US2257570A

US2257570A - Neutralized system

Info

Publication number: US2257570A
Application number: US224063A
Authority: US
Inventors: Posthumus Klaas
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1937-09-11
Filing date: 1938-08-10
Publication date: 1941-09-30
Anticipated expiration: 1958-09-30
Also published as: GB500790A; BE430082A; DE734230C; NL57282C; FR843184A

Description

Sept. 30, 1941.

I K. POSTHUMUS NEUTRALIZED SYSTEM I Filed Aug. 10, 1938 Z'SheeLs-Shest 1 F/ZAMENT SUPPZ. Y MACH/NE 4 'i ru m BRI DGES ENVENTOR PGSLHUM ATTORNEY GRID SUPPZY Sept. 30, 1941. K pos umus 2,257,570

NEUTRALI ZED SYSTEM Filed Aug. 10, 1938 2 Sheets-Sheet 2 WIRE SYSTEMS I v ,4 \H./-'. arm/ 55 GRID I F/[AMENT SUPPLY SUPPLY INVENTOR ATTORNEY Patented Sept. 30, 1941 UNITED STATES PATENToFFIcE signor, by mesne assignmentato-Radio Corporation of America, New York, N. Y., a corporation of Delaware Application August 10, 1938, Serial No. 224,063 In Germany September 10, 1937 8 Claims.

This invention relates to a high frequency amplifier comprising neutralizing condensers for.

compensating the capacity between anode and grid of the discharge tubes available in the arrangement.

It is sought to design the arrangement in such manner that the neutralization is independent of the frequency, since otherwise there would be a risk of one or more spontaneously generated oscillations occurring in addition to the oscillations to be amplified. This result could always be obtained in arrangements, wherein the conductors connecting one or more electrodes to connecting points outside the tube have an inductance which may be neglected for the oscillations to be amplified.

In the case of short wave amplification, however, the obtention of suflicient stability involves serious difficulties, since for these short waves the inductance of the same conductors is not negligible. This applies more particularly for amplification of large quantities of energy for which water-cooled tubes are usually employed since it is necessary, in view of the size of the'tubes, to increase the length of the different conductors.

According to the present invention the desired effect is obtained by tuning the conductors, by which one or more electrodes are connected to connecting points outside'the tube and whose inductance is not negligible for the oscillations to be amplified, to the frequency of the oscillations to be amplified, and by inserting a damping resistance in the conductor through which the input impedance and the neutralizing oondenser(s) are connected to the grid, said damping resistance being shunted by a short circuit for the oscillations to be amplified. This short-circuit preferably consistsof the series connection of an inductance and a capacity which is tuned to the frequency of the oscillations to be amplified.

' The invention will be more clearly understood byreference to the accompanying drawings.

Figure 1 shows the diagram of connections of a well known neutralized amplifier comprising two push-pull connected discharge tubes.

Figure 2 is the substitution diagram of the arrangement shown in Figure 1.

, Figure 3 shows the same diagram of connections but embodies the improvement according to the invention.

Figure 4 illustrates an improvement of the arrangement shown in Figure 3, and

Figure 5 represents an arrangement compris-- ing an amplifying tube, according to the invention- In Figure 1, the cathode grid and anode of two push-pull connected discharge tubes are designated by K1, G1, A1 and K2, G2, A2 respectively. Between the grids G1 and G2 is connected an oscillatory circuit 3 to which are supplied the oscillations to be amplified and which is tuned to the frequency of the oscillations to be amplified. A circuit 4, which is also tuned to the frequency of the oscillations to be amplified, is connected between the anodes A1 and A2 of the tubes l and 2. The anodes A1 and A2 are connected to the grids G2 and G1 respectively through neutralizing condensers designated by C1 and C2. The cathodes K1 and K2 are interconnected through a conductor 5. For the sake of clearness the required feed sources are not represented in the drawings.

When using water cooled discharge tubes in the arrangement shown in Figure 1 the plates of the neutralizing condensers connected to the anode can be provided in the immediate vicinity of the anode, so that the conductors connecting the anodes A1 and A2 to'the connecting

points

01 and 02 may be made very short so as to have a negligible inductance to the oscillations to be amplified. However, the conductors 1 connecting the grids. G1 and G2 to the connecting points P1 and P2 respectively, as well as the cathode connecting leads 5 usually have such a length that the inductances of these leads are not negligible in amplifying ultra high frequency oscillations.

