great on the high channels as on the low channels, due to the fact that as the frequency increases, the percentage change of frequency remains essentially constant so that the same angular rotation of the fine tuning shaft produces a greater absolute change in frequency. The fine tuning assemblies then tend towards rougher tuning on the high channels, covering a greater range of frequencies.

These difficulties are overcome by the provision of a fine tuning element having novel compact tuning assembly utilized cascade circuitry, having a simple driving mechanism, a printed base, printed coils, and inductive bucking effect which in combination with the capacitive variation provides substantially equal tuning ranges for the high and low channels.

It is then an important object of the present invention to provide a fine tuning assembly which has approximately the same tuning range on the high channels as it does on the low channels.

Another object of the present invention is the provision of a finer tuner having an inductive bucking effect so that two-thirds of the capacitive effect on the high channels is neutralized.

Still another important obiect of the present invention is to provide a novel fine tuning mechanism for television where the fine tuning may be initiated on a shaft concentric with the shaft for the rough tuning.

Still another object of the present invention is the provision of a fine tuning mechanism that permissibly slips when rotated beyond fixed limits.

The novel features that are considered characteristic of this invention are set forth in the appended claims. The invention, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in conjunction with the drawings, in which:

Figure 1 is a top view of the printed base of a tuner embodying my present invention.

Figure 2 is a top view of the assembled circuit com ponents of my novel tuner.

Figure 3 is a schematic drawing of the circuitry of the tuner of my invention.

Figure 4 is a side view of the fine tuning element of the present invention.

Figure 5 is a side view of the unit of Figure 4.

Figure 6 is a perspective view of the fine tuning element of the present invention.

Figure 7 is a sectional view of a portion of the stepping mechanism of my present invention.

Figure 8 is a series of reactance vs. shaft rotation curves.

Figure 9 is a top view of a printed tuning inductor of the present invention.

Figure 10 is a sectional view of the driving elements of my invention.

Figure 11 is a partially exploded view of the chassis and driving elements.

Figure 12 is an exploded view of the driving element.

Figure 13 is a front view of the chassis.

Figure 14 is a top view of a printed tuning inductor of the present invention.

Figure 15 is a top view of a printed tuning inductor of the present invention.

Figure 16 is a top view of a printed tuning inductor of the present invention.

Figure 17 is a bottom view of the printed base.

Figure 18 is an exploded view of the printed base and the components mounted thereon.

Figure 19 is an exploded view of the printed base and printed coils of the present invention.

Referring to Figure 11, a chassis 121 has a front panel 122 and supports a base 20, hereinafter described. The front panel 122 supports the notched member 123 by means of two screws 124 and 125 over the opening 126. The screws 124 and 125 fit through the holes 127 and 128 in the notched member 123 and thread the holes 129 and 130 in the front panel 122. The notched member 123 has a centrally located multi-toothed opening 131, which opening 131 seats a brass bushing 132, shown also in Figure 12.

The bushing 132 rotatably supports a shaft 133, which is the rough tuning or channel selector shaft. The shaft 133 has a milled portion 134 which supports a knob, not shown, and a hollow fine tuning shaft 160, hereinafter described.

The end 136 of the shaft 133 has two diametrically opposed milled faces 137 and a pin 138 as an integral part thereof. The end 136 protrudes from the bushing 132 and fits into the opening 139 of crank member 140. The crank member 140 has diametrically opposed arms 141 and 142 having the holes 143 and 144, respectively.

The openings 148 and 149 are located in the sections 150 and 151 which join the two units 152 and 153 of the resilient member 147. The unit 152 is elliptically shaped and has two diametrically opposed openings 154. The openings 154 seat ball bearings 155 against the notched member 123. The diameter of the opening 154 is slightly smaller than the diameter of the bearings 155. The bearings 155 are seated between the rounded notches 156, shown more particularly in Figure 7.

The rotation of shaft 133 causes the crank 140 hearing resilient member 147 to rotate. The rotation of the resilient member 147 causes the bearings 155 to ride over the notches 156 to a subsequent position between two other notches 156.

