US1517057A - Vacuum-tube amplifier - Google Patents

Description

Nov. 5, 1924;

7 5 R o l. T m m $3 mm s W mm m w w w Y E W N r .(FQ G w m Wh m. WM, A um .M U d I lnlv D w m BM ww M a To all whom it may concern.

Patented Not. 25,1924.

DAVID emmns, or GRASMERE, new YORK.

VACUUM-TUBE AMPLIFIER.-

Application filed September 19, 1922. Serial No. 589,108.

Be it known that LDAVID GniMns, a citi zen of the United States, and a resident of Grasmerc, county of Richmond, and State of New York, have invented certain new and useful Improvements in Vacuum-Tube Amplifiers, of which the following is a specification.

This invention has to do with high frequency signaling systelns,and relates, more particularly, to radio and other high frequency receiving, amplifying and repeating systems and circuits therefor.

In so-call'ed vacuum tube reflex circuits, particularly high frequency receivingcircuits as described in United States Patent No. 1,087,892, issued February 17, 1914, to Schloemilchand Von Bronk, and British Patent No. 132,668, issued to Marius Latour, as well as numerous other patents and publications, the same thermionic-vacuum tubes are utilized to effect both radio frequency, and audio frequency amplification simultaneously. In the reflex systems comprising a plurality of amplifying tubes heretofore known, the radio frequency amplification and audio frequency amplification. were effected by the tubes in corresponding order of sequence. For example, let. it be assumed that a reflex receiving circuit of the heretofore known type comprises three vacuum tube amplifiers and a detector. The incoming radio. frequency signaling currents are impressed on the amplifier tubes successively in the order 1, 2 3 and amplified by each tube, after which the amplified high frequency signaling current is impressed on the detector, from which audible frequency current variations corresponding with the signals are derived. The audible frequency currents are then impressed on the same amplifier tubes as before and likewise in the order 1, 2, 3. The amplified audio frequency currents are then impressed. on a suitable indicating device such as a loud speaking telephone.

From a consideration of the foregoing it will be seen that the first amplifier tube has impressed upon it both. the weakest radio .frequency currents and the weakest audio frequency currents, while the third amplifiertube has impressed on it highly amplified radio frequency currents and highly amplified audio frequency currents. It follows that with such an arrangement the amplifier tubes are most unevenly loaded and that one tube may be very lightly loaded while another is overloaded. To overcome the aforementioned disadvantage inherent in previous reflex circuits and therefore to increase the efficiency of operation of amplifier tubes, is one of the principal objects of the present invention.

A further disadvantage greatly in evi:

Hence in previously known reflex circuits employing more than one stage of radio frequency amplification arises from the strong "tendency to oscillate at high frequencies.

This tendency comes about from the fact that even the most feeble radio frequency oscillations whichmay be transmitted from the output side of the detector to the input side of the first amplifier tube through the medium of the intervenin audio frequency transformer or other audio frequency path are generally so greatly reamplified by the succeeding tubes as to be sustained. This condition is of course likely to result in highly undesirable beat notes and does in fact so result. The elimination of the lastmentioned undesirable conditi'on is a furtherobject of'the present invention.

As in the known reflex circuits referred to, the present invention contemplates using the same vacuum tube amplifiers for effecting both radio frequency amplification and audio frequency amplification, but instead of passing the audio frequency currents through the amplifier tubes in the same sequence as the radio frequency currents, thus unevenly loading the tubes, the sequences are reversed, that is to say, the audio frequency amplification is effected by the amplifier tubes in the inverse order or sequence as compared with the order or sequence in which the amplifier tubes are utilized for effecting radio frequency amplification. By comparison with the explanation previously given, it will be seen that a more even loading of the tubes is effected.

This results ,in materially increased efti ciency and improved quality of tone repro duction arising from the reduction or elimination of tube distortion.

