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July 19, ' 1938- w. VAN B. ROBERTS 2,124,211 COMBINED AMPLIFICATION AND TUNING CONTROLS ' Filed Oct. 17, 1934 7Q J/é/V/IZ M 6 _ , 5 ¥ /0 5 ii + E INVENTOR - 114417519 #4” I._ #085973” BY / ‘ ATTORNEY 2,124,211 Patented July 19, 1938 UNITED STATES PATENT creme . 1 2,124,211 ' , COMBINED AMPLIFICATION AND‘ TUNING ‘ ' ' CONTROLS ‘ ' '- , ‘ Walter van B. Roberts, Princeton, N. J., as's‘ignor to Radio Corporation of America, a'corporation , v of Delaware Application October 17, 1934, SerialNo. 748,610 - ' . 1 claim; (01. 1795-171) My present invention relates to uni-controlled tuning and ampli?cation control adjustments for radio receivers, ‘and more particularly to novel and improved devices for'correlatingpthe ‘tuning 5 ‘ and radio frequency energy transfer character istics of the selector networks of radio receivers. One of the main objects of my present inven tion is to provide capacity coupled radio frequen cy ampli?ers wherein the'capacity coupling exists connection with the drawing in which IIhave in-, dicated diagrammatically several‘ circuit organi zations whereby my invention may be caried‘intoi effect. In the drawing:-— ‘' Fig. 1 shows a circuit diagram ofra. radio freev quency ampli?er embodying the ‘invention, and’ Fig. 2 shows the circuit ‘diagram of the ampli-i , ?er embodying one mechanical form of a come, 1 10 between‘a following tunable radio, frequency se bined tuning and ampli?cation control'device. :. ': transfer characteristic and the tuning character ferent ?gures designate similar circuit elements,‘ lector network and a'vpreceding non-tunable plate ‘circuit of a radio, frequency ampli?er; the energy istic of the coupled circuits being varied in such a 15 manner, and by such devices, that a predeter mined transfer characteristic over the entire tun ing range‘is secured with the capacity coupling as small as possible at' the high frequency end of the tuning range, ‘and as" large as convenient 20 at the low frequency end. , Another important object of the invention is Referring now to the accompanying draw ing, wherein like reference characters in the dif—' the radio frequency ampli?er of Fig. 1 shows a pair of- screen grid tubes I and 6 capacitatively 161 coupled by a condenser‘ C. The input electrodes, of ampli?er tube 1 may be considered arranged. for coupling to any source of signal energy. For example, the ampli?er network of Fig. l'may be considered as the radio frequency ampli?er of? a 20, superheterodyne receiver. In such case the .out to provide an adjustable capacity device between put electrodes of tube 6 may be adapted for ‘con the plate circuit of a radio frequency‘ampli?er and.’ a following tuning circuit, the adjustable nection to the‘ ?rst detector of the set, or the tube 6 may itself be the ?rst detector“ Of course,‘ the signal collector. may, in that case, be‘ connected to the input electrodes of ampli?er l, and a tun able selector circuit may be connected to the 25 capacity device mechanically cooperating with the variable tuning condenser of the tuning cir cuit to provide an adjustable capacitycoupling between the preceding plate-circuit. and the fol lowing tuning circuit, and the variation of the 30 capacity coupling being so related to the varia tion of the following tuning condenserthat a desired, energy transfer characteristic is - secured. Another object of the invention is tov provide input of ampli?er I. a l > ' ' ' ‘ If the ampli?er network is in areceiyer of the tuned radio frequency type, then the ampli?er I may be the ?rst tunable radio frequency ampli ?er, and the tube 6 may be the'second- tunable 30," radio frequency ampli?er, or it may be the de- y In any case the present invention is‘to be understood as havinga wide applicability; a novel type of tuning condenser for they tunable 35,v selector circuit of a radio frequency ampli?er, the tunable circuit being arranged for coupling to the untuned plate circuit of a preceding ampli tector. an auxiliary ‘condenser effectively connected 40 across the untuned plate circuit, and an auxiliary pair of rotor plates being provided on the rotor quency energy transfer characteristics of the coupling network so as to obtain a desired energy‘ transfer characteristic over the tuning range of whatever the nature of the circuits which are coupled, the problem to be solved by the present ?er, the tuning condenser being providedwith. invention is tovary theqtuning and radio fre-' shaft. ' ' ~ ~ - ‘ the receiver. _ provide especially simple and‘economical devices The plate of ampli?er l is connected to the low potential side of the usual grid biasing network 2' through a path which includes the radio fre 4,5, quency choke 3 and the source of plate voltage 4. for securing a predetermined energy transfer The frequency