Figure 2 shows the substitution diagram of the arrangement represented in Figure 1, wherein the condensers between the point G1, K1, A1 and G2, K2, A2 respectively represent the inter-electrode capacities of the tubes I and 2 respectively. whereas the inductances 5, l, 8 represent the connecting leads between the two cathodes K1, K2 between the grid G1 and the connecting point P1 and between the grid 2 and the connecting point P2.

When the reactances of the inductances 5, I and 8 have a negligibly small value the arrangement shown in Figure 2 constitutes a Wheatstone birdge so that with a suitable size of the condensers C1 and C2 a tension set up between the points A1 and A2 cannot cause a tension between the points G1, K1 and G2, K2 respectively. When amplifying frequencies at which the reactances of the conductors and 8 are not negligible the equilibrium of the bridge is disturbed so that the desired neutralization is not ensured. Moreover, the conductor 5 is traversed by a current which, at these high frequencies, brings a considerable 5 potential difi'erence between the points K1 and K:

equal and opposite to the inductance of the coirductors. In this case the total reactance of each I of the

conductors

5, 1 and 8 will be zero for the frequency of the oscillations tobe amplified so included in the cathode lead of the corresponding tube. Consequently, the coil 20 in the grid supply conductor 1 of the tube l is coupled to a coil 22 inserted in the part of the conductor 5 between the point l4 and the cathode K1, whereas the coil 20 in the grid supply conductor 8 of the tube 2 is coupled to a coil 22 inserted in the part of the conductor 5 between the point l4 and the cathode K2. The maximum output energy is obtained by proportioning the coupling so that the coupling between the electrode supply conductors inside the tube is completely removed.

that complete neutralization canj'beachieved for" this frequency. For all other frequencies,'however, ther is no equilibrium in the bridge arrangement, so that additional'measures have to be taken for avoiding the spontaneous generation of oscillations having other frequencies, more particularly higher frequencies. According to the invention thismeasure; consists in inserting a damping resistance inthei conductors"! and' 8 through which the input. impedance and the neutralizing. condensersare connected to the grids, said damping resistancebeing bridged by ashortcircuit for the oscillations" to. b amplified.

Figure 3 shows a. circuit arrangement according to the invention which substantially corresponds to the arrangement shown in Figure 1', but which embodies. the improvements constituting the obj ectsof the invention" The conductor 1' between G1 and. P1 and conductor 8 between G2 and P2 include a series condenser 11 by means of which these conductors are tuned to the frequency of the. oscillations to be amplified. Furthermore, these conductors comprise a damping resistance l9 which is bridged by ashort circuit for the oscillations. to be amplified. This short circuit consists of'the series connection of an inductance 2B and a capacity 2| which are together tuned to the frequency of. the oscillations to be amplified. Furthermore, the connecting line 5. between K1 and K2 comprises condensers l5 and [6 by means of which each of th two parts. of this connecting line on either side of the connecting point [4 of the circuits 3 and dare tuned to the frequency of the oscillations to be amplified Of course, complete suppression ofany reaction, such as is ensured by the'arran-gement according to the. invention, causes a decrease in amplitude of the oscillations occur-ring in the circuit 4. To provide that. the amplification. is as strong as possibl it is consequently desirable in the arrangement according to the invention toavcid all influences that may'invol've a further decrease of the output voltage. One of these detrimental influences is the mutual induction between the. conductors that connect the electrodes of the amplifying tubes to connecting points outside the tube. In fact, this mutual induction causes a negative back coupling between the

circuits

4 and 3 thus causing a decrease of the output voltage.

According to. a further feature of the invention this detrimental influence is entirely or partly removed by providing that the inductance, which forms part of the circuiticonstituting. for the frequency to be amplified a short circuit of the damping resistance included in th grid cir-' cuit, is inductively coupled to the cathode lead.

Figure 4 shows one form of construction of an amplifying circuit according totheiinvention, wherein this arrangement. is used. Each of the inductances is coupled. to an inductance 22 1 Figure-5- showsan amplifying arrangement according toltheinvention which differs from the arrangerrrent represented in Figure 4 in that there is provided only a single amplifying tube I.

