US2015185A - Electron tube circuit scheme - Google Patents

Description

Sept. 24, 1935. G. JoBsT ELECTRON TUBE CIRCUIT SCHEME Filed June 2, 1933 ELA l G J T Patented Sept. 24, 1935 UNITEDl STATES mais PATENT ortica 2,015,185 ELECTRON TUBE CIRCUIT SCHEME Gunther Jobst, Berlin, Germany, assignor to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application June 2, 1933, Serial No. 674,048 In Germany February 11, 1932 7 claims. (c1. 179-171)v The invention is concerned with a circuit ari rangement for electron tubes comprising more than two grids, the characteristic feature of which resides in the fact that two. or more grid-like electrodes located between Ythe .heated cathode and the control grid are maintained at a constant, preferably positive, potential.. By the agency of these the emission current, in the presence of a stabilized cathode temperature, is regulated as regards density and velocity. By proper choice of the voltages it is possible to insure such a distribution of the current that inside the discharge space there is setup a surface of zero potential. This surface may be regarded as the place or locus of a virtual cathode which behaves in reference to the control element in the very same way as a real cathode. Owing to the fact that the said virtual cathode is provided in the direct vicinity of the control grid, the controllability of the tube is considerably enhanceable, indeed, this is the actual purpose ofv the invention. For the electrode system comprising the heated cathode and the electrodes serving for the object of regulating the density of the electrons as well as thevelocity thereof, there is here suggested the use of the term regulator cathode. For a still better and clearer comprehension of the scheme disclosed the following additional explanations may not be amiss.

The electrons escape or issue from normal hot cathodes practically at zero speed. As a result the electrons are able to reach electrodes only when possessing a potential that is positive in reference to the cathode. The discharge process f in space-chargefgrid type of tubes may be so conceived that the space-charge grid does not represent anything else than acathode whence the electrons escape at a certain rate of velocity corresponding to the potential of the space-charge grid.

Now, the present invention is predicated upon this point that it is of essential advantage toY make the regulation of the number and the speed of the electrons passing through the space-charge grid independent of each other, and this is an objective inattainable merely by Variation of the space-charge grid potential. In `the presence of only one grid, disregarding the chance of regulat- Ying the emission from the cathode by altering the temperature thereof, current and velocity are always fixed by a relation governed by the geo-'- metric disposition of the grid and the chosen voltage.V For a better understanding of the invention reference is made to the accompanying drawing, in which: Y

' Fig. l shows a diagrammatic circuitarrangement of an electron discharge amplier embodying the invention;

Figs. 21u25` and 2c show the relationship betweenthe grid and plate currents of the arrangement of Fig. l,

Fig. 3 is another schematic circuit diagram an amplier embodying the invention,

Figs. 4 and 5 show characteristic curves of the amplier arrangement of Fig. 3 and, C

Fig. 6 shows in a typical case the relative voltages between the several tube elements in an ampliiier embodying the invention.

However, what advantages'are offered by the chance of separate regulation of current and electron speed shall be demonstrated by the following example:

' Referring to Figure l, inside avacuum vessel, opposite a regulator or cathode comprising a heated cathode K and the two space-charge grids R1 and R2 is placed a grid G and in the rear thereof a plate A, both of these, for instance, being at positive ,voltages in reference to R2. The plate potential EA and the grid potential EG are stabilized in reference to R2, and by means of suitable adjustment of the voltages of the electrodes constituting the regulator cathode, the aggregate current JA-i-JG cwing to the electrodes G and A is stabilized by that the voltages E2 and E1 prevailing between the grid R2 and the grid R1 in reference to the hot cathode K are adapted to each other in a convenient manner. The total current JA-l-JG being the same as to value or size may then be altered as regards electron velocity and current density. In the presence of a stabilized or constant aggregate current, the Ydistribution of the partial currents JG and JA, that is to say, the relation as the current density drops,- and that incidental-V ly space-charges are developed between plate and grid which can no longer be overcome by slow electrons so that the current is directed toward the grid.

Now, it is these circumstances that may be utilized to advantage for the control of electronic or thermionic tubes, seeing that the accumulating space-charge is influenceable with extremely great ease where the densities are large, the control sensitivity growing when the electron density is raised at a denite relationship in reference to the electron speed.

