US1673287A - Electron-discharge-tube amplifier system - Google Patents

Description

Patented June 12, 19 28.

IPATENTPOFFICE- LESTER. L. JONES, or ORADELL, NEW I Z ELECTBON-DISCHARGE-TULBE AMPLIFIER sYsmnu.

' v Application fllediJnne 11, 1927. Serial No. 198,061.

This invention relates to an electron dis charge tube amplifier system; and has special reference to the provision of a non-tunable amplifier system especially adapted for use in the amplification'of high radio frequencies and having a high amplification over a relativel wide wave length band.

The prime 0 ject of my present-invention centers about the production of a system of amplifying high, such as radio ferquency vibrations, by meansofelectron tube or re-' lay circuits havin fixed or non-adjustable constants, which unctions to produce high and efiicient amplification over a considerable or relatively wide wave length range or bandi Amplifier systems in which the circuit constants (capacity, inductance and resistance of the circuit) are fixed and non-adjustable are known in the .prior art as untuned .am'

plifiers, and are characterized by the lack of uniformity in amplification, together with the great inefficiency of amplification in some part of the frequency band. This objection:

able characteristic is due ,to the fact that the amplification 5 of such systems varies -'with the frequency impressed upon the system, the

maximum amplification being produced at, the resonant frequency of the system. One of f the important principles of mypresent invention resides in the production of electron discharge tube amplifier systems of this char acter, that'i's, embodying fixed or non-vari able circuit constants, constructed and designed however so that in lieu of producing an untuned system, there is produced a circuit arrangement or system which isselftuning or is automatically tuned over a" relatively wide wave length band resulting invthe' obtaining'of a uniformly hi h amplication over said wide wave length and.

The principal object of the invention may therefore be said to relate more specifically to the production of a high and reasonably constant degree of amplification over a band such as, for example, a range of .from 500 to 1500 kilocycles in circuits employing the electron discharge tube relay, which circuits have fixed constants or circuit adjustments of inductance, capacity and reslstanc'e. Frorn another aspect, the application of the principlesof my present invention'results in the transformation of a so-called untuned amplifier into an automatically tunable amplifier, qr

an amplifier which is self-tunable over the wave length band to produce uniformly high and elficient amplification over the band.

The principles of my present invention are applied in their preferred form to a triode or electron discharge device or tube-having grid, late and filament electrodes, the said tube orming the couplin means between an input circuit having xed circuit constants and an out ut circuit also having fixed constants. Broa ly considered, 1' have discovered that the contants of both the input and output circuits of said .triodeI'may be so predetermined and inter-related as to cause the input circuit to resonate or maintain its resonance at frequencies over; the wave length band or a considerable portion of the wave length band for which the systein is designed, such bandbeing, for example, the broadcast band of frequencies now in use. a Considered in its more specific aspects,'I have discovered:

capacity, inductance and resistance, of the input circuitof the triode may be so fixed that the production of a predetermined variation with frequency in the input capaoityrof the triode or tube over a given wave length band, maintains the said input circuit resonant oversaid given wave leii th band, and

That the constants of t e output circuit may be so fixed orpredetermined. as to be effective with the change in frequency over said Wave length band for producing that predetermined variation in the tube input capacity which results in the said maintaining of the input circuit resonant over saidwave length band. s

Bythus predetermining the constants of the input and output circuits and predetermining this relation therebetween, the

circuit system, although devoid of variable or adjustable tuning elements such as are commonly employed in the priorart in tunable systems, is made to resonate for any selected frequency over a wide frequency range,

To the accomplishment ofv the foregoing and such other objects as will hereinafter appear, my invention consists in the elements and their relatlon'one to the other, asvhere- (1) That the constants, that is to say,,the

inafter more particularly described and sought to be defined in the claims; reference being had to the accompanying drawings input circuit thereof to resonate at the frequencies. over the band frequencies,

Fig.3 is a graph showing the difference in amplification curves between an untuned system of the prior art and an automatically tuned system of my present invention,

Fig. 4 is a graph showing the effect pro-. duced on the input capacity of thetube or triode by the predetermining of the con stants of the output circuit. and