selection network ‘ comprises the characteristic over the tuning range of a radio coil 5,and the variable tuning condenser t connect: Still other objects of the invention are to im prove generally the efficiency of radio frequency 45 ampli?er networks of the tunable type, and to , ed, in shunt with the coil 5; the tunable circuit be‘ The novel features which I believe to be char; ing connected in series between the input grid ofv , 50 tube 6 and the low potential'side of the grid bias acteristic of my invention are set forth in par ticularity in the appended claim, the invention ing network ‘I. The coupling condenserlC con frequency ampli?er. itself, however, as tov both its organization and method of operation will best be understood by 55 “ reference to the following description taken in nects the plate side of choke 3 to the high alter nating voltage side of the following tunable cir~~ cuit. The problem presented for solution bylthe 2 2,124,211 invention of the present application is to vary the tuning of the tunable input circuit of tube 6 over the tuning range of the receiver, and yet necessary to show the side view of the condenser plates, or the housing construction of the plates maintain a desired and predetermined radio fre of the manner of constructing such condensers quency energy transfer through the coupling con denser C over the entire tuning range of variable condenser t. of the variable type. The pro?le of the plates of condenser S are cut to give any desired variation of condenser S with respect to the variation of tuning condenser t. because those skilled in the art are fully aware Fig. 1 shows the manner of securing such a re lationship, or rather such a correlation of tuning The two» condenser assemblies S and t are located 10 and energy transfer, and it is also accomplished , far enough apart on the shaft so that the stray 10 in a simple, effective and economical manner.‘ capacity between stators is smaller than the An auxiliary condenser S is connected across the smallest‘value of coupling capacity desired at C. plate circuit of tube I, and in shunt with con The disposition of a grounded shield 8 between the densers C and t. The magnitudes of condensers adjacent stators l3 and I2 will reduce the re 15 S and C are so chosen, and their rates of varia- .1 quired separation, but the separation should not 15 tion are uni-controlled with the variation of con be reduced too much, or the minimum capacity denser t in such a manner, that a predetermined of condensers S and t will be increased too much energy transfer characteristic can be secured. by the close proximity of their stators to the Such a characteristic may be of the uniform, or grounded shield 8. 20 ?at, gain type; that is to say, the ampli?cation The variable capacity C consists of the metal 20 of the signal energy will be substantially uni form over the tuning range of the receiver em bodying the ampli?er network shown in Fig. 1. To preserve as large a tuning range as possible, 25 say over the broadcast band which is between 500 and 1500 kilocycles, the value of condenser C should be as small as possible at the high fre quency end of the tuning range of the receiver; it should be as large as ‘convenient at the low fre 305 quency end. It is not believed necessary for the purposes of the present application to present the theoretical considerations which support the pre mise that for a given set of other conditions‘, the value of condenser C required for a given am pli?cation depends upon the value of condenser S; It will be sufficient to point out that such a premise is established in an analysis entitled “Maximum Ampli?cation In Capacity-Coupled Circuits”, ‘appearing on page 20 of Electronics for 40 July, 1931. It can now be stated that it is the purpose of sulation material l0, such as a collar of insula tion material, is carried by the shaft 9, and the bolt‘ I5 is disposed within the collar. ' of plates 16, l?'iwith rotors l4 and H. Plate I6 30' is disposed adjacent the end stator'l2 of condenser 15, while plate i6’ is disposed adjacent the end stator I3 of condenser S. The plates l6’ and Hi cooperate with their adjacent stator plates to provide the condenser C. Hence it will be seen 35" that as'shaft 9 is‘ varied the capacity values of condensers S, C and t are varied. The conductor comprising plates l6 and I6’ is not electrically connected to any portion of the circuit,'but serves to vary the effective separation between the sta- ,' tors of condensers S and t. The blade pro?les of the present invention to vary the capacity value the conductor element Iii-I6’ are also cut to give any desired variation of capacity C with re spect to the'capacities t and S. In other words, the capacity between the adjacent end stators of condensers S and t constitutes the capacity which