The other unit 153 of resilient member 147 is also elliptically shaped and is bent at 157 and 158 to resiliently supported a disk 159, hereinafter described, shown in Figure 11.

The spring member 147 provides a symmetrically balanced detent mechanism in which the required spring force or tension is evenly divided and so eliminates any side thrust or distortion of the main driving shaft.

The spring member 147 also provides the thrust force which force is required to hold the tunable element of coil boards 25, 40, 49 and 76 against the pivot point 170, hereinafter described. The member 147 has a third function by providing the tuning force or torque required to turn the movable tuning elements. This action is accomplished through the two fingers or protrusions X (Figure 12). The fingers X provide spring tension in the direction of the main drive shaft 169 being supported by the two bent supporting portions 157 and 158 of the spring member 147.

The advantages of this type of construction is that one unit or stamping for the part 147 essentially serves shaft 169 all rotate together.

as two or three more separate springs, levers or members necessary to accomplish the functions of positioning the tuning element in the chassis, of providing the turning moment for the tuning element, and of providing for adequately detenting or stopping the tuning element in accurately controlled position or positions.

The main tuning element or drum consisting of the printed coils is supported between pivots 179 and 138 and the driving moment is provided by the two points X of the spring 147.

Any slight misalignment of the sometimes long tuning shaft 161 will not throw any distortion or strain on the main tuning assembly. The distortion or strain is taken up by the spring action of member 167 which the fingers X then move in the corresponding slots 159a and 195a in member 192, hereinafter described.

The shaft 133 described above supports a hollow shaft 160. The hollow shaft 168 is milled at one end 161 to support a knob, not shown.

At the other end 162 of the hollow shaft 168 is rigidly attached a coil spring 163. The spring 163 may be fixed to the shaft 16 by brazing or by tight threading or by any other means known in the art. The spring 163 is in frictional relationship with a resilient member 164. The resilient member 164 is shaped as the sector of a circle and has two extensions 165 and 166. The member 164 is rigidly supported on a shaft 167 either by awelded connection or otherwise.

The rotation of the hollow shaft 161) causes the rotation of the resilient shaped member 164 and thus the shaft 167.

The contact between the spring 163 and the resilient member 164 is a high frictional one. The resilient member 164 is deformed against the spring 163. The contacting .arcuate edge 168 of the member 164 bears tangentially against two surfaces of the spring 163 as it fits into the space between the coils of the spring 163. The construction results in a substantially positive drive with no slippage.

The extensions 165 and 166 come into contact with the spring 163 and prevent further rotation of the resilient member 164. Further rotation of the hollow shaft 160 causes slippage between the resilient member 164 and the coil spring 163.

The shaft 167 performs the fine tuning in a manner hereinafter described.

The pin 138 helps support a partially hollow shaft 169. The shaft 169 is suspended between one support, the pin 138 on the front panel 128 and upon a hearing pin 170, as shown in Figure 11, on a back panel 171. The shaft 169 has firmly attached to the front thereof, as is hereinafter described, a cylindrical member 192. The member 192 is removably attached to the resilient member 147 at points X, described above,

so that upon rotation of the shaft 133, the crank 14%),

the resilient member 147, the member 192 and the The shaft 169 also carries four tuning inductors or printed coils 25, 40, 49 and 76, hereinafter described, and shown in Figures 14, 15, 16 and 9, respectively. The tuning inductors 25, 40, 49 and 76 bear against spring contacts 196, 197, 198 and 199, as shown in Figures 2, 11 and 18, and have conductive paths a, 46a, 49a and 76a, respectively.

The printed coils 25, 40, 49 and 76 are each essentially a number of individual coils in series or one complete series coil in which taps are taken off at the exact inductive position necessary for each of the 12 television channels or frequencies.

The success of these coils lies entirely in the geometric configuration which is so arranged that the normal position of each tap is taken off having the inductance at the proper value for the consecutive television station or frequency. Any change in the configuration of the coil or overall size of the coil will therefore throw the conductance out of range of the particular television frequency.

