US1768182A - Thermionic valve circuits - Google Patents

Description

June 24, 1930. P. w. WILLANS THERMIONIC VAL E CIRCUITS Filed April 5, 1926 2 Sheets-Sheet 1 June 24, 1930. P. W; WILLANS 1,768,182

THERMIONI C VAL E CIRCUITS Filed April 5, 1926 2 Sheets-Shee P Patented June 24, 1939 PATENT @FflQE PETER WILLIAM VVILLANS, F PAT'IISHALL, TOWGESTER, ENGLAND THERMIONIC VALVE CIRCUITS Application filed. April 5, 1926, Serial No. 99,944, and in Great Britain April '7, 1925.

This invention relates to, and has for its object the provision of improvements in, thermionic valve circuits; More particularly the invention relates to thermionic valve circuits in which means have been provided for neutralizing the capacity coupling between the grid and plate circuits of the valve. Means for this purpose have beenheretofore proposed comprising what is essentially a transformer and a capacitative device, the

transformer having one of its windings connected between the plate and the filament system. of the valve and the other winding connected between the grid and the filament system of said valve and the capacitative'device being connected in series with either of'said windings. In order for this arrangement to function it is necessary that the coeflicient of coupling between the transformer windings shall be unity and that the number of turns of the former and latter windings shall bear the same ratio to one another as the capacity to be neutralized bears to the capacity of said capacitative device, or in other words that the ratio of the turns shall be-in the inverse ratio of the associated capacities.

The object of the present invention is the provision of improved means for neutralizing the capacity coupling of a thermionic valve and the invention consists broadly in the arrangement according to which the capacitative device in an arrangement such as the above constitutes the major part of the effective capacity across an inductance to which the valve is connected. The capacity of this device will be not less than .00005 micro farads.

In accordance with this arrangement it is not necessary to have the coeflicient of coupling substantially equal to unity nor to have the ratio of the turns of the transformer windings in the inverse ratio of the associated capacities. In cases where the capacitatlve device is connected in series with the trans former winding system, which is connected between the grid and the filament system, the aforesaid inductance across which said capacitative device is connected is the grid circuit inductance.

In cases where said capacitative device is connected in series with the transformer winding which is connected between the plate and the filament said inductance is the plate circuit inductance.

The said capacitative device may in some cases be constituted by the variable capacity condenser by which the aforesaid inductance is adapted to be tuned but in this case the mutual inductance between the transformer winding must be variable. other condenser of smaller capacity may be connected across said inductance for tuning purposes.

Preferably however the tuning is effected" by a variation in value of the aforesaid mutual inductance with or without the small additional condensers. The essential feature is that the said capacitative device constituted as above stated the major part of the effective capacity across said inductance.

The transformer winding other than that in series with which the capacitative device is connected preferably constitutes either the grid circuit inductance or the plate circuit inductance according as whether the capacitativedevice is connected, as above described, across the plate circuit inductance or across the grid circuit inductance. It will therefore be seen that in one simple embodiment the invention simply. consists in connecting, in series with either the anode or grid circuit condenser of an ordinary receiving set, a coil which is magnetically coupled to the grid or anode circuit inductance.

In order that the invention may be more I clearly understood certain embodiments thereof are illustrated respectively in the accompanying Figs. 16 and the same will now be described it being understood that the particular arrangements illustrated are susceptible of various modifications'without departing from the scope of the invention as defined in the appended claims.

In all the drawings L and L are the transformer windings, A is the capacitative device and I is the inductance across which said capacitative device is connected. In each case L is thewinding in series with which the capacity A is connected.

Figure 1 illustrates a simple case in which If desired anthe winding L constitutes the grid circuit inductance and the inductance I the plate circuit inductance. In this case the condenser A and winding I; are connected in series between the plate and filament i. e. across the inductance I and high tension battery II. T. The condenser A preferably con stitutes the entire capacity across the inductance I but a second condenser B of less capacity may be connected across said in;- ductance I'for the purpose of tuning.

Figure 2 illustrates a simple case in which the winding L constitutes the plate circuit inductance and the inductance I the grid circuit inductance. In this case the condens 3 A and the winding L are connected in series as shown between the grid and the side of the high tension battery H. T. which is remote from the filament. As in the case of Figure 1 the condenser A may be the entire capacity across the coil I or a second condenser B of smaller capacity may be pro-- vided.

Figure 3 illustrates a case in which the winding L constitutes the grid circuit inductance and the inductance I the secondary of the plate circuit transformer. In this case the series connection of the winding L and the condenserA between the plate and the filament is inductive instead of. direct. .Thus the winding L and the condenser A are connected, as shown, together with the inductance I in a closed circuit extending from and returning to the filament the said inductance I being coupled to the primary I of the plate circuit transformer. If there is a condenser B across the inductance I in this case it will have the eifect of throwing capacity across the inductance I according to well known transformer theory. If how" ever we reckon the total effective capacity across the inductance I, the condenser A constitutes the major part of this effective capacity.

It will be appreciated that an, arrangement similar to that shown in Figure 3 but on the basis of Figure 2 instead of Figure l i. e. with the inductance I constituting the grid circuit inductance and the winding L the plate circuit inductance instead of vice versa) may be easily provided if desired. Special illustration and description of such arrangements has not been deemed necessary.