The elimination or reduction of the tendency to sustain high frequency oscillations is accomplished in the circuits of the present invention by reason of the fact that the out put of the detector is impressed on the input circuit'of the last amplifier tube instead of one of the preceding tubes as heretofore,

and accordingly any high frequency oscilla-v tions which ma be tmimiaea from the .output of the detector totheiinput'of thelast amplifier tube through themed umof \the intervening audio frequencyfpath is ama plified by only one tube, been should be borne in mind that theienergyof the oscillations under consideration" is exceedingly small when impressed onthe input of the amplifier tube due to the attenuationof the audio'frequency path, and that after a single stage of. amplification it is still very small. -'When these weak oscillations are further attenuated by the. succeeding audio frequency path through which they must pass, if they pass at all, their energy is fur ther reduced to such an-extent that they areincapable of being built up by the succeeding amplifier tubes to a sufiicient extent to 7 result in their being sustained. The foreoing theoretical consideration appears-to e consistently borne out-by the results which havebeen'obtained in practice. It it thought desirable to point out, however, that the same factors have to be taken into consideration for the prevention of free osexceed the negative resistance.

cillations as "in any vacuum tube-circuit arrangement wherein energy-may be fedback from the output to the input circuit, namely, that the positive resistance must words, the attenuation of the frequency oscillatory energy must outweigh the effective amplification. If, then, vacuum tube amplifiers having high" amplification fac-' tors are employed, the high frequency im pedances of the audio frequency paths (this refers more particularly to the mutual capacities' between the windings of the audio frequency transformers-which capacities 40 .must be correspondingly low for high impedance to radio frequencies) must be correspondingly high, but if the amplification factor is low, the high frequency imped ances may be correspondingly low. Since the vacuum tube amplifiers to be employed are usually decided upon in, advance, the controllable factor in the design resides in 1 the audio frequency path. The desired high frequency impedance, or, more specifically, low mutual capacity between windings, maybe and generally is obtainable by proper design of the audio frequency transformers without any ancillary apparatus for increasing the high frequency-impedance being provi ed.

' For the purpose of distinguishing circuit arrangements according'to the present invention, the term .inverse duplex has been coined and adopted. As may easily be im plied, this term refers to circuits wherein some or all of the amplifier tubes are util-. i'zed for both radio frequency and audio frequency amplication (thus dup'lex) and that the tubes are efi'ective .in the inverse order as already explained. The term in- In other quencies, but very high.

verse duplex therefore has a definite mean it is desired be scrupulously obing which served. i

In the following. detailed'de'scription of one of the preferred embodiments of the jects will be pointed out. I, I

The drawingshows a circuit diagram of an inverse duplex receiver-and amplifier comprising three amplifier tubes 1, 2 and 3 and detector. tube 4; Each of the tubes is invention additional novel features and obof the three electrode. type. including filacept that there-must be at least two stages of radio frequency amplification and twostages of audio frequency amplification. In some cases it may bedesirable to have only twostages'of audio frequency amplification and three stages of radio 3 frequency, in

which event. any two of the amplifier tubes may be utilized for audio frequency am plification; A number of other arrangements, may also bev resorted to'depending upon the total number of amplifier tubes and the amount of radio frequency and audio frequency amplification desired.

Conductors 17,-18 may'extend to a radio receiving system such asantenna and-ground respectively or to theterminals of a loop or they may connect with a metallic trans mission l ne as in the case of so-called carrier current or wired radio telephone systems.

Variable condenser 16 is provided for tuning purposes, and is used, more particularly, when the apparatus is provided with I a loop antenna, which for the present purposes it will be assumed is employed.

The incoming ,high frequency signaling.

currents supplied by the loop are conducted through the medium of condenser ligand 1 conductor 57 to the grid 38 and filame iiti; 6. Condenser, 29 is designed topass the blocking audio frequency -current. weak high frequency current being amplified in the usual way in tube 1 appears in amplified form in the high frequency outlet put circuit of tube 1, which includes plate 39, primary windiiw 50 of radio frequency transformer 5, condenser 28 and filament 46. Condenser 28 is generall of low capacity, providing a by-pass or high freimpedancc for low h gh; frequency currents while substantiallfyiflzo The minor? frequencies. The adjacent-input and out-' putsides of succeeding tubes are intercon nected through the medium of high frequency transformers 5, 6 and 7, each of which is designed to pass high frequency currents but to provide no path, or at most a very inefiicient path for audio frequenc currents. and 2 which are provided asby-pasSes for the high frequency currents are of such proportions as to greatly impede the passage of audio frequency currents. The high frequency currents are repeatedly amplified by the amplifier tubes in the order 1, 2, 3 and finally pass through the medium of transformer 7 to detector tube 4. The input circuit of the detector tube includes a grid condenser and leak 37, the function of which is well known."