.The output. circuit 4 is connected between the anode and the cathode of the tube l and the grid is connected to one end of the input circuit 3 whose other end is connected through a neutralizing condenserCi to th anode. A point. on the input circuit 3 between the ends is connected to a point M of the cathode: conductor 5. In, this arrangement the electrode-supply conductors 5, II and I, are tuned, when necessary, by means of condensers l5, l8 and ll to the frequency of the, oscillations to be amplified, and the grid con.- ductor, 1 comprises a, damping resistance ['9 which is bridged by the series connection of a coil 20 and a condenser 2| tuned to the frequency of the oscillations to be amplified. The coil 20 is inductively coupled to a coil 22 inserted in the cathodeconductor 5.

The

coils

20 and 22 shown in Figures 3, 4, and 5 need only have a slnall self induction and will often consist only of a single turn.

,Iclaim2.

g1. Inanultra-high' frequency amplifying system, an electron discharge tube having an input electrode, a cathode and an output electrode, a highfrequency' input circuit, a high frequency output circuit, means series tuned to the frequency of said input circuit connecting said input circuit to said input electrode, a damping resistance in series-With said means, means connecting said output circuit to said output electrode, neutralizing'means coupling said input and output electrodes, and a circuit series tuned to the frequencyof operation of said high frequency input circuit connecting said cathode to said high. frequency circuits.

2'. In an ultra high frequency amplifying system, an electron discharge tube having an input electrode, a cathode and an output electrode, a high frequency input circuit, a high frequency output circuit, means series tuned to the frequency of said input circuit connecting said input circuit to said input electrode, means connecting said output circuit to said output electrode, neutralizing means coupling said input and output electrodes, a circuit series tuned to the frequency of operation of said high frequency circuits connecting said cathode to said high frequency circuits and a coupling between said series tuned circuit and said means series tuned to the frequency of said input circuit.

3. In a neutralized-amplifier comprising an electron discharge device having input and output electrodes including a cathode, high frequency input and output circuits connected with the input and output electrodes in said device respectively and aneutralizing circuit inter-connecting the said input and output electrodes, means for stabilizing said amplifier comprising means for tuning out the inductive reactance' in a connection between said circuits and an electrode of said device, means for reducing voltages of frequencies difierent than the frequency of operation of said circuits including a damping resistance in said connection and a circuit series tuned to the frequency of operation of said input and output circuits connected in shunt to said damping resistance.

4. A system as recited in claim 3 wherein said series tuned circuit in shunt to said damping resistance comprises a condenser and inductance.

5. A system as recited in claim 3 wherein the cathode of said device is connected to said circuits by a circuit series tuned to the frequency of operation of said circuit and wherein said last named series tuned circuit is coupled to the circuit in shunt to said damping resistance.

6. In a high frequency amplifier, an electron discharge device having input and output electrodes including a cathode, high frequency input and output circuits connected with the input and output electrodes in said device respectively, a neutralizing circuit connected between said input and output electrodes, a portion of said neutralizing circuit connection being common to the connection of said input circuit to said input electrodes, means for stabilizing the operation of said amplifier comprising capacitive means in said common portion of said connections for tuning out the inductive reactance in said connections, means for reducing voltages of all frequencies different than the frequency of operation of said input and output circuits including a damping resistance in said common portion of said connections and a circuit series tuned to the frequency of operation of said input and output circuits connected in shunt to said damping resistance.

7. A system as recited in claim 6 wherein said series tuned circuit in shunt to said damping resistance comprises a condenser and inductance.

8. In a high frequency amplifier, an electron discharge device having an input electrode, an output electrode, and a cathode, high frequency input and output circuits connected with the input and output electrodes in said device respectively, a circuit series tuned to the frequency of operation of said input and output circuits in a connection between said cathode and said input and output circuits, a neutralizing circuit connected between said input and output electrodes, a portion of said neutralizing circuit connection being common to the connection of said input circuit to said input electrode, means for stabilizing the operation of said amplifier comprising capacitive means in said common portion of said connections for tuning out the inductive reactance in said connections, means for reducing voltages of all frequencies different than the frequency of operation of said input and output circuits including a damping resistance in said common portion of said connections and a circuit series tuned to the frequency of operation of said input and output circuits connected in shunt to said damping resistance, and a coupling between said series tuned circuit in shunt to said damping resistance, and said series tuned circuit in said connection between the cathode of said tube and said input and output circuits.

KLAAS POSTHUMUS.