A further advantage of this type of construction in which the coil rotates and in which all coils in this configuration are in series is that this construction eliminates all necessity of further soldered connections or joints or the necessity of adding any external inductance. In other words, after the coil is etched, fabricated and punched out there are no further soldering operations or any further electrical connections to be made to the coil. The inductance is complete as etched and only requires for operation that contact be made to it by the spring clips 196--199, described above.

The rotation of shaft 133 as described above by means of a knob, not shown, causes the tuning inductors 25, 40, 49 and 76 to rotate, changing the tuned frequency to which the set is tuned.

The coil board 25, 4t), 49 and 76 is rigidly fixed in position by the plastic bushings 192-195, and 195a, which slide on the shaft 169; 195a being behind the disc 76 and thus not shown. The bushings 192195 and 195a each have a longitudinal groove 19512 through which a plastic rod 2% fits. The rod 2% passes through the holes 25b, 46b, 49b and 76b of the inductors 25, 48, 49 and 76, maintaining them' rigidly in position.

The shaft 167, as shown in Figure 11, and more particularly in Figures 4, 5 and 6, carries a variable condenser unit, hereinafter described. The shaft 167 is positioned on the back panel by means of a hole 172 and on the front panel 126 by means of a slot 173, having a groove 174 which fits into the slot 173. The shaft 167 has rigidly attached thereto a partially circular dielectric member 175. The partially circular dielectric member 175 has rigidly attached thereto by means of a rivet 176 a plate assembly 177. The plate assembly 177 is thus insulated from the shaft 167. This insulation is provided to eliminate sliding contacts wherever possible since sliding metallic contacts contribute appreciably to the noise during the operation of a fine tuner.

Another reason for insulating the plate assembly 177 is to reduce the amount of coupling of oscillator energy to the shaft 167.

The plate assembly 177 comprises two metallic plates 178 and 179 which are connected by means of a connection 181), all of which are integral parts of the plate assembly 177.

The rotation of shaft 167 by means described above in reference to Figures ll, 12 and 13 causes the, dielectric member 175 and the plate assembly 177 to rotate. The rotation of the plate assembly 177 causes the plate assembly 177 to rotate over a U-shaped conductor 181 which is rigidly attached to the base 132 by means of two rivets 183 and 184. The plate assembly 177 also rotates over a substantially rectangular member 185 which is seated centrally in the opening of the U-shaped member 181.

The rectangular plate 135 lies substantially in the same plane as the space 186 which is between the two plates 178 and 179 and also in the same plane as the U-shaped member 181. The U-shaped member 181 and the rectangular plate 185 are essentially of the same thickness and preferably of the same conducting material having approximately a of an inch rectangular gap between the rectangular member 185 and the U-shaped member 181. The central rectangular plate 185 is connected to the base 182 of the tuner. The rotation, then, of the plate assembly 177 increases the capacity between the U-shaped member 181 and the rectangular member 185. The increasing capacity is due to two series capacitors, one from the U-shaped member 181 to the plates 178 and 179 and the other from the movable plates 178 and 179 to the rectangular plate 185.

The reason for the above construction is to provide an approximately equal fine tuning range on high frequency channels as well as the low frequency channels. Since the high frequency band is approximately two to three times the frequency of the low frequency band, the percentage change of frequency when capacitance change alone is used for fine tuning is substantially constant. Thus an equal rotation of the fine tuning knob will now cause a greater variation in frequency at the upper band channel frequencies than at the lower band channel frequencies.

When operating on the high frequency band, the fine tuning tends to become rougher, giving greater variations and making it harder to tune accurately. The construction as shown in Figures 4, 5 and 6 alleviates this condition by introducing a variation in inductive reactance in the U-shaped member 181 due to eddy currents. The variation in inductive reactance on the low channels as illustrated in Figure 8 on the curve marked D is practically negligible as the shaft is rotated. The variation in inductive effect, however, on the high channels as illustrated by the curve marked C is substantial and the frequency change produced by this variation is correspondingly large. This frequency change produced by variation in inductive reactance is in opposition to the frequency change produced by the simultaneous change in capacitance.

