US1875057A - Multiple unit high-frequency amplifier - Google Patents

Description

Aug. 30, 1932. s, LQEwE 1,875,057-

MULTIPLE UNIT HIGH FREQUENCY AMPLIFIER Filed Sept. 17, 1925 4o Fm 46 "g9 22 43 L 49 /n venior:

Patented Aug. so, less srneivrunn LoEwE;

0.? BER-LIE, GERMANY, ASSIGNOE TO RADIO CORPORATION OF AMERICA, A CQRPORA'EEON OF'IDELAWAR-E MULTIPLE UNIT HIGH-FREQUENCY AMPLIFIER Application filed September 17, 1925, Serial No. 56,953, and in Germany September 23, 1924.

It has been found, that the problem of aperiodic high -frequency amplification, where the number of periods exceeds 500,000 per second, becomes with the use of vacuum tubes more and more dificult as the rate of frequency increases (see Barkhausens Elektronenrbhren Leipzig 1923, page 92). For these higlrfrequencies, iowever, it is absolutely necessary to have high frequency amplifiers, because on the one hand, short wave lengths are generally used forbroadcasting purposes, and on the other hand, because short wave lengths have proved especially suitable for long distancetransrnission.

The object of this invention is to provide an aperiodic high-frequency amplifier, which is effective up to very high frequencies. Repeated tests have proved that the ordinary capacity-resistance connection for highefrequency amplifiers is well suited for this purpose, provided two factors have not been left out of consideration, namely the capacities between the circuit elements and the capacities in the interior of the tube should be kept as low as possible. Barkhausen has already pointed out this necessity.

On thevother hand experience has proved that'the resistances. heretofore used for the purpose will cause certain disturbing influences, which render them unsuitable for use in high-frequency amplifiers. They show certain properties, which may be termed residual voltage effects. These properties are characterized bythe fact that as in the case of condensers and storage batteries after a current has passed through such a resistance, a certain residual voltage will remain, and will only very slowly flow 05. It is quite easy to observe this surplus voltage even after. the lapse of several seconds. If a resistance showing these residual properties is traversedby high frequency currents, it will act like a capacity, that is its effective resistance will decrease with the increase of the frequency.-

The problem forming the basis for the in-- frequencies.

1 shall further describe my invention with the aid of the accompanying drawing in which: 7

Figure 1 is a wiring diagram of a three stage amplification system.

Figure 2 is an evacuated vessel in which, according to my invention, most of the three sta e amplification system shown in Figure 1 has been incorporated.

Figure 8 is a modification thereof.

Fig. 1 represents a three-stage high-frequency amplifier produced in conformity with the invention. The tubes used are standard tubes, but without bases. These tubes are indicated by the reference numerals 1, 2 and 8. The heating filaments 4i, 5 and 6 may, for instance be heated in. series by a battery 7. The energy to be ampli lied is applied between the terminal 8 connected to the negative side of filament 4 and the terminal 21 connected to first grid 9. The first anode i0 is connected to the positive pole of a battery 12 by way of a bus for suppl ing positive potential and an ohmic resistance 11 of high resistance value and free of all residual effects. Furthermore the first anode 10 is connected with the grid 18 of the second tube by way of a highly in- Sula-ted condenser 12. The anode 14 of the second valve is also connected, by way of Y the positive and an ohmic resistance having a high resistance value and being free are further connected, by way of a bus for stage is similarly connected to the third.

supplying negative potential and like resistances 18 and 19, with the negative battery pole. The first tube or stage is connected. to

the second by an impedance coupling com-' prising the high resistances'll and '18, and the condenser 12, and the second tube or The amplified high-frequency voltage may thus be taken off between the terminals It is possible, for instance, toconnect a tuned frame antenna between the terminals 8 and 21, and also by inserting a coil or other suit 1 able. coupling means between the terminals 20',ithe amplified high frequency voltage may be appliedto a' vacuum tube detector or crystal detector circuit followed by one or morestages of low-frequency amplification. It has .been'found, that it is possible with the help. of such resistances,-whic'h are free of any residual efifect in the anode circuit, as well as 1n the grid connections, and bytWOlfling 'the' production of-capaclties 1n the tube base, tofproduce properly operating highfrequency amplifiers up to wave lengths of 150 meters. I