.Figs. 5 and 5 are graphs depicting the manner of inter-relating the characteristics or behaviours of the input and output 'cir 'cuits so as to produce the amplification efficiency desired over the wave length band. Referring now more in detail to the drawings, and having reference first to Fig. 1 thereof,I show myinvention applied to a cascaded electron discharge tubesystem having an,

electrondischargetube V1 forming the coupling means between an input network I and an output'network O, the said input network embodying a transformer T1 which it is desired to keep in resonance with all the frequencies over a given wave length band,

' andthe output circuit 0 including a transfixed or made invariable.

former T2; .the constants of said input and output circuits- I and 0 respectively being The input circuit I is shown as a radio frequency input coming from an electron dischargetube V0 which may be another amplifier tube connected to any desired means for selecting a particular frequency over a: given frequency range; and the output circuit O is shown connected to an output, asfor example to "an electron discharge tube V2 operating as a detector, which inturn has output terminals designated output which may be connected to the usual phones or to an audio amplifier network. Each of the electron discharge devices comprises a three-electrode tube having a grid-g, plate 12 and filament f.

The detector tube V2 may beprovided with the grid leak or integrating device g] and the various input andoutput terminals are connected in a manner well known to the art to the A and B batteries or equivalent sources of energy designated as A, A+ and B+.

In this circuit system'of'Fig. 1, the input circuit 1, and more specifically the transformer-T1, is desired to be kept in resonance with all of the frequencies selected by the lowing circuit network preceding the inputI over the desired wave length range. In accordance with my invention, to hold this reso- I This total capacity I show in phantom or dotted line in Fig. 1 of the drawings as.C, the same being shown as variable since this capacity (lmnst be varied to maintain the resonant condition. This total capacity is made up of a fixed amount corresponding to the distributed capacity of the primary and secondary coils p and a of the transformer T1, the. plate to grid and filament capacity of the preceding tube VO, the connections from the. transformer T1 to the grid and plate of both tubes V0 and V1, and the grid filament capacity of the tube V1 (this is all fixed) and a variable amount which is the grid-plate capacity of the tube V1. This total capacity is denoted and will be referred to herein as the tube input capacity. This variable grid-plate capacity is a function of the frequencyand of the output load (the transformer T2 and the folcircuits connected thereto). In order to maintain the-resonance of the input circuit I or the transformer T1, the tube input capacity C must increase with decreasing frequency,

This requirement of the characteristics of the input circuit to maintain resonance is shown by the graph in Fig. 2' of the drawings, in which the ordinates represent the resonant wave lengths of the transformer T1 and the ab'scissae represent the capacities which will keep this transformer resonantat the various frequencies. In this graph the curve abc represents the performance of the transformer T1, which transformer is designed to have a natural-wave length at about 205 meters. The full line portion be of the curve shows the 'performance of the transformer beginning with the wave length at which the transformer oscillates when shunted with a total capacity of approximately 30 mmfds; and the dotted part ab of the curve is an exterpolation for determining the minimum capacity of the inputcircuit. This value of minimum capacity corresponds to the lowest values of the tube and transformer coil capacities that can be securedwith good engineering design and present-day reliable commercial llu amplifier tubes. The curve shows how much As aforestated, I have discovered that this variation in the tube input capacity may be obtained by selecting the characteristics of the output circuitconstants. The desired increase or variation of the'tube input ca pacity C is supplied by'an increase of the grid-plate capacity of the tube V1, which increase is secured by selecting a transformer T2 having constants which are effective with the change in frequency over-the wavelength band for producing the desired variation of the tube input capacity over the said wave length band.

The factors which governgthe selection of the characteristics. of the transformer T2 ,are determined from the behaviour of the transformer has no leakage inductance and is therefore in the nature of a simple. in-

ductance. The form of the tube input ca- -pacity curve is similar to the resonance curve of the transformer as shown in Fig. 4 of the drawings. wherein .IS depicted curves of transformers, the' ordinates ofthe graph of Fig. 4 representing the added input capacities (C) and the abscissae representing the impressed wave length.