The tuning range on the low channels is shown by the dashed curve A. Curve A is the approximate curve which is the desirable tuning range on the high channels. The tuning range of the capacitor alone on the high channels is illustrated by the curve B. Combining the effects of curve B, the tuning range of the capacitor alone on the high channels, together with the inductive effect on the high channels, curve C produces a resultant tuning range on the high channels as illustrated by curve E. Thus if the high frequency was, say three times as great as the low frequency, an equivalent inductive reactance, which would be approximately two-thirds the capacitive reactance, would be introduced at this high frequency, leaving an equivalent capacity of one-third the capacitor resulting in a tuning range which is substantially the same as on the low frequency. The result of this construction is a fine tuning means which gives substantially the same tuning frequency range on the high band channels as on the low band channels.

The base 20 described above is a printed base and is hereinafter described in reference to Figures 1, 2, 3, l7 and 18.

Referring now to Figures 1, 2, 3, 17 and 18, the terminals 21 and 22 are the input terminals to the printed base 20. Figure 17, which is the bottom view of the printed base 20, and Figure 18, show the physical point of connection to the terminals 21 and 22 whereas Figures 3, 1 and 2 show the electrical equivalent in the circuit and as a printed portion on the top of the printed base 20. The input terminal 21 is connected through an impedance transformation capacitor 23 (Figures 3, 17 and 18) to the terminal 24. One of the electrodes of the capacitor 23 is connected to the terminal 21 and the other to the terminal 24. The capacitor 23 essentially transforms the input impedance of 300 ohms to an approximate impedance of 1000 ohms. This higher input impedance allows the antenna tuning inductor 25 (Figures 3, 11, 14 and 19), described above, to operate with proper loading.

The terminal 24 is connected through a loading resistor 26 (Figures 3, l7 and 18) to the terminal 27 which is electrically the same as terminal 22.

The loading resistor 26 has comparatively large resistance and so effectively maintains the impedance of the circuitry associated with the inductor 25 fairly constant over the complete television band width. The terminal 24 is also connected to terminal 28 through an inductor 29 which is a lumped printed inductance on the printed base 20, shown specifically in Figure l.

The inductor 29 allows tuning to the frequency of channel 13 with a minimum of inductance on the coil board inductor or antenna tuning inductor 25. The inductor 29 may be a variable inductor to compensate for variations in the manufacture of the inductor coil board 25. The inductor 25 is connected between the terminals 28 and 30, described above; the terminal 30 being at ground potential as indicated at Figure 3.

The terminals 30, 27 and 22, as shown specifically in Figure 1, are all points on the large metallic surface 19, hereinafter described, which is at ground potential. The

inductor 25 is positioned as is also hereinafter described in a plane that is perpendicular to the base 20 and makes contact with two leaf springs 196 which are riveted to the base 20 at terminals 28 and 30 described above and shown in Figures 2, 11 and 19.

The surface 19 containing the terminals 22, 27 and 30 is connected to the cathode 31 of the triode tube 32. The triode tube 32 is shown only in Figure 3 and may be a 6AB4 tube, acting as a radio frequency amplifier. The triode 32 has its prongs (not shown) which fit into the openings 18 in the tube base 17. The tube base 17 is riveted at 17a, 17b and 17c (Figures 2, 17 and 18) to the base 20 and is so rigidly fixed thereto. The openings 18 enclose two resilient arms 16 (Figure 2) which seat the prongs of the tube 32 and thus seat the tube 32 rigidly in the base 17. The base 17 also contains a plurality of lugs 15 (Figure 2) which make contact with prongs of tube 32 and with the surrounding circuitry. The lug 15 connected to the prong leading to the cathode 31 is connected to the surface 19 at point 14.

The terminal 24 described above is connected through an impedance transformation capacitor 34 (Figures 3, 17 and 18) to the grid 33 of the triode 32. The capacitor 34 connects through the base 20 to the printed portion 13 (Figures 1, 2 and 18) which is soldered to the lug 15 connected to the prong leading to the grid 33. The impedance transformation capacitor 34 allows the tuning of the antenna inductor 25 with reduced grid capacity loading.