couples the high alternating potential side of con 45 be required to assume a small value at the high‘ frequency end of the tuning range and arrelative ly large value at the lower frequency end. In Fig. 1 the dotted lines U designate the mechanical uni-control arrangement for varying the three 50 condensers. This mechanical variation of the condensers should, of course, be accomplished in an economical, effective and simple manner, and without the use of sliding contacts or “pigtail” connections. In Fig. 2 such a mechanical construction is shown. The normal condenser construction is utilized for the condensers S and 15. That is to say, rotors l4 and II are mounted on the uni control shaft 9; stators l2 mesh with rotors H, 60 and stators 13 mesh with rotors M. The capacity provided between plates I3 and I4 is connected to provide the condenser S, while the capacity be tween plates l2 and II furnishes the tuning con denser t. It is to be understood that the well known type 65 of “bathtub” gang condenser may be utilized for ‘this purpose, and the shaft 9 will be understood as additionally being connected to, and support ing on it, the rotors of the tuning condensers of 70 other ampli?er stages. The auxiliary plates l4" and I3 may be used in conjunction with each tuning condenser of each stage. For the pur pose ofsimplicity, however, the construction be tween a given pair of ampli?er tubes is only con sidered. It will also be understood that it is un 25 The collar I0 is rigidly connected to shaft 9 so that adjustment of shaft 9 results in movement of condenser S in such a fashion that for a desired ampli?cation characteristic the condenser C will 55 conductor composed of two plates l6, l6’ metallic ally connected together by a bolt l5. This con ductor is insulated from shaft 9, although me chanically adjustable therewith. A block of in denser S to the high alternating potential side‘ of the tunable circuit of ampli?er 6. The value of this inter-stator capacity is varied by the plates 50 It and I6’, and the disposition of these plates be tween the adjacent end stators is varied at a rate dependent upon the rate of variation of the ca pacities of condensers S and t. It is not be lieved necessary to go into any further detail con 55 cerning speci?c pro?les for the blades of the condensers, since such pro?les can be easily de termined by those skilled in the art when it has been decided what. the ampli?cation character istic is to be; As stated before a speci?c type of 60 such characteristic is one that is uniform over the receiver tuning range, and in Fig. 2 it is to be understood that the capacity’ values of con densers S and C are varied with the variation of condenser t so that the transfer of radio fre 65 quency energy to the output circuit of tube 6 is substantially uniform over the tuning range of the receiver. It will now be appreciated that this relation of ampli?cation and tuning has been secured in a highly economical and simple fash ion,‘and without sliding contacts. For a further disclosure of the manner of con structing a variable condenser of the type shown in Fig. 2, reference is made to application Serial No. 387,148 of J. L. Bonanno, ?led August 20, 1929, 3 2,124,211 issued as Patent No. 2,040,426 o'nMay 12, 1936, wherein there is claimed, as well as disclosed, the organizations shown and described, but that many modi?cations may be made without departing type of variable condenser shown in Fig. 2, and ' from the scope of my invention, as set forth in the ' the manner of varying the inter-stator capacity appended claim. provided between adjacent variable condensers using a. common rotor shaft. In the above Bon anno patent the variation of the inter-stator capacity is used to vary the coupling between a pair of coupled tunable circuits of a band pass .10 network; in the present application the variable condenser construction of the Bonanno patent is What I claim is: V , In combination in a high frequency network which comprises a ?rst tube having an untuned plate circuit‘ which includes a radio frequency choke and a shunt capacity, a second tube pro vided with a tunable circuit, a condenser coupling‘ 10 the plate circuit of the ?rst tube to the tunable used to secure ‘a predetermined ampli?cation , circuit, and means including a common control characteristic over the tuning range of the re ceiver. 15 , . . » r 7 While I have indicated and described several for simultaneously varying the value of said shunt capacity, coupling condenser and the tun- ' ing condenser of the tunable circuit whereby a 15 systems for carrying myinvention into e?ect, it uniform energy transfer is‘ obtained over the will be apparent to one skilled in the art that my tuning range of the network. invention is by nomeans limited to the particular ' / WALTER VAN B. ROBERTS.