US2416334A - Thermionic valve amplifier - Google Patents

Thermionic valve amplifier Download PDF

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Publication number
US2416334A
US2416334A US435983A US43598342A US2416334A US 2416334 A US2416334 A US 2416334A US 435983 A US435983 A US 435983A US 43598342 A US43598342 A US 43598342A US 2416334 A US2416334 A US 2416334A
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Prior art keywords
potential
plate
capacity
grid
suppressor grid
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Expired - Lifetime
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US435983A
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English (en)
Inventor
Levy Maurice Moise
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International Standard Electric Corp
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International Standard Electric Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/08—Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/50—Amplifiers in which input is applied to, or output is derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
    • H03F3/52—Amplifiers in which input is applied to, or output is derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower with tubes only

Definitions

  • This invention relates to improvements in amplifier circuits using pentode Valves. vit concerns the reduction of the effect of certain stray capacities associated with such valves.
  • the principal object of the invention therefore is to improve the operation of pentode amplifiers at high frequencies by the elimination, partly or wholly, of the effect of the'stray capacities associated with the platecircuit of the pentode valves.
  • This object is accomplished by connecting the suppressor grid of any such pentode to some point in ,the amplifier, the alternating potential of which is equal to or nearly canal to the alternating potential of the plateof the pentode.
  • the terminals of the capacity between the plate and the suppressor grid'ivvh ch frequently is a large fraction of the total plate capacity) are maintained at nearly the same potential.
  • the current which would flow through this condenser is reducedto a verysmall value.
  • the suppressor grid is made to screen the plate from earth, and the princi le may be extended by supplying the external connections to the plate of the ,pentode with a screen which is connected to the suppressor grid, and in this way the capacities'associated with the external circuit are also eliminated or reduced.
  • the efiect of this process may be regarded as equivalent to connecting across the unwanted capacity a negative capacity by which it is neutralised.
  • the point in the amplifier to which thesuppressor grid should be connected should betweenthe point and earth :is relatively low in order that the-capacity which will the introduced by the connection of the suppressor grid and the external screen, if any,may have aninappreciable effect.
  • the phase of the alternating potential of the point to which the .suppressor grid is connected shouldpreferably be .the same as the phase of the alternating potential whichappears on the plate of the .pentode in .order that the corresponding difference-ofpotential'shall at all-times be small. It mayhappen that .the'point to which it is vdesired to connect .thesuppressor grid has the op posite phase in which case connectionis made through a transformer, the windings of which are connected in such a direction that the desired phase isproduced on the suppressor grid. 7
  • the alternating potential of the suppressor grid may also be chosen to be higher than that .of the .plate of the pentodein which case additional current is fed through the stray capacity concerned. This enables other straycapacities associated with the plate impedance to be neutralised.
  • the phase of the alternating potential applied to the suppressor grid may be chosen to have :any relation .withrespect to the phase of the plate and by this the-effect of shunting the capacity between theplateand suppressor grid by any impedance, positive .or negative, can be produced.
  • an amplifier consists of-afirst pentode-stage followed by other stages comprising valves connected as cathode followers.
  • the suppressor grid of the pentode is connected to the cathode of the following valve, the AC potential of which will generally-be very nearly the same as the 'potential of the plate of the pentode.
  • the impedance to ground of this cathode is usually small compared "with the 'impedance to ground of the plate-of the pentode.
  • the principles of the invention which have just been explained are carried out. The same arrangement may be adopted for *any pentode in any of the subsequent stages of the amplifier.
  • the amplifier come prises some stages with negative cathode feedback.
  • the cathode of any valve is then connected :to the suppressor grid of the preceding valve. "In this way, the capacity between the plate andrsuppressorgrid oicertain of the valves may be reduced by *an amount depending upon the value of the negative feedback of the corresponding ,following valve.
  • Fig. 4 shows an embodiment in which a pentode valve is followed by a valve connected as a oathode follower
  • Fig. 4A shows a modification of the embodi-- ment shown in Fig, 4.
  • Fig. shows the circuit of an amplifier hav-.
  • a pentode valve V! which may form part of an amplifying circuit.