The grid 33 is connected to an automatic gain control unit 35 (not shown) through an isolation resistor 36 (Figures 3, 17 and 18). The circuitry of automatic gain control units is well known in the art and is therefore only indicated by an arrow in Figure 3. The resistor 36 is connected through the board 20 at point 35a to the external terminal 35b which subsequently connects to the automatic gain control unit 35.

The triode tube 32 is neutralized by means of a split capacitor arrangement in the plate circuit, as is hereinafter described. The plate 37 is connected at 37a (Figures 1, 2 and 18) to the board 20 and through a trimmer capacitor 38 (Figures 2, 3 and 18) to ground at surface 19. The capacitor 38 compensates for the diflFerences in capacity of different tubes 32 that may be used and allows tuning of the variable inductor or coil board 40, hereinafter described in reference to Figures 15 and 19, being the tuned plate inductance. The trimmer capacitor is adjusted by a screw 39 shown in Figures 17 and 18.

The plate 37 is connected to the variable inductor 40 through an inductor 41 which is essentially a lumped inductance. Inductor 41 can also be made variable to help compensate for variations in the manufacture of the coil board 40 or for variations in the tube capacities.

The inductor 41 has mounted thereon a leaf spring 197 which makes contact, as is hereinafter described, with the coil board 40. The plate 37, described above, is loaded by means of a load resistor 42 (Figures 3, 17 and 18) connected across coils 40 and 41 and a resistor 57 (Figures 2, 3 and 18) which is connected across the leaf springs 197. The load resistor 42 loads the total plate tuning and has the greater effect on the high channels.

The low channels are tuned by the coil 40 which is composed essentially of low channel coils. This loadmg procedure tends to give a fairly uniform tuning range on all the channels.

The inductor 40 is connected through the second spring leaf 197 to the neutralizing capacitors 44 and 46. Capacitor 46 returns to the grid 33 of the triode 32, and the capacitor 44 returns to ground 43 as shown in Figures 2, 3, 17 and 18.

The trimmer capacitor 46 is mounted above the base 17 and is supported by means of the wire leads 46b and 46a, which are attached to the grounded spring leaf 197 and the cathode lug 15, respectively. At this point in the plate circuitry the neutralization is constant or practically constant on all channels. The resistor 47 (Figures 3, 17 and 18) connected to point 45 (Figures 1, 2 and 3) is the plate driving resistor and also acts to isolate the circuit from the B-lat the external terminal 48. The external terminals are terminals on the printed circuit board 20 protruding from the chassis and are connected thereto from the outside.

The circuitry associated with the tube 32 as described above is designed to be very compact and of high economy as a great portion of the circuitry printed is on the base 20. The tube 32 is a radio frequency amplifier tube which feeds into a converter section simultaneously with the output of an oscillator, as is hereinafter described, to get a fixed intermediate frequency output from the converter.

The output from the tube 32 is coupled through the inductor 40 as is hereinafter described in reference to Figure 19 to an inductor 49 (Figures 3, 11, 16 and 19). The inductor 49 is a printed coil board somewhat similar in construction as the inductors 40 and 25 and is connected through a printed inductor 53 (Figures 1, 2, 3, 18 and 19) to the grid 52 of a triode 50.

The inductor 53 is essentially a lumped inductance which may be variable and has essentially the same effect as the lump inductance 41 in the plate circuit of the triode 32. The triode 50 in the present modification is part of the double triode 51 (Figure 3).

The double triode 51 is mounted on a base 51a which is similar in construction to the base 17 described above.

The tube base 51a is rigidly attached to the base 20 by rivets 51b, 51c and 51d (Figure 2) and has opening 51e (Figures 2 and 17) to seat the prongs, not shown, of the double triode 51. The prongs are connected through the connecting lugs 11 (Figure 2) to the surrounding circuitry.

The inductor 53, described above, is connected to a lug 11 of the triode 50 at 53a (Figures 1, 2, 18 and 19) on the printed board 20. The lug 11 at point 53a connects to the grid 52 (Figure 3) of the triode 50.

