US2021103A

US2021103A - High frequency amplifier

Info

Publication number: US2021103A
Application number: US650301A
Authority: US
Inventors: Kapteyn Paul
Original assignee: Individual
Current assignee: Individual
Priority date: 1931-02-16
Filing date: 1933-01-05
Publication date: 1935-11-12
Anticipated expiration: 1952-11-12
Also published as: FR731114A

Description

Nov. 12, 1935. P. KAPTEYN 2,021,103

HIGH FREQUENCY AMPLIFIER Original Filed Feb. 2, 1932 Patented Nov. 12, 1935 UNITED STATES PATENT OFFICE.

HIGH FREQUENCY AMPLIFIER Paul Kapteyn, Berlin, Germany ruary 16, 1931 5 Claims.

In high frequency amplifiers it is important, for the purpose of obtaining maximum amplification per stage (aperiodic high frequency amplification) or the greatest possible independence 5, of frequency to employ tubes having the smallest possible capacities between the single electrodes, which do not enter into the oscillation circuit capacity of oscillatory circuits, but are switched in parallel to chokes or resistances. The accomplishment of small capacities is successful to a very considerable degree by the use of screening grid tubes, as in the case of tubes of this nature the reaction of the anode causing in grid circuits the occurrence of the apparent capacity, increased in relation to the static grid anode capacity to the extent of the amplification factor, is capable of being reduced to an ineffective fraction of its normal value.

In itself, however, the inclusion of auxiliary grids is accompanied by the disadvantage that the total of the static capacities is increased. For this reason, generally speaking, the use of screening grid tubes has not heretofore been taken into consideration in the case of aperiodic high frequency amplifiers.

According to the invention amplifier tubes may be used which fulfill to a very extensive degree the above requirements. The invention is based on the recognition that the total of the detrimental capacities of each anode circuit, and accordingly-so far as the tube itself is concerned the total of the electrode capacities efiective between the anode and the cathode, should be kept small.

If now two detrimental capacities are formed by three electrodes, which, for example, are coaxial, whereby the one capacity is naturally formed by the outer and the middle electrode, and the second by the middle and the inner electrode, a certain dimensioning of the middle electrode will exist with given inner and outer electhe inner electrode the radius n, as condition for the lowest total capacity:

5 0 This equation is a result of the following mathematical thinking: The sum of the capacities between three electrodes is where 1 states the length of the condenser. The capacity between anode and controlling grid is very small as a result of the screening effect of the screening grid and can therefore be neglected 10 without noticeable mistakes.

The stated'equation permits of a particularly suitable dimensioning not only in the case of 35 two and three grid tubes in connection with which the same may preferably be made use of, but also in the ease of another quantity of grids.

In the drawing Fig. 1 shows the connection diagram ofa high frequency amplifier according 40 to theinvention,

Fig. 2 a cross section of the tubes used in this amplifier,

Fig. 3 the diagram of another high frequency amplifier,

Fig. 4 a cross section of a tube used in this amplifier,

Fig. 5 the diagram of a high frequency amplifier in connection with an audion and a loud speaker. 5

7 potential to be amplified is applied, for example,

by means of an oscillatory circuit, to the grid G1 of the first stage, so that the grid-cathode ca,- pacity of the first stage enters into the oscillatory circuit. Now the screen grid SGi is preferably disposed as far away as possible from the plate A1, in order to make the detrimental capacity between these two electrodes as small as possible. A relatively large capacity between the screening grid SG1 and the grid Gr does not cause disturbance, because this capacity also enters into the tuning of the oscillatory circuit I.

In Fig. 1 there is furthermore designated by 2 the plate resistance'of the'first stage, by 3 the grid resistance leak of the second stage, and by 4 the connecting coupling condenser. The second stage, the output of which is connected from one plate A2, for example, over a tuned transformer 5, possesses two detrimental capacities, viz., between the cathode K2 and thegrid G2 and between the grid G2 and the screening grid SG2, while the screening grid-platepcapacity. enters into the tuning of the output transformer and accordingly has no detrimental effect. In this arrangement, with .given dimensions of the cathode and the plate the dimensioning of the screening grid will also be of a given nature insofar as the screening grid cannot be approached to morethan a certain extent towards the plate. According to the invention, assuming cylindrical electrodes are employed, it is then preferably,

7 f with a radius Tsg of the screening grid and a radius rk'of the cathode, to so select the radius of the grid Tg that n; is equal to i To the tuned transformer there is connected either an additional high frequency amplifier, a rectifier or another apparatus, which is to be controlled by the high frequency oscillations, for example, a television receiving apparatus or the like.

In Fig. 2, the two systems are illustrated diagrammatically in cross-section. The designations are the same as in Fig. 1. ,1 I

In the case of limited conditions of space, and with very high frequencies, it is frequently impossible to make the detrimental capacities so small that, even when'employing a screening grid, a sufficient degree of amplification is capable of being obtained. desirable to compensate the'small extent of the degree of amplification, necessitated by the impossibility of obtaining a sufficiently large plate resistance, by an appreciable slope. This is accomplished in convenient manner by the use of a' space charge grid. An arrangement of this kind is illustrated in a possible form of embodiment in Figs. 3 and 4. In these figures the same designations have been employed as in Figs. 1 and 2. There is merelythe addition of thespace charge grids RG1 and RG2. The same considerations which were set forth in connection with the above examples are capable of beingapplied also in this case. In the first system there is a single detrimental capacity between the plate A1 and the screening grid SG1, so that the same should be selected as small as possible, while the facts following: 3

In these cases it is.