In some cases either the inductance coil I or theneutralizing transformer windings L or I1 may be connected indirectly to the appropriate electrodes through the medium of a condenser. Thus in Figure 4 is shown an example of' an arrangement wherein the windingL is connectcd'to the grid through the medium of a condenser C. In this case the inductance coil I constitutes the plate circuit inductance, the winding I is connected in the plate circuit of a preceding valve and the winding I1 and neutralizing condenser A is connected preferably has an impedance which is small (for the frequencies being received) in comparison with that of said condenser A. As only a small coil is necessary for this purpose no specially designed apparatus is required and as capacity effects in such coils are negligibly small, the circuit can be satisfactorily operated over a'widc range of frequencies. I

In any of the above cases moreover the condensers and/ or inductances may be vari-' able. For example I may tune the inductance I by varying the capacity of the condenser A and at the same time varying the mutual inductance between the windings L and L Preferably the anode circuit is tuned by variation of its'inductance. In 'an'- important appllcation of the lIlVGIltlOIlhOW ever, viz., the capacity coupling neutralization of the intermediate frequency amplifier of a supersonic receiver, no tuning adjustments are required as the amplifier operates on a fixed band of wave, length.

When the anode. circuit is fixed by varying its inductance and the grid circuit by varying its capacity the neutralizing coupling may be efi'ecte-d by a plug-in coil assembly comprising both the grid circuit inductance and the neutralizing inductance. The fixed coupling' is suitable in this case for any range of wave-lengths for which the grid circuit inductance is suitable, the coil assembly beinginterchanged when necessary for another with correctly proportioned windlngs. In some cases this coupling device may consist of a single coil wit-h a suitable tapping point. I

In some cases the invention may be combined with other forms of retroactive coupling in order to obtain greatersensitivity. In particular I may apply any form of retro-- active coupling to the anode circuit for the purpose of reducing its damping, the neutralizing coupling enable this effect tobe obtained without the aerial circuit damping being reduced. The load on the anode circuit due to the internal resistance of the valve may thus be counteracted without the tem becoming self oscillatory. This'res'ults in greatly enhanced sensitivity and selectivity.

The transformer in the drawings is shown as having two windings connected in se ies. It may thus convenientlyconsist of a single tapped coil. Alternatively the two windings may be quite separate. For example one may be connected to the filament and the other to the high tension positive.

The invention may be applied to a receiver in which there are a number of stages of amplification connected in cascade. Two examples of three stage amplifiers having capacity coupling neutralization in accordance with the invention are illustrated in Figures 5 and 6.

The connections in these figures are shown in a conventional manner and are deemed clear from the drawing. The figures therefore will not be described in so far as description is necessary to show how the same are comprised in the present invention.

The three stage amplifier illustrated in Figure 5 is on the basis of Figure 1; that is to say the inductances I are on the plate circuits and the windings L of the transformers are in the grid circuits. Considering the second valve from the left it will be seen that the parts L L A, I and C are related there to and function with respect thereto in subvalve from the left but that the inductance I, which constitutes the plate circuit inductance of said second valve, functions in re spect of said thlrd valve in the same capaclty as does the transformer winding L in respect of the second valve. For the rest the drawing is deemed sufiiciently explicit.

The amplifier illustrated in Figure 6 is on the basis of Figure 2; that is to say the inductances I are in the grid circuits and the windings L are in the plate circuits.

Considering the second valve from the left it will be seen that the transformer winding L is connected through the high tension battery H, T. across the plate and filament. The condenser A and transformer winding L are connected in series through a condenser C and the high tension battery H. T. across the grid and filament. The inductance I is connected in parallel with said con- 3: denser A and winding L i. e. is connected across the grid filament through the condenser C and high tension battery H. T.

In this case also it will be quite clear from the drawing that similar parts are similarly related with respect to the third valve from the left but that the transformer winding L functions in respect to said third valve in the same capacity as does the inductance I in respect of said second valve.

What I claim and desire to secure by Letters Patent is 1. Apparatus for neutralizing capacity coupling between the grid and plate circuits of a thermionic valve comprising a transformer, a capacitative device and an inductance, said transformer having one of its windings connected between the plate and the filament system and the other winding between the grid and the filament system,

said capacitative device being connected in series with one of said windings and, together with said one winding, across said inductance, said capacitative device moreover having a capacity of the order of ten or more times the capacity between the plate and grid of the thermionic valve and constituting, with said inductance and said latter winding, a resonant oscillatory circuit, tuned to the required frequency of which it is the dominating capacity.

2. Apparatus for neutralizing capacity coupling between the grid and plate circuit of a thermionic valve, comprising a transformer, a capacitative device and an inductance, said transformer having one of its windings connected between the plate and the filament system and the other winding between the grid and the filament system, said capacitative device being connected in series with one of said windings and, together with said winding, across said inductance, said capacitative device moreover having a capacity of the order of ten or more times the capacity between the plate and grid of the thermionic valve and constituting the variable capacity condenser by which said inductance is adapted to be tunedto a variety of frequencies.

3. Apparatus for neutralizing capacity coupling between the grid and plate circuits of a thermionic valve comprised in a multi stage amplifier, comprising a transformer a capacitative device and an inductance, said transformer having one of its windings connected between the plate and the filament system and the other between the grid and the filament system the former of said wind ings being also in circuit with an adjacent valve, said capacitative device being connected in series with one of said windings and,

together with said winding, across said inductance, said capacitative device moreover having a capacity of the order of ten or more times the capacity between the plate and grid of the thermionic valve and constitut- In witness whereof I atfix my signature. 3

PETER WILLIAM WILLANS.

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