The triode 50 acts as a converter tube as in hereinafter described.

The grid 52 is connected to ground through the converter grid trimmer capacitor 54 (Figures 2, 3 and 18) which has a range from /2 a micromicrofared to 3 micromicrofarads. Capacitor 54 is adjusted by means of the adjusting screw 54a (Figures 17 and 18). The grid 52 is also connected to a 220,000 ohm grid resistor 55 (Figures 3, 17 and 18) and thence to ground at 58 (Figures 2, 3, l8 and 19) on the surface 10, and to the grid coupling capacitor 56 (Figures 3, 17 and 18). The grid coupling capacitor 56 has only 20 micromicrofarads capacitance in order to permit tuning with the printed coils, hereinafter described. The grid 52 of the triode 50 returns then to point 58 on the printed surface through inductors 53, 49 and capacitor 56.

The cathodes 59 and 60 of the double triode 51 are grounded to point 59a and 60a which is also on the sheet of copper 10 on the printed board 20. The plate 61 of the converter 50 of the double triode 51 is connected to the parallel combination of a resistor 62 and inductor 63, (Figures 2, 3 and 18). The inductor 63 is physically a long lead which is wound on the resistor 62 so as to conserve space. The resistor 62 and inductor 63 combination has been found to give optimum results with regard to the grid loading at grid 52 on the high channels. The Q of the inductor 63 is thus lowered by the resistor 62 and results in a flattened frequency response. The inductor 63 and resistor 62 are connected to the output intermediate frequency coil 64 (Figures 2, 3 and 18) which is grounded at both ends through the capacitors 65 and 66 respectively (Figures 2, 3 and 18). The capacitor 65 in conjunction with the capacitor 66 tunes the coil 64 to approximately megacycles. To increase the tuning range inductor 64 is provided with an iron core indicated at 100a in Figure 3.

The coil 64 is coupled to a coupling loop 67 (Figures 3 and 18) which enables the output of the tuner to be coupled to the rest of the television set. The coupling loop 67 is connected to two external terminals 68 and 69 as seen in Figures 2, 17, 18 and 19, which protrude from the outside of the printed board 20 and are connected through the lines 92 and 93 (Figure 17). The coupling loop 67 couples to the first intermediate frequency tube, not shown. Enough coupling has been provided from inductor 64 by coil 67 to provide adequate coupling to the first intermediate frequency stage of the television set. The coil 67 has five turns wound on the coil 64, which is constructed of twenty-five turns of #40 wire. Link type coupling is provided to reduce oscillator radiation.

The converter tube 50 is neutralized to reduce the amount of reflection of the intermediate frequency in the radio frequency pattern by providing a neutralizing capacitor 71. The neutralizing capacitor 71 has 2 /2 micromicrofarads capacity and is coupled to the grid 52 of the converter tube 50. The output coil 64 is connected to the converter plate load resistor 72 (Figures 3, 17 and 18) which is a 4700 ohm resistor. The resistor 72 is connected to the resistor 47 described above by the printed lead 72a (Figures 1, 2, l8 and 19) and does not load the neutralizing arrangement as described above, since the neutralizing voltage is taken from point 73 (Figures 1, 2 and 18)where the 20 rnicromicrofarad tubular capacitor 66 connects to ground. This construction is another split capacitory type of neutralization as described above and is not critical due to the single frequency operation at 20 megacycles, which is the frequency of the output.

The oscillator section is associated with the triode 74 of the double triode 51 and contains a parallel combination of inductors 75 (Figures 2, 3 and 18) and 76 (Figures 3, 9 and 11) which isv connected to the grid 81 of the triode section 74 through a capacitor 82 (Figures 3, 17 and 18). This parallel combination of the inductance 75 and 76 is essentially the tuning inductance which determines the frequency at which the oscillator operates. The inductance 76 is the tunable inductance or the coil board inductor which is connected to a shaft and turned with the other coil board inductors, as described above. By varying the inductance 75 by means of the screw 75a (Figures 17 and 18) it is possible to vary the oscillator frequency without moving the variable inductor 76. This provision is necessary as the printed coil 76 is fixed on the shaft with the other printed coil boards 25, 40 and 49, described above.