  • the load impedance Z of the plate circuit is shunted by a series of stray capacities which limit the amplification of the circuit at high frequencies. These capacities can be conveniently divided into two portions; CI which represents the capacity between the plate and the suppressor grid, and
  • C2 which represents the capacity to .ground of the plate (exclusive of CI and of the connecting leads.
  • Fig. 1 is intended to show the circuit effective as regards the amplification of high frequency voltages, which may be assumed to be. applied to the control grid. The arrangements for polarising the plate and grids and other details are accordingly omitted.
  • the effect .ofthe capacity CI can be reduced if a varying potential, in phase with the plate potential producedgby thesignalapplied to the grid, be connected to the suppressor grid. If" this varying potential be nearly equal to the plate potential, then the voltage across the condenser CI will always be small and its effect will thus be greatly reduced.
  • FIG. 1 which shows the essential circuit characteristics of Fig. 1.
  • the points A and S correspond in the two circuits,
  • the plate circuit is represented by a generator GPin series with, an impedance ZP corresponding to the internal output impedance of the valve.
  • the effect of the generator can be regarded as equivalent to connecting a negative capacity parallel with Cl, whose value depends upon the voltage of the generator. It is also possible to produce the effect of connecting various kinds of 1 I negative or positive impedances in parallel with CI by'suitably choosing the amplitude and phase I of the output of the generator GS with respect to GP.
  • ThegeneratorGS in series with ZS represents the effect of connecting thevary- 4 a point of constant potential (normally equal to ornear that of the cathode) in order to maintain it at a potential sufiiciently low with respect to the plate to suppress the secondary electrons produced thereat.
  • the potential difference between the plate and the suppressor grid will thus usually be equal to or a little less than the applied plate voltage.
  • Thealternating plate potential in an i amplifying valve due to the signal is however generally small compared with the applied plate Voltage, and accordingly the suppressor grid can be connected to a point of alternating potential without substantially affecting its function in suppressing the secondary electrons, so long as this alternating potential is of the same order as the alternating plate potential. In general this will be the case and in the most interesting case when the potentials of the plate and suppressor grid Vary in phase for eliminating the elfect of 0!, the difference of potential between the plate and the suppressor grid will be maintained approximately constant.
  • Fig. 3 shows schematically one way in which the desired varying potential may be obtained.
  • the block A represents the remainder of the amplifier of which the valve V! is supposed to form a part.
  • the effective ground capacity of the suppressor grid is represented by C3.
  • the required variable potential for the suppressor grid is preferably taken from some'point 7 'PI in the amplifying circuit as shown where the impedance to ground is sufficiently small for the eifect of the capacity C3 added in parallel to be unimportant.
  • a particularly interesting case is that in which the amplifier works into a low output impedance Z0. If the output potential is in phase with the plate voltage of the valve VI 7 the suppressor grid may be connected to the out- According to the usual method of. operating put at P2, for example. If there is phase opposition, a transformer T may be connectedin front of Z0 as indicated in Fig. 3A, and the suppressor grid can be connected to the output side of the transformer at P2.
  • the capacity G3 which now comes in parallel with Z0 will have a negligible eifect because Z0 is small.
  • a transformer may also be used in a manner similar to that just described.
  • Fig. 4 shows the circuit of a two-stage amplifier which exhibits certain other aspects of the invention.' The stray capacities CI, C2 and C3 are shown in dotted lines associated with the first valve VI; The second valve V2 is shown connected as a cathode follower.
  • the suppressor grid of the valve V! is connected to the cathode of V2, and on account of the fact that V2 is arranged as a cathode follower, the potential of the suppressor grid of VI will be generally nearly the same as the potential of the grid of V2. As this grid is coupled to the plate of VI through the condenser KI follows that the potential of the suppressor grid of VI will always be very nearly the same as the potential of the plate. Thus the effect of the capacity CI will be practically eliminated.
  • V2 is connected as a cathode foilower, the cathode resistance RC2 can be very small will accordingly be negligible because RCZissmall.
  • valve Vi is a high slope pentode
  • the capacity between the plate earth will be about 9 a y.
  • the capacity to earth of the grid of valve V2 might be about 12 12, but since this valve is connected as a cathode follower the eifect of this capacity could be re depicted to for instance, because the grid and the cathode will be nearly at the same potential.
  • the grid earth capacity of V2 can be taken as effectivelyv equal to about 1.2
  • the capacity to earth of theexternal connections to the plate of VI can generally be arranged to be not more than about 2 u.
