Патент USA US2119315код для вставки
'May 31, 1938. ' w, BUSCHBECK _ 2,119,315 NEUTRALIZING CIRCUIT FOR SCREEN GRID TUBES Filed April 3, 1935 ' 2 Sheets-Sheet 1 (‘.4 77-1005 (OI/7190! ourpw~_+ INPUT ' INVENTOR ‘ WERNER BUSCHBECK BY “ > ATTORNEY ' ' May 31, 1938. w. BUSCHBECK 2,119,315 NEUTRALIZING CIRCUIT FOR SCREEN GRID TUBES‘ 129. 5A Filed Alz‘fil 3, 1955 2 Sheets-Sheet 2 ‘ INVENTOR WERNER BUSCHBECK ‘BY WM’ ATTORNEY Patented May 31, 1938 2,119,315 UNITED . STATES PATENT ‘OFFICE 2,119,315 ' NEUTRALIZIN CIRCUIT FOR SCREEN-GRID TUBES Werner Buschbeck, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Tele-' graphie m. b. H., Berlin, Germany, a corpora tion of Germany Application April 3, 1935, Serial No. 14,494 In Germany April 3, 1934 4 Claims. The present invention is concerned with ways and means adapted to neutralize or compensate residual capacitances existing , in screen-grid tubes between the control electrode and the 5 plate, and which are especially suited for short Wave. systems. ‘ Owing to the presence of the’ screen-grid‘ the capacitance existing between plate and control electrode is effectively diminished. The residual 10 capacitance which may remain is neutralizable with such means as are known from triode tubes as long as this assumption is ful?lled; that the screen-grid so far “as alternating “current‘volt age is concerned is at cathode potential. And this assumption may be suppo‘sed'tb belpracti cally satis?ed where not unduly high tube ca pacities are dealt with, where the waves are ‘long, and where an adequately high blocking condens er is provided between the screen grid and the cathode. Where‘ however shorter waves are concerned, and ‘where screen-grid tubes are de screen-grid and the cathode (Ls) to secure per fect neutralization for a very de?nite wave length. However, such neutralization is inade quate in practical working inasmuch as it would be lost and lacking as soon as there is a change in the wave-length, while the restoring of the state of neutralization would be attended with a 10 good deal of tedious and time-consuming read justment in every given instance. The ‘present invention, therefore, discloses ways and means incorporated in a circuit organization whereby neutralization of the residual capacitance be 15 tween control grid and plate will be insured un der conditions unaffected by the wave-length or frequency. According to the invention, by the simulation of all of the capacitances existing inside the tube, 1' is no longer satis?ed. ' Of necessity, the connect ing leads between the‘ electrodes and the lead missible‘to disregard the capacities existing be in points or seals across the vacuum vessel (with tween plate and cathode, or between screen-grid ‘ the exception of the plates in water-cooled tubes) and cathode,>which anyway are always inherent are of a certain length and thus have an induc ly small. tive reactance which," where short-waves are involved, is no‘ longer negligibly small in com basic idea of the invention are shown in the ac . 25 ‘ A number of exempli?ed embodiments of the parison with the capacitive reactance residing in‘ the correspondingintermediate-electrode ca--v companying drawings, wherein Fig. 1A is a 30 screen-grid circuit neutralizing arrangement ac pacitances. Even if the supposition were ‘made that the‘ capacity interposed between the screen cording to the invention; Fig. 1B is a circuit equivalent, to that shown in Fig. 1A, but redrawn . grid and the cathode were free from loss (leak 3 present a relative phase angle of 180 degrees, ‘ it ispossible by choosing suitable dimensions or values for the inductance existing between the a point corresponding to the screen-grid itself is created, whence neutralization is e?ected. Un der certain circumstances, it may here be per signed for large powers,'the said assumption or? (C1. 179--171) age) and in?nitelyhigh, the screen grid can no longer be considered,‘ as regards high-frequency, to be at cathode potential. However, this means that in the case of the arising of a plate alter nating voltage, there is impressed upon the 40 screen-‘grid an alternating voltage of the same frequency, but: a phase ‘displacement angle of 180 degrees, the amplitude of which’ is' governed by the voltage division due to the capacitance ‘(Cs'A) prevailing between the screen-grid and 4 01 the plate, and the lead inductance (Ls) existing between» the screen-grid and the cathode. In other words, the screen-grid, so iaras the con trol electrode‘is concerned; acts like a further anode or plate; which, to ‘be sure, is subject to ‘alternating voltages" ‘of lower amplitude, but which because ofthe ‘considerable capacitybe tween ‘the screen-gridand the control electrode (Cos) is in‘ rather close coupling relation with the‘ latter. In view of the fact that the alter in a different form; Fig. 2 is a similar form of circuit as shown in Fig. 1B utilizing tubes in 1 push-pull according to the invention; Fig. 3A is _ a modi?cation of the’ arrangement shown in Fig. 1A, but employing grid-circuit neutraliza tion, and Fig. 3B is an equivalent and redrawn circuit. Referring in particular to Fig. 1A, a stage of ampli?cation is shown as comprising a screen gri-d tube V whose cathode is denoted by K, the control grid by G,‘ the screen-grid by S,‘and the plate or anode by A. The plate potential, by ways and means known in the art, is supplied by the aid of a radio frequency choke coil D, while the plate oscillation circuit LCC is relieved of direct voltage by the provision of ‘a blocking capacity B. The radio frequency control voltage is impressed upon the grid circuit across the terminals I] and I. The screen-grid potential is furnished from a source of voltage Else. The in ductances of the'leads or wires brought to the jnating voltages at the plate and the screen-grid ‘ various electrodes, in which‘are ?gured also the 2 2,119,315 leads disposed inside of the vacuum vessel, are indicated in the form of lumped inductances Lo, Ls and LK. According to this invention, neu tralization under conditions independent of fre quency or wave-length is secured by the fact that all of the capacitances existing within the tube as well as the inductances of the leads brought to the different electrodes are simulated; in fact, such simulation, as it were, constitutes a 10 homologous complement of the tube V including all of the leads and wires. The neutralizing action of Fig. 1A may be more readily understood by reference to Fig. 1B. The object of the invention is to arrange the circuit 15 in such a way that regardless of frequency, volt age between output terminals will not produce any voltage between input terminals. This re sult can be achieved by making the entire net work symmetrical in the sense that each of the 20 input terminals has a potential which is inter mediate between the potentials of the output terminals in the same proportion. While not the only way to obtain this result, the simplest way is to duplicate all the impedancesof the 25 tube system (shown in the upper half of the net work of Fig. 1B) by a similar set of impedances (shown in the lower half of Fig. 1B) and which may be called the neutralizing network. In this way it is obvious that the potentials of the input 30 terminals are each half way between the poten tials of the output terminals and since the input terminals have the same potential (in the ab sence of impressed signal voltages) in spite of voltage across the output, the object of the in 35 vention is attained. The inductances serving to simulate the in ductances associated with the tube are charac terized by a supplemental index N (thus: LNG, and LNs), whereas the simulations in regard to 40 capacitance are indicated and designated by NGK (grid-cathode capacitance), NGA (grid-plate capacitance), NsG (screen-grid/control-grid ca pacitance), and NSA (screen-grid/plate capaci tance). Condenser NKA (cathode-plate capaci 45 tance) and NSK (screen-grid/cathode'rcapaci tance) may be omitted, under certain circum stances, provided that inherently low' capaci ties are involved, and that the’waves are not unduly or abnormally short. 50 7 Fig. 113 represents merely the same circuit organization drawn in a different form, with the tube being imagined to be resolved into its ‘con stituent elements. The reference numerals‘ are the same as in Fig. 1A, and the symbols used 55 for the different electrodes of the tube are in the same form as shown in Fig’. 1A. ' For the balance and simulation of the capaci tances‘ and inductances arising inside’ the tube, the use of an inactive tube similar to the tube to 60 be neutralized is particularly well suited. In this respect the several neutralizing capacitances and inductances shown in Figs. IA and 1B may be considered as corresponding to the inter 65 electrode capacitances and lead inductances of the inactive tube. According ‘to the prior art, such tube phantoms‘ have merely been employed for the purpose of allowing of line (circuit) re duction in transmitter stages containing more than one tube by that a working tube was re 70 placed by a phantom corresponding to it. How ever, according to this invention such a simula tion is‘utilized for a different purpose and in a di?erent sense, i. e., with the end in view to se curing neutralization in an ampli?er valve under .75 conditions independent of the frequency. Inasmuch as the simulation of a capacity, under certain circumstances, is more readily feasible than that of an inductance, it may if conditions are appropriate, be feasible to interpose in the leads of the alternating potential applied to the different electrodes, condensers, and to render the resultant impedance (apparent resistance) either ohmic or capacitive. Fig. 2 shows an extension of the arrangement shown in Fig. 1B for a single tube, as applied to H 0 a push-pull arrangement. The reference sym bols referring to the second tube are character ized by primes ('). It will be unnecessary to give