capacities between the grid G1 and the screening gridSG1 between the gridG1and the space charge grid RG1, and between the space chargegrid RG1 and the cathode K1 are all without detrimental effect, and with the exception of one, 5 enter into the tuning of the oscillatory circuit I. In the second system the capacities without detrimental effect are constituted by the capacity between the screening grid SG2 and the plate A2 and between the'space charge grid RG2 and the 10 adhered to perfectly strictly. The arrangements set forth in the above result in an amplification not obtained heretofore even in the case of certain variation,-also in the case of frequencies at 25 which an effective amplification was hitherto'irnpossible by resistance amplification, 'T l V In the forms of embodiment set forth above the capa'city of two electrodes, which are separated by a third electrode, has not been taken 30 into account'since, more particularly in the case of the narrow grids preferably employed, this capacity as compared with the capacities of electrodes which are not separated by additional electrodes is so small as to be capable of being 35 ignored. 7 r i As already stated above, the invention is important, not only as regards aperiodic high frequency amplifier for particularly high fre- 2,.

quencies, but also in the case of high and low 4i) frequencyemplifiersin which the transmission of greatly varying frequencies is to be ensured in a manner as even as possible, such, for example, as necessary in the case of televisioni'e- 4'5 ceiving apparatus and the like. 7 V

The amplifier system illustrated inFigures '1 to 4, including the coupling elements employedfor connecting purposes, may-convenientlybe arranged in a common vacuum space in the form at, of a multiple tube. r v

As shown by morerecent experiments, it is particularly-desirable. to make the grid cathode .capacity of the first stage larger than in the second stage. The reason for this is based on the l a w y His possible without difificulty in the case of the second stage, which operates with tuned plate circuit, i. e. with a relatively high plate resistance,

.to obtain a very high degree of amplification, 'which may be extended so far that the system cannot be Lmaintainedin anon-oscillating condition. V I i The problem concerned accordingly consists in obtaining the greatest possible total amplification whilst maintaining freedom from oscillation.

Since now the oscillation tendency of the second stage depends, greatly on the loading of its grid and plate circuit, while on the other hand the amplification of the first tube is greatly 'depen'dent on non-capacity of its plate circuit and the following grid circuit,.it is desirable to increase. the amplification of the first system as far as possible by lowering the effective grid-cathode capacity of- -the.second.stage, i.. e. atthe expense "of amplification on the part of the second stagei'ib The amplification of the second stage is particularly diminished by the fact that the greater grid-cathode spacing necessary for lowering the capacity decreases the slope. The small grid cathode spacing of the first stage then required acts only in a favourable manner, as the slope, and accordingly the amplification, of this stage is particularly great. The high capacity which is caused by reason of the small spacing has no detrimental effect insofar as the same enters into the tuning capacity of the input oscillatory circuit.

Particular advantage is furthermore obtained by selecting the diameter of the cathode to be as large as possible, in order to obtain a large emissive surface. Since in this manner the capacity between grid and cathode is naturally considerably increased with the same grid and cathode spacing, merely the first system of the amplifier is, in accordance with the invention, furnished with a cathode of relatively large diameter, while for the second system there is employed a cathode of relatively small diameter.

The invention is described more fully with the assistance of the drawing 5. In this I is an oscillatory circuit, which consists of a coil 1 and a tuning condenser 8, and to which there is supplied the control energy for example by an aerial l2 through the medium of a coil l3. This oscillatory circuit is connected to the grid G1 and the cathode K1 of the first tube of a two-stage amplifier, to the plate A1 of which is fed by the plate potential source Ea via the high resistance 2. The plate is connected through the medium of a condenser 4 with the control grid G2 of the second stage, to

which there is conducted the grid battery Eg via the resistance 3. The cathode of this second system is designated K2. Both cathodes K1 and K2 are heated indirectly by the filaments '9 and H], which may be furnished with heating energy from an A. 0. main through a transformer II. The plate A2 of the second stage is connected to the source Ea via a coil 5 coupled with an oscillatory circuit consisting of the coil 6 and the tuning condenser M which controls a further high frequency tube of any particular kind, or a detector, for example an audion. Between the grids G1 and G2 and the appertaining plates A1 and A2 there are provided screening grids SG1, SGz, which in the known manner are biased with a D. C. potential.

Now according to the subject matter of the 5 present invention, in the first place the capacity between G2 and K2 is to be smaller than that between G1 and K1. According to the additional subject matter of the invention, this is to be accomplished by the fact that the distance be- 10 tween G2 and K2 is made to be greater than between G1 and K1, or the fact that the diameter of K1 is made to be larger than that of K2, other conditions being the same.

I claim:

1. In a high-frequency amplifier two resistance-coupled tubes, each of said tubes having a cathode, a plate and. a control grid, the distance between cathode and control grid in the second tube being larger and therefore the capacity between said electrodes being smaller than in the first tube.

2. In a high frequency amplifier two resistancecoupled tubes, each of said tubes having a cathode, a plate and a control grid, the diameter of the cathode in the second tube and therefore the capacity between cathode and control grid being smaller than in the first tube.

3. In a high-frequency amplifier two. resistance-coupled tubes, the first tube having a screen-grid, the screen-grid-plate capacity being very small, the control-grid-plate capacity of the second tube being smaller than that of the first tube.

4. In a high-frequency amplifier according to claim 3 a resonance-circuit being connected to the control grid of the first tube and another resonance circuit being connected to the plate of the second tube.

5. In a high-frequency amplifier according to claim 3 a resonance-circuit being connected to the control grid of the first tube and another resonance circuit being connected to the plate of the second tube, both tubes together with the coupling-members being mounted in a common vacuum vessel.

PAUL KAPTEYN.