Two other adjustments have been provided which can be made at the factory. The two adjustments consist of the variable inductor 11 (Figures 2, 3 and 18) and the variable capacitor 79 (Figures 2, 3 and 18). The variable capacitor 77 is a small lump inductance which is connected in series to the parallel combination of the inductances 75 and 76 and is adjusted by means of the screw 77a (Figures 17 and 18). The other end of the inductor 77 is connected to the trimmer capacitor 78 which is adjusted by means of the screw 79a (Figures 17 and 18) and thence to ground on base 10. The trimmer capacitor 78 compensates for variations in the rated capacity and the inductor 77 compensates for inductance variation on the high channels. These three means of adjusting the oscillator frequency are provided to give proper tracking of the oscillator on all channels. The inductance 77 effects only the high channel tuning and has no effect on the low channels due to its relatively small value.

The fine tuning is accomplished by fine tuning element 80 (Figures 2 antd 18) which is hereinafter described in detail with reference to Figures 5, 6 and 7, connected from the plate 88 of the tube 74 to the trimmer capacitor 78. 1The lug 11 from the plate 88 is shown in Figure 2 as 1 a.

The grid 81 is connected through a conventional grid leak resistor 84 (Figures 2, 3 and 18) to ground at 85 (Figures 1, 2, 18 and 19) and through capacitor 82, described above, and capacitor 86 (Figures 3, 17 and 18) to ground 87 (Figures 1 and 2). The injection to the converter 50 from the oscillator 74 is accomplished by means of the capacitor 89 (Figures 2, 3 and 18) which connects the grids 52 and 81. The capacitor 89 has two microfarads capacity and in conjunction with the circuitry arrangement of the oscillator provides a constant injection voltage to the converter section 50.

B+ from terminal 48, described above, is supplied to tlienoscillator through the resistor 91 (Figure 3, l7 and The filaments 97 and 98 (Figure 3) of the tubes 32 and 51, respectively, receive a 6.3 volt supply through terminal 99 (Figures 1, 2, 3, 18 and 19). Terminal 99 is connected through printer inductor 100 (Figures 1, 2, 18 and 19) to filament 97 and through an inductor 101 to filament 98 and simultaneously through tubular capacitors 102 and 103, respectively, to ground.

The tubular condensers 102 and 103 are fitted into slots 102A and 103A (Figures 1 and 18) in the base 20, to form a compact and strong structure.

As described above and as shown specifically in Figures 11 and 19, the low channel coupling between the radio frequency tube 32 and the converter triode 50 is accomplished by means of the relative positions of the induce tors 40 and 49. The field of the inductor 40 crosses the inductor 49 and thus accomplishes inductive coupling on the low channels. The coupling remains approximately constant on each of the low channels at a value in the neighborhood of 4 /2 megacycles. The mutual inductance of the inductors 40 and 49 is not effective on the high channels due to the coil construction.

The coupling on the high channels is accomplished by the relative positioning and direction of current flow in the printed circuit of the lump inductances 41 and 53 so as to be essentially inductive coupled. The inductors 41 and 53 are positioned parallel to each other on printed board circuit 20, and as shown more specifically in Figure 19, are formed in position so as to be predominantly inductive coupled, i. e., with a minimum of capacitive coupling. The coupling on the high channels is nearly constant having a flat response over approximately 4 /2 megacycles for each channel.

One of the important features of the printed circuit tuner described above is that the oscillator converter tube 51 and associated circuitry of the tuner has a ground plate 10 on the printed board 20 to which all of the circuit grounds are made. This in turn is grounded to the metal chassis 121 hereinafter described at one point only. Similarly, the ground plate 19 printed on the printed board 20 has connected to it all of the circuit grounds for the radio frequency or amplifier section of the tuner which in turn is grounded to the metal chassis 121, described above, at another point near the antenna input. These features reduce oscillator radiation since there is less chance for a circulating current in ground plate 19 or chassis 121 to cause energy from the oscillator to be inducted into the radio frequency section of the tuner. There is no physical connection on the printed plate 20 itself between the two ground plates 10 and 19, the one in the oscillator converter and the other in the amplifier.