, The high-frequency amplifier described above will still possess a comparativelylarge capacity between the several elements of the circuit. {In orderto reducethis capacity to a 'minimunnthe following steps have been taken by the inventor H The multiple high-frequency amplifier system is enclosed within a tube, the resist ances in the grid circuit and the transfer capacities being also preferably mounted withinsaid tube. For this purpose, the resistances in the grid circuit and the capacities 12 and 16' can be enclosed in special tubes, or if necessary in vacuum tubes.

Fig.2 shows as an example atriple or three stage amplifier, constructed according to this invention. I

In a glass frame 22 the filament 24 adapted to be heated to incandesence is held in position by the insertion of a tungsten spring 23. Thethree grid and anode sets constitutin g the three stages are, as shown in this figurefarranged either on the side, or cylin drically round the glowing filament. On the framethere is further mounteda collecting wire or negative bus 25,.connected with the negative pole of the heated filament. Similarly the frame carries a rod or positive bus 26' connected with the'positive battery pole;

The first grid is carried, for instance, through the glassbulb at 27 and the positive terrninal of the filament iscarried through at 28.

The first anode is'connected by a resistance 11, which is free of residual effects, to the positive collecting wire or bus, and by Way ofa capacity 12 which is preferably enclosed within an air-tight space to the second grid 13. The second grid, if desired, can

also be connected by Way of a resistance 18,

which'is absolutely free of residual effects,

to the negative collecting wire. The second a condensor 16 which is enclosed in ava'cuuin to the third grid 17. The third anode is led out through the stem, while the third 'grid;

can-be connected by way of a resistance 19 of the same character to the negative collecting wire 25. The surrounding glass bulb 29 encloses the whole apparatus airtight and it has altogether five sealing-in points,-viz.,

two for the filament ends, one for'the' first L gridyone for the third'anode, and one-for the positive collecting wire'or' bus. By means j of this arrangement, it. is possible to reduce theeffect of the injurious capacities tosuchi an extent that amplification of high'frequen-j cies up to 10,000,000cycles" can be'obtained,

further improvementcan be obtained by f the use of insulated" grids. By the use'of] such grids, that is, a grid thesurfaceof? which is suitably screened against the reg ception 'offelectrons, as for instance by the interposition of mica sheets or by coating the grid with borax or porcelain. enamel, the. otherwise necessary blockcondensers 12' and 16 can bedispensedwith, as well as the re sistances 18 and 19 in the grid circuits which, 1

are necessary in most cases.

An example of the construction of the sys} term with insulated gridsfis shown in FigI'Si' The grids in this case are designed as control electrodes, and are not fixed between; plate and cathode, .but beyond the spacelbe-Q tween plate and cathode.

are well known. mounted as shownin Fig; 2. The'first anod The effect and principles of this arrangement as amplifier The heating filament is,

40fissituated in the left hand top corner, and. the first control. grid 41 in the right hand} topcorner'; Itis carried out of the glass bulb just like'the filament terminals. Mica plates are interposed between each of the con- I J trol electrodes and the filament, said plates being either, fastenedlon to the control electrodes, or kept freely in suspension by means of small brackets positioned in the space be-I tweenfilament andcontr'ol electrode. For

the three stage'sithese mica plates-are designated respectively 42, 43, 44. Fromthe-first anode the circuit leads by way of a=resist= ance 45 which is free from residualefiectsi 1 to the'positiv'e collecting wire 26', which is also sealed into the 'foot" of' the bulb. The

second stage is so arranged that the sec d i A control grid 46 is situated on the same-sideas the first anode.

It is connected with the latter by means of a wire, but screened from the filament by an interposed mica plate .43. The second anode 4:7 is connected, by Way of a resistance 48, free of residual effects, to the positive collecting wire 26. The third control grid i9 is placed on the same side of the filament as the second anode and this grid is also screened from the filament by an interposed mica plate 44, and connected conductively with the second anode by a wire. The third anode is separately supported and led out through the stem of the glass bulb.