The detector tube converts the super-aud-ible high frequency energy into audible frequency currents in the usual manner.

The output circuit .of the detector tube includes'plate 45, filament -49, battery 13 and primary winding 35 of the audio frequency transformer 10. As previously stated, condenser 23 functions to bypass any high frequency currents which may appear in the output of the detector, thus greatly reducing the energy of any high frequency cur rent output which might be conducted to the primary winding 35 oftransformer 10.

Amplifier tube 3, being the last in theseriesv of radio frequency amplification steps, and therefore most heavily loaded at radio frequency, is utilized for the firstaudio frequency amplification step. Secondary winding 34 of transformer 10 is accordingly connected tothe input'circuit of tube 3 in series with the secondary winding of radio frequency transformer 6, conductor 59 and grid 42. The other endof secondary winding 34 is connected to filament 48 through. contact 36 of potentiometer 15. The audio frequency current is therefore impressed across the grid 42 and filament 48'and is amplified by-tube 3. I The output circuit of amplifier tube. 3 in udes plate 43, primary winding 54 of the radio frequency transformer 7, primary winding 3 of the audio frequency transfo'rmeryf), batteries 13. 14 and filament 48 all in series.

Secondary winding 32 of transformer iii-is connected with the input circuit-of the am plifier tube in the same manner as the sec' ondary winding 34 of transformer 10 con-. nected with the input circuit of amplifiertube 3.

The audio frequency input circuit ofamplifier tube 2 includes grid 40, conductor 58, secondary winding 51 of radio frequency transformer 55, secondary winding'32 of Condensers 23, 24, 25, 26

uen'cy current from the output I of amplier tube 2 to the input of amplifier tube 1 is efl'ected, as in the preceding instances,

through the medium of audio frequency transformer 8 which includes a primary winding 31 connected in the output/circuit of amplifier tube 2 and secondary winding30 connected in the in ut circuit of amplifier tube 1. The seconc ary winding 30 is preferably, but not necessarily, connected, as shown, to one side of the filament 46 through conductor 61." A direct connection between secondary "winding 30 and grid 38 of amplifier tube 1 may be effected through the loop which would ordinarily be connected to the terminals of conductors 17, and'18. In the event of the apparatus being used in conjunction with an ordinary antenna ora metallic transmission line, the secondary coil of a variocoupler may be connected across the terminals with the conductors 17- and 18, thus providing a Cit path for the audio frequency currents in the input circuit of amplifier tube 1.

The audio frequency output circuit of amplifier tube 1 includes the plate 39, primary winding 50 of radio frequency transformer 5, a suitable indicating device 11 such as a loud speaking telephone, batteries 13 and 14 and filament 46.

so i

The iron cores of transformers 8, 9 and 10 are preferably grounded to the output filaments as indicated, for instance, by con ductor 62. I

Filament resistances 19, 20 and 21- may be fined as indicated, and their value is deter mined by the filament current requirements and the voltage of the filament lighting battery 12. Resistance 22 is preferably variable on account of being associated with the detector tube 4, which is more critical on filament temperature than are the amplifier tubes. 3

Since amplifier tube 1 effects the least radio frequency amplification and, contra, the largest audio frequency amplification, and since the reverse is true of amplifier tube 3, it is evident that the load on these two tubes tends to approach equality. The

sa -me'is apparently true with respect to amfplifientube 2, since the radio frequency and audig frequency loads, respectively. are in.- terinediate those carried by tubes 1. and 3.

By ireason'of this novel arrangement, it. is

found that the amplifier tubes may be operated with increased efficiency and that the quality of the output is'materially' improved. It has been explained in a preceding paragraph how the circuit arrangement under consideration is effective to suppress the formation of high frequency sustained oscillations, but a further explanation in' connection with the circuit diagram is thought to be not out of order. Any high frequency feedback from the output of detector tube 4 which may reach the input of amplifier tube 3 must pass through transv former 10'.