The curve B B of the graph of Fig. 4 shows the variation in the input capacity produced in the tube V1 when the same is followed by a transformer which I designate as a bifilar transformer, to be described hereinafter, having a resonant Wave length of approximately 400 meters (with a total capacity across it'of 3O mmfds.). Curve A-A on'the graph of Fig. 4 shows the variation in tube capacity of the tube V1 produced by a transformer T2 in "which the coils are placed exceedingly close together, separated only by thin mica sheets. This transformer has a slightly higher natural wave length, but the form of the curves A-A and- B-Bis the same. It will be noted that there is an increase of tube input capacity from 10 mmfds. at 100 meters to approximately mmfds. at 400 meters; As

. will be shown hereinafter, the self or automatic tuning of the transformer T1 is accomplished by the rising tube input capacity corresponding to that section of the curves at the left of the peak thereof.

It. willnow be apparent from a comparison of Figs. 4 and 2 that the characteristics of the transformer T2 fol-producing the input capacity change with frequency may be so selected as to coincide with the characteristics of the input circuit Ortransformer T1 of producing the resonance over the wave length range bythe variation of the input capacity C. This is shown inLFigs. 5 and 5 Fig. 5 showing thecurve of Fig. 2 with the wave lengths as the abscissae and-the change in capacity across the transformer-T1,

as the ordinates, and Fig. 5" showing the..

curveof -Fig. 4 designed so as tohave a" component or sectionggat the left ofthe peak thereof which may bemade to coincidewith the-curve of Figh I have foundby empirical determinatlon that these curves may be made to coincidebyzasuitably selecting thecharacteristics of the? fixed constants of the transformers T1 and".

given selective characteristics of the transformer T1, I select the characteristics of the transformer-T2 firstly with respect to the rate change of tube input capacity, and secondly with. respect to the frequency corre-" T2. To accomplishthe desired end, with 'sponding to theminimum and maximum I of the tube input capacity. The desirable rate change of tube input capacit is basically determined by a curve suc shown in Fig. 5; and this is, determined mainly by the physical form of the transas that former T2, and more specifically by the dis-v f tributed capacity of the coils thereof and tween the primary ands thereof.

leakage, the slower the variationof tube in- ['90 more especially by the magnetic leakage beand secondary coils p. s a general principleit may be stated that' the less the magnetic put capacity with frequency, and the lower the distributed capacity ofthe transformer,

the greater therelative magnitude of the tube input capacity change. "The minimum andmaximum points of the curve of Fig. 5",.that is, the second characteristic .of the transformer T2, ,is determined for an physical form of transformer by suitably selecting the inductance of the windings so that' the said transformer T2 has a natural frequency corresponding to the lowest frevquency of the wavelength band. Thus, if"

the wave length band is 1500 to 500 kilo-' cycles, the natural frequency of the transformer T2 would be selected to be slightly ,lower than 500 kilocycles, as for example.

470 kilocycles This natural fre uency of the transformer T2 is selected iii-this wise,

because at this natural frequency of the transformer T2, the tube input capacity of.

the tube V1 is a maximum, as shown by the curve of Fig. 5 and the maximum tubeinput capacity is necessary'in order to maintain the preceding transformer T1 resonant to this lower frequency, as shown by the curve.

of Fig. 5 of the drawings.

is secured by arranging the trans-former structure to create a similar form of equivalent resistance. This problem may also be attacked by arbitrarily changing the fixed alueof capacity across the transformer T1 Decrease in capacity of the required form at the higher end of the frequency band.

If, for-example, additional capacity is added to T1, then a larger variation of the tube input capacity will tune, over a narrower frefrom leakage inductance to avoid-points of inflection in the tube'input capacity curve,

7 and second, relatively low distributed capacw Since then transformer ity to insure a relatively slow rate of change t ube inputcapacity with frequency.

V structures are broadly tuned by this, that is, the change in response with frequency change is smalh it is not necessary to have the terminal capacity 'exactly correct. A deviation of 10% or '20%in the' actual capacity from that which is theoretically required would produce only 5% deviation in the resonant frequency from the impressed frequency. This change in response due to a frequency change would be relatively small so that the sacrifice in efficiency due to'lack of coinqidence of these curves is very small. It is.

only necessary that the curves of Figs. 5'"

and 5 have approximately the same starting and ending points and that their form in between these points-be generally similar.