In the manner described it will be possible to build high-frequency amplifying sets, hardly larger than the plain amplifying tubes used at present, and yet many times more effective.

.My means of the last-described construction an efiective amplification of the highest existing frequencies will be made possible. It is of course not necessary to confine oneself to a three stage construction, since a still larger number of similarly constructed stages may be used.

It is further of great importance that the first stages have comparatively short lengths of the anode and the grid, as the currents in the first amplifying stages are very weak. Only the subsequent stages have larger anode and control surfaces to correspond with the increase of the currents to be carried by the apparatus.

Frequently the problem may arise to construct such sets in a form which will permit of a low current consumption. If filaments are used which are coated with an oxide covering, there will be no difference in the design used for tungsten filaments.

If, however, an economy in heating current by the atomization of magnesium or similar metals in vacuum is desired, care must be taken that the deposits of metal thus produced will not provide any conductive path between the different parts, which should be insulated from each other. The inventor has found that the formation of a conductive deposit between two points which should be kept insulated from each other can be avoided by protecting the points in question by means of a screen either of glass, metal, or mica, which is placed in front of the places to be protected against such deposits. Protective screens of this kind are used wherever it is necessary to maintain a high insulation. The deposit in this case settles on the screen, and the protected parts, which must remain insulated, will remain free of such deposits. The evacuation of these systems is best done by placing the entire tube on the pump in a high frequency eddy cur rent field.

For mounting the blocking condensers in the vacuumtubes according to Fig. 2, it. will.

be preferable to enclose the condensers separately in airtight glass tubes. This method.

evacuate the condenser itself. For example,

two copper foils separated by a strip of mica may be placed within a glass tube, said foils I being rolled into a small coil. The two ends of the glass tube must be sealed, and the two leads carried out-side. This tube may be freed of air, but it is quite sufficient to seal in the condenser perfectly airtight. Similarly, the degassing of the high ohmic resistances may be dispensed with by sealing them, if possible, under vacuum, into glass tubes. Condensers, or resistances, enclosed in a vacuum tube in the manner described above will behave exactly like any parts of the surrounding glass surface, considered from a vacuum-technical point of view.

I claim:

1. A. vacuum tube adapted for multistage amplification, comprising an evacuated envelope, a plurality of stages contained therein, a single filament common to all the stages, a control electrode and a plate electrode for each stage, impedance coupling between successive stages, a collecting element, and a high resistance element connecting the control electrode of the last stage with the collecting element.

2. A vacuum tube amplifier, comprising an evacuated envelope, a plurality of stages contained therein, a single filament common to all the stages, a control electrode and a plate electrode for each stage, a blocking condenser between each grid and the plate of the preceding stage, a conducting element within the tube, a high resistance element connecting each plate with said conducting element, all of said elements mounted entirely within the tube, and external leads for the filament, conductor, first control electrode and the last plate.

3. A vacuum tube adapted for multi-stage amplification, comprising an evacuated envelope, a plurality of stages contained therein, a control electrode and a plate electrode for each stage and a common filament for all the stages, a bus adapted to supply positive potential to the plates, a high resistance element connecting each plate with said bus, a condenser connecting each grid with the plate of the preceding stage, a bus adapted to supply negative potential, a high resistance element connecting the control electrode of the last stage with the said last named bus, all of said elements being mounted entirely w thin the tube, and external leads for the filament, first control electrode, last plate and said buses.

4. A multistage vacuum tube amplifier, comprising an evacuated envelope; a plurality of resistance-coupled stages wholly contained Within said envelope, at common cathode for all said stages, grid and plate electrodes for each of the stages, external con- 7 necti'ons to both terminals of the-common cathode, an externaliconnection tothe grid electrode of the first stage, another external 7 connection common to the grid electrodes of thesucceeding stages, an external connection to the'plate electrode of the last stage, and

another external connection common to the plate electrodes of the remaining stages.

In testimony whereof I have affixed my signaturel SIEGMUND LOEWE.

at L.

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