Any high frequency leakage of this character is amplified by tube 3 and returned, in part, to the input of detector tube 4 through transformer 7, and, in part, to transformer 9', from'which it may be conveyed to the input of tube 2, and, in turn, through transformer 8 to the input of tube 10 1. Sineethe attenuationat high frequencies of transformers 8,9 and 10 is very high, the high frequency currents which maybe, fed back therethrough are accordinglyv very weak. If the attenuation. of

It, transformer 10 due to the low mutual ca- Ell pacity between the windings more than of sets the effective amplification of tubes 3 and 4, the high frequency oscillations under consideration cannot, besustained by tubes 3 and 4: alone. Butit is-neeessaryto take into consideration-the possibility of some of the highfrequency current leakage finding its way back asfar' as the input of tube 1, .and that, such being the case, all the tubes are available for re-amplification. Ina circuit comprising several tubes, the amplification and attenuation of high frequency leakage presents quitea complex situation which is not easily calculated with accuracy, but the fact remains that if-the efiective attenuation of the audio frequency paths to the high frequency oscillations is suflicient to more than offset all the effective amplification available to such high frequency leakage as may exist, there can-be no sustained oscillations set up. It is, therefore, essential to the best practice that the transformers 8, '9 and 10 be designed to provide sn'flicient attenuation at hi glrfrequencies e., that 40 the mutual capacity between windings be sufficiently low) or that some provision be made externally of the audio frequency transformer for obtaining the necessary attenuation.

A further comparative advantage in the present system over the heretofore known reflex circuits arises from the fact that the telephone 11 is connected to the output of the amplifier tube immediately adjacent the loop. This provides only one stage of amplification for any audio frequency disturbing currents which may reach the loop, such, for example, as the cycle current ofneighboring electric light lines. It has been found that a single stage of a1nplificarion is usually insufiicient to increase the intensity of low frequency disturbances to a point where they become materially noticeable, whereas with-two or three stages of amplification, such disturbances may be of such strength as to practically obliteratethe signals. Although the explanation herein contained concerning the theory of operation of the system described are believed to be correct, the invention is in no way dependent upon an accurate understanding of the theory and should not be construed as limited by such considerations. Neither is 'it essential to the invention that the elements of the circuit be designed to prevent sustained oscillations, although-that is generally the preferred'practice.

' Having thus described my invention, what I claim and desire to secure by Letters Tatentis 1. A system comprising a. plurality of amplifiers arranged for interstage operation, I

.and circuit connections for said amplifiers,

said circuit connections bein so arran ed that sa1d amplifiers are operable to ampl fy current variations of two different bands offrequencies, and means including said circuit connections whereby the current variations. within one band of frequencies are impressed upon the amplifiers in a predetermined order, and the current variations within the other band of frequencies are impressed upon the amplifiers in the inverse order as compared with the aforementioned predetermined. order. I

2. A multi-sthge amplification system comprising a plurality of amplifiers, circuit connections for said amplifiers, the arrange- 'ment being such that superaudible high frequency current variations are repeatedly amplified by said amplifiers in a predetera plurality of-said amplifiers are rendered operable to repeatedly amplifythe audible frequency current variations from said rectifying means in the inverse order as compared with the aforen'icntimwd predetermined order.

4. A multi-slagc amplilimu ion system comprising a plurality of thermionic amplifiers arranged to repeatedly amplify modulated super-audible high frequency current variations in a. predetermined order, means interconnecting said amplifiers operable to transmit super-audible high frequencycurrents with relatively high effi- MCIQHCY but inoperable to transmit audible frequency currents to an appreciable extent, means for rectifying the amplified superaudible high frequency'output of said amplification system. whereby audible frequency current variations are derived, and means whereby a plurality of said amplifiers are rendered operable to repeatedly amplify the audible frequency current variations from said rectifying means in the inverse order as compared with the aforementioned predetermined order, said last-mentioned means being operable to transmit audible frequency current variations with relatively high efficiency, but inoperable to transmit super-audible high frequency current variations-to an appreciable extent.

5. A multi-stage amplification system comprising a plurality .of thermionic amplifiers and circuitconnections for said amplifiers, said. circuit connections being so arranged that said amplifiers are operable to repeatedly amplify current variations of two different bands of frequencies, and means including said circuit connections whereby the current variations withinone band of frequencies are impressed upon the amplifiers in a predetermined order, and the cu'rrent'variations within the other band of frequencies are impressed upon the amplifiers in the inverse order as compared with the aforementioned predetermined order.