If such a current would flow in the chassis between various grounds of the radio frequency section and the oscillator section it would very likely lead to excessive oscillator energy being transmitted through the radio frequency section and into the antenna.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

I claim:

1. In a tuning device having a plurality of individually selectable pre-tuned elements; a rotatable shaft for effecting the selection of said pre-tuned elements; an additional infinitely variable tunable element rotatively operable between predetermined limits on a shaft having an independent axis displaced from said first mentioned rotatable shaft; co-axial operating member for said rotatable shaft and said variable tunable element comprising an operating shaft for said variable tunable element; means for rotating said first mentioned rotatable shaft; a sleeve rotatably mounted on said first mentioned rotatable shaft; means for rotating said sleeve; and a connection between said sleeve and said second-mentioned shaft, said variable tunable element being a variable capacitor unit; said unit comprising two parallel movable plates of conductive material, a U-shaped conductive member and a rectangular plate of conductive material, said rectangular plate lying in the same plane as the U-shaped member, said plane being a plane between said two parallel movable plates, said U-shaped member being essentially a variable inductor presenting negligible impedance on said lower frequency band and presenting an impedance approximately twothirds the impedance of said capacitor on said upper frequency band.

2. A tuning device comprising variable capacitive and inductive means, said capacitive means consisting of a plurality of plates, one of said plates being U-shaped to form said inductive means, another of said plates extending into the open side thereof, said two plates being positioned in one plane, and additional plates electrically interconnected on each side of the said plane for simultaneously decreasing the capacitance between the plates of the said plurality of plates and increasing the inductance of the said U-shaped plate at motion in one direction of said last mentioned plates with respect to the other mentioned plates.

3. A tuning device comprising variable capacitive and inductive means, said capacitive means consisting of a plurality of plates, one of said plates being U-shaped to form said inductive means, another of said plates extending into the open side thereof, said two plates being positioned in one plane, and additional plates electrically interconnected on each side of the said plane for simultaneously decreasing the capacitance between the plates of the said plurality of plates and increasing the inductance of the said U-shaped plate at motion in one direction of said last mentioned plates with respect to the other mentioned plates, operating means mechanically connected to and electrically isolated from the said additional plates.

4. In a television tuner having an upper and lower frequency band, fine tuning device having equal frequency variation on said upper and said lower frequency band, said fine tuning device comprising variable capacitive and inductive means, said capacitive means consisting of a plurality of plates, one of said plates being U-shaped to form said inductive means, another of said plates extending into the open side thereof, said two plates being positioned in the plane, and additional plates electrically interconnected on each side of the said plane for simultaneously decreasing the capacitance between the plates of the said plurality of plates and in creasing the inductance of the said U-shaped plate at motion in one direction of said last mentioned plates with respect to the other mentioned plates.

5. In a television tuner having an upper and lower frequency band, fine tuning device having equal frequency variation on said upper and said lower frequency band, said fine tuning device comprising variable capacitive and inductive means, said capacitive means consisting of a plurality of plates, one of said plates being U-shaped to form said inductive means, another of said plates extending into the open side thereof, said two plates being positioned in one plane, and additional plates electrically interconnected on each side of the said plane for simultaneously decreasing the capacitance between the plates of the said plurality of plates and increasing the inductance of the said U-shaped plate at motion in one direction of said last mentioned plates with respect to the other mentioned plates, the inductance of said U-shaped plate being of a magnitude such that it is essentially ineffective as an inductance in said lower frequency band and presenting a change in impedance of approximately two-thirds the change in impedance of the said capacitance means on said upper frequency band at movement of the said additional plates with respect to the other mentioned plates.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,341,345 Billiard Feb. 8, 1944 2,385,131 Garthwaite Sept. 18, 1945 2,521,963 Beusrnan Sept. 12, 1950 2,542,416 Kach et al Feb. 20, 1951 2,551,228 Achenbach May 1, 1951 2,558,482 Galitz June 26, 1951

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