The preferred method of obtaining the minimum distributed capacity and minimum I leakage inductance of the transformers T1 and T2 will now be described. Minimum distributed capacity is generally desirable for two reasons first, because. a small capac ity across a transformer at radio frequencies tends to increase the voltage obtainable, and second, because the minimum capacity'extends the frequency band over which automatio tuning may be secured, since this band is dependent upon the initial capacity. The minimum leakage inductance is desirable firstly, to secure the maximum induced voltage in the secondary of the transformer, and secondly, to eliminate the second or. short wave mode of oscillation of the transformer. I have found that to produce this minimum distributed capacity and minimum'leakage inductance the transformer should be wound bifilarly as disclosed in my copending appli-v plate-voltage supply and the filament connection of the tube. The bifilar winding is preferably random wound in-a relatively narrow slot so as to yield a coil of relatively small distributed capacity and of relatively high inductance, the inductance being made su ciently great to give anatural frequency to '-the transformer in connected circuit corresponding to the lowest frequency of the wave length band for which the system L is designed. v

Preferably both. of the transformers T1 and T2 are bifilar transformers. having similar characteristics, the inductance of the transformer T2 being however higher than T1 so thatthe natural frequency. of the transformer T2 is generally lower than the natural frequencypf the transformer T1. This produces an increase oftube input capacity from the higher frequencies to the lower frequencies corresponding to the hatural frequency of the transformer T2.

As an example of the application of my invention I shall assume that the relay tubes have amplification constants of 8, grid plate capacities of '10 mmfdsand grid filament and plate filament capacities of approx mately 10 mmfds. The total capacity hanging into a transformer such' as T1 would therefore be of'the order of 30 mmfds.- T o resonate at about 200. meters this transformer a T1 should have an inductance of about 360 microhenrys. This is where the transformer has substantially zero leakage, asin the case of the bifilar type. has substantial leakage the. computation of its long wave natural frequency is more difficult, and it is best to adjust the transformer experimentally to the desired natural frequency. In such a system the transformer T2 shouldhave an inductance of approximately 23 millihenrys so as to resonate at about 600 ,kilocycles. f The tube input capacity of the vacuum tube V1 would then increase by approximatelyTO mmfds.

at thislow frequency so that the preceding transformer would be resonant to about 800 kilocycles whentheimp'ressed frequency is 600 kilocycles, producing a substantial coinciding of resonance. More exact matching of the transformer resonance with the fre-- quency may be secured by the use of either 'tubes having lower grid filament and plate filament capacities or by the use of tubes having a higher amplification constant.

It is seen therefore that the first transformer T1 is preferably arranged to have a natural of'1500 kilocycles so that it is resonant at 200 meters when the tube input capacity is a minimum. The ube input Where the transformer ioo' capacity -is a minimum at 200 meters because this frequency is so far removed from the frequency of the transformer T2 that transformer T2 causes a very slight change of the tube input capacity from the normal minia the natural frequency of the transformer I mama frequency which is determined by transformer are constant.

1 may be computed and so predetermined from 'mum value. Transformer T2 is given the the inductance of the transformer and the capacities attached to it. The simplest case is where the capacities attached to the This 'is the case where the transformer works intoa detector tube as shown in Fig. 1 of the drawings. These, capacities may be measured at any frequency and the natural of the" transformer the 'coil' inductances and 'the capacities.

The results. accomplished by constructing a cascade amplifier system suchas hereinmeasured -'before described is shown inFig. 3 of the drawing's'niherein is depicted the difference between an nntune'd stage constructed in accordance with the prior art and an automaticallyituned stage constructed in ac cbrdance with the-principles of the'present inventionQ-The dotted line curve inFig.-

3 shows theamplific'ation obtained with an untunedst e of the prior art and-the-full line curve ows how theamplification-of a system of my present invention'instead of decreasing from a. eak or maximum is maintained substantia -y constant over the wave length range. Infproducing the de-'" sired resultin amplification curve the precaution should be observed of building the transformer T with a natural wave length within a given range. It is found'that when this transformer is constructed to have the shorter natural yvave lengths, the resulting am'lification becomes peaky. For example,

awive length shorter than 450 meters for-the transformer T creates a peaky condition whichsoon runs into an unstable or oscilla tory condition. This henomena I designate as overtuning and s ould be avoided in the design of the transformer. When the transformer T2 has too short? a natural wave length, the tube input capacity of the tube V1 risesso fast with frequencyas to cause transformer T1 to'have a natural freuency of oscillation lower than the natural,

'equency of T2. In this condition the tube T2 exerts a very strong regenerative feed-' back effect -on the tubeTl and creates a sharply peaked regenerative gain in am-- plification withits undesirable instability.

in the amplifier and the production ofcurrents of local oscillations.