  • the total effective capacity to earth of the plate of VI would be that is, if the suppressor grid of VI is not connected to the grid of V2, When, however, this connection is made, the effect of the capacity CI may be reduced to In many valves, Ci will be 80% of the total plate-earth capacity that is, about 7 say. Accordingly the capacity CI is effectively reduced to about 0.7 m.
  • the total capacity of the plate of VI now becomes that is, a little less than of the preceding value. With a given value, and with the same circuit configuration, therefore, it would now be possible to increase the plate resistance Z! twice, thereby increasing the gain by 6 decibels.
  • the suppressor grid forms a partial screen between the plate and earth.
  • This screen may be extended as shown in Fig. LA to include the external connections to the plate by surrounding them by a conducting metal screen M which is connected to the suppressor grid.
  • This screen could with advantage include also the condenser KI which couples the plate of VI to the grid of V2 in Fig. 4. This will have the eifect of suppressing part of the capacity C2 because most of it now comes in parallel with CI.
  • the capacity of the screen which has been added will, of course, increase the capacity C3, but so long as this increase of capacity is not too great, or so long as the resistance RC2 is sufficiently small, this will not introduce any objection.
  • Fig. 5 is shown a three-stage amplifier containing valves connected with negative reaction and in which the capacity of CI is effectively suppressed in a manner very similar to that of Fig. 4.
  • the first valve VI is connected as an ordinary amplifier without reaction and has a shunted biassing resistance GI connected in series with the cathode. It is coupled to the next valve V2 by means of the plate resistance ZI and the coupling condenser KI.
  • Valve V2 is provided with a shunted biassing resistance G2 and also with a resistance RC2 in series to provide the negative reaction.
  • This valve is in turn coupled to the valve V3 by means of plate resistance Z2 and coupling condenser K2.
  • the valve V3 is similarly provided with a shunted biassing resistance G3 and resistance RC3 to provide the negative reaction.
  • the output is taken from valve V3 across the plate resistance Z3 through coupling condenser K3.
  • the stray capacities CI, C2 and C3 are shown connected to the valve VI, as before, by dotted lines.
  • the suppressor grid of VI is connected to the cathode of V2 as in Fig. 4 and the suppressor grid of V2 iscoupled to thecathode of V3 by an alternative arrangement involving a shunt resistance RS and a coupling condenser KS, which has been shown by way of example.
  • valve V3 occurs in a manner similar to' effect of the capacity in valve V2 corresponding to CI will be reduced by valve V3 in exactly the same way, because as before the resistance RC3 will be much smaller than the plate resistance Z2, and will not be affected by the alternative method of coupling the suppressor grid which has been shown.
  • the suppressor grid could also have been coupled to the cathode by other means such as. for example, by the use of a transformer.
  • the arrangement which have been described are also applicable to amplifiers inwhich the valves operate on the non-linear portions of the characteristics. such as are used for amplitying impulses.
  • the potential of the cathode of any of the valves follows substantially the correspondin grid potential and so also the preceding plate potential as soon as the impulse reaches a certain voltage; the circuit then operates as described.
  • the preceding circuits have been given only as examples, and various other means for connecting the suppressor grid in accordance with the invention can be imagined; for example, in an amplifier with feed-back.
  • the feed-back circuit can be used for transmitting the desired potentia to the su pressor grid.
  • a thermionic amplifier system comprising amplification means including a series of coupled amplifying stages having a tube in each stage, the first stage tube being a pentode, and means for at least partially neutraliz ng capacity between the pentode anode and ground, comprising potential-transmitting coupling between the pentode suppressor grid and a point in the amplifier system having an alternating poten tial of the same frequency and phase as the alternating potential of said anode and a maxi mum value at least eoual to the maximum value of said anode potential.
  • a thermionic amplifier system comprising amplification means including a series of coupled amplifying stages having a tube in each stage, the first stage tube being a pentode, and means for. at least partially neutralizing capacity between the pentode anode and ground comprising a potential-transmitting coupling between the pentode suppressor grid and a point in a subsequent stage having an alternating potential of the same frequency as the alternating potential on said anode, and of no lower peak value.
  • a thermionic amplifier system as set forth in 'claim 2 in which said suppressor grid is connected to the output of a subsequent stage.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
US435983A 1941-04-07 1942-03-24 Thermionic valve amplifier Expired - Lifetime US2416334A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB4613/41A GB548424A (en) 1941-04-07 1941-04-07 Improvements in or relating to thermionic valve amplifiers