6. A multi-stage amplification system comprising a plurality of thermionic amplifiers having input and output circuits and arranged to repeatedly amplifysuper-audible high frequency current variations in apredetermined order, one or more transformers operable to pass super-audible high frequency currents with-relatively high efficiency but inoperable to pass audible frequency currents to an appreciable extent, succeeding ones of said amplifiers being inter-connected in each instance through the medium of one of said transformers,- means for rectifying the amplified super-audible high frequency currents and thereby obtain-.

ing audible requency current. variations, means operable to'transmit the audible frequency currents from said rectifying means to the input circuit of one of said amplifiers wherein the audible frequency current variations are amplified, and means operable to transmitv the amplified audible frequency current from the output circuit of said lastmentioned amplifier-to the input circuit of another of said amplifiers wherein further audible frequency amplification is effected, said two last-mentioned amplifiers being operable to amplify audible frequency current variations in-the inverse order as compared with the order in which they are operable to amplify super-audible high frequency current variations.

7. In a signaling system, two thermionic amplifiers in cascade relation, input and output circuits for said amplifiers, a radio frequency transformer having its primary winding connected in the output circuit of the first of said amplifiers and its secondary winding in the input circuit of the second of said amplifiers, a second radio frequency transformer having its'primary winding in the output circuit of said second amplifier, a rectifier, the secondary winding of said second transformer being connected in circuit with the saidrectifier, an audio fre-- quncy transformer having its primary winding connected with said rectifier, the secondary winding. of said audio frequency transformer being connected in the input circuit of said second amplifier whereby low frequency current variations derived from said rectifier are impressed upon the input circuit of said second amplifier wherein they are amplified, a second audio frequency transformerhaving its primary winding connected in the'output circuit of said second amplifier and its secondary windin in the input circuit of said first amplifier whereby the audible frequency current variations are further amplified by said first amplifier.

8. A system comprising a plurality of vacuum tube amplifiers each including a cathode, an anode and a control electrode,

circuit connections for said amplifiers, said said last mentioned amplifiers amplify cur- I rent variations within said first mentioned band of frequencies.

4 9. A multi stage" amplification system comprising a plurality of amplifiers, circuit connections for said amplifiers the arrangement being such that super-audible high he quency current variations arev repeatedly amplified by said amplifiers in a predetermined order, and means whereby a plurality of said amplifiers are rendered operable to repeatedly amplify audible frequency currentvariations in the inverse order as compared with the aforementioned predetermined order, both the super-audible and audible frequency current variations beingamplified simultaneously. I

10. A malti-stage amplification system comprising a plurality of three-electrode vacuum tube amplifiers arranged to repeat.

edly amplify modulated super-audible high frequency current variations in a predetermlned order, means, interconnecting said amplifiers, operable at relatively high efficiency to transmit su er-audible" high frequency currents but at ow'efliciency to transmit audible frequency currents, a three-electrode vacuum tube detector having its input electrodes connected to the output end of said amplification system, and means whereby a plurality ofsaid amplifiers are rendered operable 'to repeatedly amplify the audible frequency current variations from saiddetector I in the inverse order as compared with the aforementioned predetermined order, said last-mentioned means being operable at relatively high efficiency to transmit super-audible high frequency currents.

' ther amplification in each successive step.

5 12. The method of signal reception and amplificatidn which consists impressing modulated .high frequency sigaling -current on a plurality of amplifiefs m seriatign and effecting further amplification in eaclrs'ucq cessive step, convert ng the amplified hi b frequency signaling current into audib e1 frequency signaling current, impressingtlfe' audible frequency signaling current on the y same amplifiers in' seriatim but 'in the :iii'iverse orden and effecting further amplifica -tion of, the audiblefrequen'cy currents in;

each successive step.

13. The method of utilizing vacuum tubes as amplifiers,-whi'ch consists in utilizing the "1 tubes in a predetermined sequence for repeatedly amplifying high frequency varia-[ tions, rectifying the amplified high. frea quency variations thereby obtaining-lower frequency variations, andsubsequently uti lizing tne same tubes in inverse sequence for repeatedly amplifying the ,lower frequency variations,

Inwitness whereof, Ihave hereunto set my hand this 18 day of September, 1922.

DAVID GRIMES/

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