The use and operation of the amplifier system embodying the principles offm present ,invention and the numerous vantages thereofwill-in the main be fully apparent from the above detailed description thereof;] It will be further ap arent that while 'I- have shown and descri ed my in- Ventionin the preferred form, many changes and modifications may be made in the structure disclosed without"departifig from the spirit o ing claims.

I clain'r: 'i I 1. An electron discharge. tube amplifier system comprisin an electron discharge tube havingfinput an output electrodes, an inductive input circuit connected to the-input, electrodes, the said input circuit having fixed. constants including a given tube input cal-j pacity,-, and an impedance output circuit network connected to the output electrodes, the said impedance output -'c1rcuit network having constants effective with the change in frequency over a given wave length band for varying the said tube inputcapacity' over said wave length band so as 'to maintain the 00 f inductive input circuit resonant over said given wave length band. r

2. electrondischarge tube amplifieii system comprising anjelectron discharge tube having input and output electrodes, an input circuit connected to t 6 input electrodes and including a transformer, the said input circuit having fixed constants includinga given tube input capacity, and an output circuit network connected to the 'output'electrodes 1 0 and including a second transformer, the said second transformer in connected circuit having constants effective with .the change in frequency over a given wave length band for varying the said tube input capacity over said wave length band so as to maintain the said input circuit resonant over said givenwave length band.

3. An electron discharge tube amplifier system comprising an electron discharge 1' tube having input and output electrodes, an input circuit connected to the input elect-- trodes and'including a bifilarly 'wound trans- 'former,'the said input circuit having 'fixed lff. constants including a given tube input} 1&5 capacity, and an output circuit network con nected to the output electrodes including a" second bifilarly wound transformer, the said" second transformer having constants effective with theichan ge in-frequency over a given Wave length band for varying the said tube input'calp'acityover said wave length band so as to maintain the inductive input circuit resonant over said given wave length band.

.' 4. An electroii discharge; tubeiamplifier fzs system comprising-an electron discharge tube, having input anfd output electrodes, an input circuit connected to'the input electrodes and including a bifilarly wonndtransformer, the said input circuit having fixed constants inno f the invention,"dei ined in the follow- 76 I cluding a given tube input capacity, and an output circuit network connected to the output electrodes including a second bifilarly' havinggrid, plate and filament electrodes, an inductive Input circuit connected to the grid and filament electrodes, the said input circuit having fixed constants and the said tube having capacity between the grid and plate electrodes, and an impedance output circuit network connected to the plate and filament electrodes, the said impedance output circuit network having constants efiective with the change in frequency over a given wave length band for varying the said grid-plate capacity over said wave length band so as to maintain the inductive input circuit resonant over said given wave length band.

6. An electron discharge tube amplifier system comprising an electron discharge tube having grid, plate and filament electrodes, an input circuit connected to the grid and filament electrodes including a transformer,

';the said input circuit having fixed constants and the said tube having capacity between the grid and plate electrodes, and an output circuit network connected to the plate and filament electrodes and including a second transformer, the said second transformer having constants effective with the change in frequency over a given wave length band for varying the'said grid-plate capacity over said wave length band so as to maintain the inductive input circuit resonant over said.

given wave length band.

