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Патент USA US2404188

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‘July 16, 1946.
'
w_ E, PHILUPS
NEUTRALIZED RADIO FREQUENCY AMPLIFIER
Filed Jan. 11, 1943
2,404,18
2,404,188
Patentecl July 16, 1946
UNITED STATES PATENT OFFICE
2.404.188
NEUTRALIZED RADIO-FREQUENCY
Willis
AMPLIFIER
Phillips, Deerfield, Ill., assignor to
Zenith Radio Corporation, Chicago, 111., a cor
poration of Illinois
Application January 11, 1943, Serial No. 471,960
'
13 Claims.
1
(Cl. 179—171)
2
which the neutralizing conductor and the neu
This invention relates to neutralized radio fre
quency ampli?ers and particularly to such am
tralizing condenser have no excessive voltage. ~
pli?ers which are employed at ultra-high fre
quencies, of the order of above thirty megacycles.
the invention will appear from the following de
It is well known that the electrodes of a therm
ionic tube, and particularly the plate and con
trol grid, have a de?nite capacity through which
the output and input circuits are coupled together.
To prevent excessive feed-back and regenera
tion, a neutralizing condenser having approxi
mately the same capacity as that existing be
tween the grid and plate is arranged to supply
an equal amount of energy of opposite phase
Other objects, advantages and capabilities of
scription of preferred embodiments thereof taken
in conjunction with the accompanying drawing,
in which:
Fig. 1 is a wiring diagram of a single tube ultra
high frequency ampli?er provided with a neu
10 tralizing circuit embodying my invention;
Fig. 2 is a similar diagram of a modi?ed form
of the invention;
Fig. 3 is a wiring diagram of an ultra-high fre
quency push-pull ampli?er provided with neu
of push-pull ampli?ers, the plate of each tube 15 tralizing circuits embodying my invention;
from the plate to the control grid. In the case
Fig. 4 is a diagrammatical view of a physical
embodiment of a high-power, ultra-high frequen
cy ampli?er constructed in accordance with the
When such conventional circuits are embodied
wiring diagram of Fig. 3, and
in ultra-high frequency ampli?ers, considerable
di?iculties are experienced. This is particularly 20 Fig. 5 shows an alternative speci?c connection
in the arrangement shown in Figure 3.
true where large tubes are employed because the
Referring to the drawing and particularly to '
neutralizing leads or conductors have, in that
Fig. 1 thereof, the reference numerals Ill and H
case, and particularly in the case of push-pull
designate the inductance and tuning condenser
ampli?ers, to be of a length which is a substan
tial fraction of the wave length. At ultra-high 25 of the input circuit which is connected to the
control grid !2 of the thermionic tube [3. _The
frequencies the neutralizing conductor has a very
plate I4 of the tube 13 is connected to one termi
substantial reactance and the neutralizing con
nal of the tuned circuit l5 which has its other
denser and the neutralizing conductor have a
terminal connected by a by-pass condenser IE to
very large distributive capacity to ground, a ca-.
the cathode H. A source of high voltage I8 is
pacity which may approach that of the neutraliz
connected to the junction point of circuit l5 and
ing condenser itself.
condenser H5. The .plate [4 is connected through
I ?nd that in some cases the neutralizing con
a neutralizing condenser I9 to a conductor 2tv
ductor and the plate of the neutralizing con
which is connected to the low side of the in~
denser to which it is attached acquire very high
voltages. _In some cases, the condenser arcs over, 35 ductance it. The conductor 26 has at ultra
high frequencies a relatively high reactance
and arcs extend out of the conductor and into
which is illustrated by the coil 2|. The react
the air. This
voltage may become so large
ance may attain very high values and conse
in high-power ultra-high frequency ampli?ers as
quently it is shown as a full line coil 2! notwith
to be the limiting factor in determining the max
imum power that may be produced by such an 40 standing-the fact that the conductor 29 is a solid
is usually connected through a neutralizing con
denser to the control grid of the other tube.
piece of copper.
.
amplifier. Furthermore, the input tuned circuit
In Fig. 1 I illustrate as the capacity 22 the
is effectively shunted by the inductance of the
distributive capacity of the conductor 20 and the
neutralizing conductor and the distributive ca
plate of the condenser l 9 to which it is attached.
pacity of the conductor and the neutralizing con
denser so that the inductance of the input circuit 45 This distributive capacity provides a low react
ance path at ultra-high frequencies. The value
must be seriously limited. In many cases, it is
of capacity 22 may approach the value of the
found that even though the capacity of the in
neutralizing condenser is and consequently it is
put circuit be eliminated it is not possible to tune
shown in full lines as a condenser.
the input circuit to the ultra-high frequency to
50 In accordance with the present invention I
which it is desired to operate the ampli?er.
connect an inductance 23 between the conductor
The principal object of the invention is to
2!] and the plate of the condenser l9 to which it
provide a neutralized ultra-high frequency am
is attached and ground. This inductance 23 may
pli?er in which these disadvantages are obviated.
be of the order of a few microhenries.