Regulating the potential conditions so that at constant speed of passage or flow of the electrons through the grid R2 the aggregate current to the plate increases, with a grid G mounted ahead of the plate A being negatively biased so that it will carry no current (see Figure 3), then there results for the current JA as a function of the voltsage E1 between hot filament K and the grid R1 a relationship as shown graphically in Figure 4 where the voltages Eo of the grid G are given as parameters. For one or these curves in each case the speed of -llow of theA electrons across R2 as well as grid and plate potential is constant; while from one curve to the next the negative biasing voltage of the grid EG changes. It will be seen from these graphs that the influence oi variation of EG at the points of most vmarked droop of JA is by far the greatest.

In other words,

SUA dEg which is equivalent and tantamount to the regulability of control of plate current, is a function of E1 (current density p and is maximum on the drooping branch of the curve JA.

It may be said, however, that furthermore the droop of the JA curves and thus the controllability are caused to grow further if E2 is raised and if E1 correspondingly is so adjusted that JA cornes to lie in the steepest portion of the drooping curve (see Figure 5). In Figure 5 Eo is not altered for the two branches of the curve; in fact, the curves distinguish Vthemselves from one another merely by dissimilar rates of speed of passage across "ie grid R2, and in each instance, there is a critical value for E1 so as to adjust conditions to maximum or optimum controllability.

The invention consists in that in a circuit scheme comprising electron tubes, that is to say, electron tubes of the space-charge grid type, Ways and means are created whereby the critical speed may be adjusted to attain maximum controllability no matter what the current density (that is to say, for all current densities).

According to the invention, tubes of a kind provided with more than two grids are employed in this manner that the two grids located at closest proximity to the cathode are kept at a constant, preferably positive, potential in reference to the cathode, while another consecutive grid serves as the controlling means or grid. The positive potentials impressed upon the said two constant grids are preferably regulable as by adjustment of the voltages of the batteries E1 and E2 of Figs. 1 and 3. But the positive potential of the second grid is most conveniently chosen higher than that of the first grid. The control grid most advantageously is operated at a biasing potential that is negative in reference to the grid adjacent thereto in the direction of the cathode, to be more precise, in such a way that the negative biasing voltage of the control grid in reference to the grid adjacent thereto in the direction of the cathode is approximately equal to, or somewhat higher than, the voltage thereof.' In other words, the control grid voltage is negative with respect to the cahtode, as shown in Figure 3. It is both feasible to ground the grid at closest proximity to it on the side of the cathode as well as to ground also the cathode itself.

Figure 6 illustrates the distribution of the potentials inside a tube with regulator cathode both in respect of the voltages referred to the electron issue point of the regulator cathode being the zero point as well as where the Zero point is referred to the hot filament.

It has been shown that tubes with regulator cathode tend toward instability, especially where the regulator cathode exhibits a high internal resistance. To remedy this condition it is here fu;- ther suggested to provide between the accelerator grid R2 and the heated filament means adapted to suppress stray oscillations and consisting, e. g. of leaky condensers.

Of course, the regulation ofthe electron density and of their acceleration should, as far as feasible, be independent of each other and free from reactions. This is realizable by the aid of a screen electrode i@ mounted between R1 the current regulating grid, and the velocity regulating grid R2. The said electrode is operated at a xed voltage which is lower than that of the accelerator grid and which, indeed, is preferably chosen equal to the cathode voltage. What is most convenient in this connection is to keep the grid being the second one gured from the cathode at cathode potential.

It has been pointed out above that the controllability grows approximately in accordance with a linear law with Variation of E2. The increase in controlling power by raising E2, for instance, is merely limited by the load capacity of their amiliary electrode which is called upon to carry increasingly larger currents as the voltage increases. In the same Way as the controllability is acted upon and inluenced by Ez will the same power be aiected by EA. However, the influence of EA should be kept low by choosing suitable dimensions therefor, seeing that under actual operating or service conditions the plate circuit contains also the useful resistance Ra, and since reaction of EA must be precluded as -far as feasible for reasons of amplification.