- 7. An electron discharge tube amplifier system comprising an electron discharge tube havin grid, plate and filament electrodes, an inductive input circuit connected to the grid and filament electrodes, the said input circuit having fixed constants and the said tube having capacity between-the grid and plate electrodes, and an impedance output circuit network connected to the plate and filament electrodes, the said impedance output circuit network including a bifilarly wound transformer'having constants effec tive with the change in frequency overa given wave length band for varying the said grid-plate capacity over said wave length band so as to maintain the inductive input circuit resonant over said given wave length band; v

8. An electron discharge tube amplifier system'havinga high amplification over a relatively wide wave length band comprising an electron discharge tube having input and output electrodes, an inductive input circuit connected to the input electrodes, the said input circuit having fixed constants including a given tube input capacity, and an impedance output circuit network connected to the outputelectrodes, the saidimpedance output circuiitQnetwork having a natural. frequency corresponding to the lowest frequency of said wave length band so as to be efiective with the'change in frequency over said wave length band for varying the said tube input capacity to main" tain the inductive inp'ut'circuit resonant over said given wave length band.

'9. An electron discharge tube amplifier system having a'high amplification over a relatively-wide wave length band -comprising an electron discharge tube having input and output electrodes, an inductive input circuit connected to the input electrodes, the said input circuit having fixed constants ineluding a natural frequency corresponding to the highest frequency of said wave length band and. also including a given tube input capacity, and an impedance output circuit network connected to the output electrodes, the said impedance output cir c uit network having a natural frequencycorresponding to the lowest frequency of said wave length band so as to be elfectivewiththe change in frequency over said wave length band for varying the said tube input capacity to main-Y .tain the inductive inputfcircuit resonant over said given wave length band.

10. An electron discharge tube amplifier system havin a high-amplification over a relativel wi e wave length band comprising an e ectron discharge tube having input and output electrodes, an input circuit connected to the input electrodes and including a transformer, the said input circuit having fixed constants including a given tube input capacity, and an outputcircuit network con- 'nected to the output electrodes and including a second transformer, the said second transformer havinga natural frequency corresponding to the lowest frequency of said wave length band and having low distributed capacity in and low magnetic leakage be tween the coils thereof so as to be effective with the change in frequency'over said wave length band for varying the said tube input capacity to maintain the inductive input circuit resonant over said given wave length band.

11. An electron discharge tube amplifier system comprising an electron discharge. tube having input and output electrodes, an inelectrodes, the said input circuit having fixed constants including a given tube input capacity, the said constants being such that a predetermined variation in said tube input capacity over a given wave length band maintains the said input circuit resonant over said given wave length band, and an impedance output circuit network connected to the output electrodes, the said impedance output circuit network having constants effective with the change in frequency over said wave length band for producing the said predetermined variation in said tube input capacity.

12. An electron discharge tube amplifier system comprising an electron discharge tube having grid, plate and filament electrodes, an input circuit connected to the grid and filament electrodes and including a transformer, the said input circuit having fixed constants and the said tube having ca.- pacity between the grid and plate electrodes, the said constants being such that a predetermined variation in said grid-plate capacity over a given wave length band'maintains the said input circuit resonant over said given wave length band, and an impedance output circuit network connected to the plate and filament electrodes and including a second transformer, the said impedance output circuit network having constants effective with the change in frequency over said wave length band for producing the said predetermined variation in said grid-plate capacit 13. An electron discharge tube amplifier 1 system comprising an electron discharge tube circuit having fixed constants including a given tube input capacity, the said constants being such that a predetermined variation in said tube input capacity over a given wave length band maintains the said transformer input circuit resonant over said 'given' wave length band, and anoutput cirsaid second. transformer having constants effective with the change in'frequency over said wave length band for producing the said predetermined variation in said tube input capacity.

14. An electron discharge tube amplifier system having a high amplification over a relatively wide wave length band 'comprising an electron discharge tube having input and output electrodes, an input circuit connected to the input electrodes and including a transformer having a natural frequency corresponding to the highest frequency of said band, the said input circult having fixed constants including a given tube input capacity, the said constants being such that a predetermined variation in said tube input capacity over a given wave length'band maintains. the said input circuit resonant over said; given wave length band, and an impedance output circuit network 'connected to the output electrodes and including a sechaving a natural frequency corresponding to the lowest frequency of said wave length band so as to be effective with the change in frequency over said wave length band for producing the said predetermined variation in said tube input capacity.

Signed at New York, in the county of New York and State of New York, this 8th;

day of June A. D., 1927. I I

' LESTER L'. JONES;

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