further explanations for this circuit dia 15 gram. It is known that the voltages required for such compensation or balancing may be derived either from the grid or from the plate circuit of the stage'in question. Whereas in the case of Figs. 1A and 1B neutralization was effected from the 20 plate end, Figs. 3A and 3B illustrate a circuit or ganization in which neutralization, in a way as known basically from the prior art, is e?ected from the grid. The input circuit of the stage contains the inductance LI as well as the con densers Cl; the output circuit contains the in ductance L and shunt condenser C; the other circuit elements are the same‘ as those used in the preceding ?gures. Fig. 3B shows a modi?ed e representation of the circuit scheme illustrated in Fig. 3A in order that the homologous or mir ror-picture simulation may be made more clearly understandable. ' ' What I claim is:, 1. A circuit arrangement comprising a tube having a cathode, a control'grid, a screen grid electrode within ‘said tube intended to operate at unvarying potential but actually ?uctuating in potential when ‘operated at very high frequen 40 cies due to unavoidable or slight’impedances to high frequencies in 'the circuit between said screen grid electrode and cathode, input and output circuits associated with said tube, and means for counteracting energy transfer from 45 output to input circuits resulting from said ?uc tuating potential, said means comprising a pair of series-connected inductances having their common terminals connected to the tube cathode, an inductance connected to the control grid, the 50 opposite end of said last mentioned inductance being connected to the unconnected terminal of one of the pair of inductances by means of a condenser, said opposite end of said inductance being also connected to the unconnected ter minal of the other inductance’ of the “pair by means of a pair of series-connected condensers. 2. A neutralizing‘ circuit'for an electron dis charge device provided with anode, cathode, con trol grid and screen grid electrodes, comprising a 60 ?rst inductance of a value substantially equal to the self-inductance of the cathode lead having one end connected to the cathode, a ?rst capacity of a value substantially equal to the grid-cath ode capacity having one end connected to the 65 other end of said ?rst inductance, a second in ductance of a value substantially equal to the self-inductance of the screen grid lead having one end connected to the cathode, a second ca pacity of a value substantially equal to the screen 70 grid-anode capacity having one end connected to the other end of 'said second inductance, a third inductance of a value substantially equal to the self-inductance of the control grid lead hav ing one end connected to the control grid and 76. 2,119,315 the other end connected to the other end of the ?rst mentioned capacity, and a third capacity of a value substantially equal to the control grid anode capacity connected between the last men tioned connection and the other end of said sec ond capacity. 3. The circuit according to the invention de ?ned in the preceding claim wherein a capacity of a value substantially equal to the screen grid contrcl grid capacity is connected betweenrthe non-common terminals of the second and third. capacities. 4:. A neutralizing circuit of bridge form for an electron discharge device provided with anode, 15 cathode, control grid and screen grid electrodes, comprising a condenser in the output circuit of said device connected between said anode and cathode, a ?rst inductance of a value substan tially equal to the self-inductance of the control 20 grid lead, a second inductance of a value substan tially equal to the self-inductance of the screen grid lead, a direct connection from one terminal of said ?rst inductance to said control grid lead, a direct connection from one terminal of said 3 second inductance to said cathode, the other terminals of said two inductances being connect ed together through a condenser whose value is equal to the value of the internal capacity be tween said control grid and screen grid electrodes, two serially connected condensers arranged in parallel with respect to said last-named con denser, one of said two serially arranged con densers having a value substantially equal to the value of the internal capacity between said anode and control grid, the other of said two condensers having a value substantially equal to the inter nal capacity between said anode and screen grid, a connection between the junction point of said two condensers and said output circuit, and an inductance and a condenser connected in series between the cathode and said other terminal of the ?rst inductance, said inductance being of a value substantially equal to the self-inductance oi‘ the cathode lead and said condenser being of a value substantially equal to the value of the internal capacity between said control grid and cathode electrodes. WERNER BUSCHBECK.