In lieu of G recourse could be had also to magnetic action exercised from a field E located at right angles to the trajectory of the electrons; f

and in order that the controlling action exercised by means of the grid G may be rendered as intense as feasible, the voltages should be so adjusted that, in the presence of given positive voltages E2 and EA the plate current JA by suitable choice of the aggregate current comes to lie upon the drooping branch of the plate current curve. Incidentally the control action grows with growing value of E2, whereas the iniiuence of EA should be precluded as far as feasible by choosing suitable dimensions for the tube, for instance, by the provision of a screen grid l i, which Vmay be maintained at a constant voltage by a battery I2.

Due to the steep slopes of the characteristics of these tubes, excellent amplification is obtainable and the application of such tubes tends to reduce the number of amplifying stages. The particularly steep slopes may also be of great importance when serving as high frequency ampliers or as rectiers and also where it is desired to obtain a great variation in amplification eventually by controlling the bias. No difliculty exists in distorting characteristics by means of control cathode tubes in such manner that they present very extended end curves similar to the characteristics of tubes thus making possible a smooth variation without incurring distortion. In like manner such tubes can also be used as anode rectifiers or as audion stages.

The Aadvantages described above also enable the use of this` tube in ultra short wave work in Y theplace of the ordinary scree'n grid tube. Due

to the steep slope obtainable with such tubes, the excitation of the oscillations is made possible also in case of shortest waves and in oscillating circuits of relatively small impedance at which other tubes would then not function.

If desired, a tube as described may be used for frequency modulation as a variable resistor.

. These tubes, when used in these circuits, present the advantage that the condition of the inner impedance thereof can be conveniently and effectively varied by means of varying the potentials of one of the auxiliary grids, for example, a density grid.

In transmitting Vcircuits these tubes can be used as transmitter tubes for a natural or separateexcitation. Due to theirgreat capability of controlling, these tubes possess only low zero voltages so that the anode potentials present can be utilized to a great extent and thus are not wasted, whereas in ordinary tubes a large part of the anode potential is lost due to the high Zero voltages.

Thus the control cathode tubes are particularly suitable for operation with anode potentials which are small in comparison with anode current. It has been found Ythat for operating control cathode tubes as transmitting tubes with natural or separate excitation a proportion of power to anode potential greater than 1 watt l 10 volt 10 amperes is particularly favorable. Y

I claim:

l. A circuit arrangement comprising a vacuum tube having a cathode, a plate, a first grid located adjacent said cathode and arranged to regulate the number of electrons emanating from saidcathode, means for applying a positive potential to said grid, a second grid located between said rst named grid .and said anode, means for applying a constant positive potential to said second grid which is greater than that applied to said first grid whereby said second grid controls the velocity of the electrons passing through said first grid, a signal control grid located .adjacent said plate, and means connected to said control grid arranged to apply a negative bias voltage thereto, the means for applying a Vsaid first grid, a. second grid located between said first grid and anode, means connected to said second grid for applying a steady positive potential thereto which is greater than that applied to said first grid, means to prevent reaction between said first and second named grids, a control grid located between said second grid and anode, means for applying a steady negative potential to said control grid, and means for applying a positive potential to said anode. Y

4. A circuit arrangement comprising a vacuum tube having a cathode, an' anode, a first grid located between said cathode and anode, means for applying a positive potential to said grid, a second grid located between said rst grid and anode, meansfor applying a'constant positive potential to said second grid which is greater than that applied to said first grid, and means for applying a positive potential to said anode which is at least twice that of said secondkgrid whereby an increase in the potential applied to said first grid causes a decrease in the current passing to said anode.

5. A circuit arrangement comprising a vacuum tube having a cathode and anode, a. first grid located between said cathode and anode, means for applying a steady positive potential to said grid, .a second grid positioned between said first gridY and anode, means for applying a positive potential to said second grid which is greater than that applied to said first grid, a control gridV Ya vacuum tube having a cathode and anode, a

first grid located between said cathode and anode, means for applying a positive potential to said grid, a signal control grid located between said rst grid and anode, means for applying a negative bias of variable amount to said signal control grid to thereby control the current flowing to said plate, a third grid located between said rst and signal control grids and means for applying a steady positive voltage to said third grid which is independent of voltage variations of said signal control grid and of such value .as to fornr a surface of zeroV potential immediately adjacent to said signal control grid.

'7. The combination defined in the preceding claim in which an additional grid is located between said rst and third grids to thereby pre- Vent reaction of said third grid on the electron stream between said cathode and first grid.

GNTHER J OBST.

Images