Publications (1)

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US2416334A true US2416334A (en) 1947-02-25

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US435983A Expired - Lifetime US2416334A (en) 1941-04-07 1942-03-24 Thermionic valve amplifier

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US (1) US2416334A (pt)
BE (1) BE476622A (pt)
ES (1) ES177440A1 (pt)
FR (1) FR931784A (pt)
GB (1) GB548424A (pt)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2517863A (en) * 1944-10-12 1950-08-08 Darol K Froman Voltage supply circuit for vacuum tubes
US2538487A (en) * 1946-12-31 1951-01-16 Volkers & Schaffer Inc Self-focusing, direct-coupled, even stage amplifier
US2552809A (en) * 1945-08-27 1951-05-15 Decca Record Co Ltd Compensated amplifier circuit
US2934713A (en) * 1954-09-17 1960-04-26 Itt Anode-follower amplifier
US3061794A (en) * 1958-08-15 1962-10-30 Frank W Raucr Distortionless electrical amplifier

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2033274A (en) * 1933-04-07 1936-03-10 Bell Telephone Labor Inc Amplifier
US2145368A (en) * 1934-12-27 1939-01-31 Rca Corp Amplifier tube and circuit
US2154327A (en) * 1936-07-03 1939-04-11 Philco Radio & Television Corp Signal amplifier
US2212215A (en) * 1938-07-14 1940-08-20 Fides Ges Fur Die Verwaltung Electron discharge device

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2033274A (en) * 1933-04-07 1936-03-10 Bell Telephone Labor Inc Amplifier
US2145368A (en) * 1934-12-27 1939-01-31 Rca Corp Amplifier tube and circuit
US2154327A (en) * 1936-07-03 1939-04-11 Philco Radio & Television Corp Signal amplifier
US2212215A (en) * 1938-07-14 1940-08-20 Fides Ges Fur Die Verwaltung Electron discharge device

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2517863A (en) * 1944-10-12 1950-08-08 Darol K Froman Voltage supply circuit for vacuum tubes
US2552809A (en) * 1945-08-27 1951-05-15 Decca Record Co Ltd Compensated amplifier circuit
US2538487A (en) * 1946-12-31 1951-01-16 Volkers & Schaffer Inc Self-focusing, direct-coupled, even stage amplifier
US2934713A (en) * 1954-09-17 1960-04-26 Itt Anode-follower amplifier
US3061794A (en) * 1958-08-15 1962-10-30 Frank W Raucr Distortionless electrical amplifier

Also Published As

Publication number Publication date
GB548424A (en) 1942-10-09
BE476622A (pt)
FR931784A (fr) 1948-03-03
ES177440A1 (es) 1947-05-01

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