A further obiect of the invention is to provide
I have found that the objectionable high volt
a neutralized ultra-high frequency ampli?er in 55
aeoaiss
3
4
age produced in the conductor ‘.20 and in the plate
of the condenser id to which it is attached results
from the fact that the inductive reactance 2|,
denser it closely approximates the capacity be~
tween the plate l4 and the control grid I2.
together with the capacitive reactance Z2, consti
tutes, at ultra-high frequencies, a series resonant
circuit. My introduced inductance 23 destroys
this ‘series resonant circuit. Preferably it consti
which my invention is embodied in a push-pull
ampli?er provided with neutralizing circuits ex
tending from the plate of one tube M to the con
trol grid of the other tube i2. Each neutralizing
tutes, with thedistributive capacity 22, aparallel
circuit comprises a neutralizing condenser [9
resonant circuit which’has a high resistance to
connected to the plate of one tube, which neu
In Fig. 3 I have shown a preferred manner in
the ultra-high frequency current. That is, the .10 tralizing condenser is connected by a conductor
inductance or inductor 23 is connected in parallel
Zii to the grid of the other tube. Here again the
with the distributive capacity 22 of ‘said conductor
inductive reactance of the conductor 20 is illus
20 and condenser l9 and one terminal of induct
trated as a coil 2i and the distributive capacity
ance 23 is connected adjacent the .juncticn .of
‘of each conductor .23 and the plate of the con
conductor 25) and condenser l9. 'Before‘theintro 15 denser; E9 to which .it is attached is illustrated as
duction of my inductance 23, a large resonant cur
aicapacityzl
rent ?owed from the conductor 2Q :to ground,
.This.circuit is preferred for high-power, ultra
through the easy path provided by the distrib
high-frequency ampli?ers since the neutralizing
utive capacity 22, and this high current resulted
circuits can be kept relatively short. Neverthe
in the excessively high voltage of the conductor 20 less, since the tubes used/must be physically large
Z?andof “the plate of 'the condenser ill to which
for high-power ‘ampli?ers, the conductors 29
havesubstantial length an'd'objectionable ‘high
the conductor ‘dais-connected. The parallel res
onant‘cir'cuit 22,23 cuts down‘this ultra-high fre
voltages are‘ found onthese‘con'ductors and onfthe
plates'of'the condensers to'which'they are con
quenoy'current to aluminium, and thus the ob
jectionable high voltage is destroyed.
25 nected. "Itfwill-be'understood that the objection
able high voltage increases with increase of‘fre
‘The'inductance value of the inductor23is best
quency.
determined practically. Thus I introduce'an in
ductor'23 which is obviously too large and ‘I ad
In ‘this case, in ‘Fig. 3‘also,'I‘may correctthe
circuit by connecting a'coilf23 between each .con
'ju'st‘ thecondenser l 9 for optimum neutralization.
I determinethe‘voltage of the conductor 20 and
denser '99 ‘and ground .in the ‘manner described
above in relation to Figs'l and 2. In practice,
the 'plate "'of'the “condenser 59 to which it is at
tached. In high-power installations I may con
however,‘ I prefertto connect arsingle :inductor‘23'
tact’th'e plate of ‘the condenser lg'with a‘metal
between .t‘hetwoxcondensers L9, ‘in "the f manner
shown in. Fig. '3. The center of itheindu'ctor' 23'
rod held on ‘an insulating "handle. On‘with
drawing the‘rod'an varc'will extend between the
isagneutral'orrzero point and it'may'be ‘grounded
‘condenser l9 and the ‘end of the rod, owing to
‘the ‘objectionable ' high voltage. "By progressively
decreasing the inductance value of the inductor
if desired.asshown..inili‘igure?. It is thus seen
iromzh‘iguresitl and '5 that the inductor?ll’ may
constituteeithena single inductor'or in ‘effect two
23 I ?nd that the are which can thus be v‘drawn
inductors :for achieving "the purposes ‘of the
becomes‘lessand less, and the ?nal steps of ad 40 present; invention. ‘ The ’ steps ‘of determining the
proper.‘inductancevalue 'of the inductor ' 2.1%’ ‘are
justment maybe-performed with the aid of a glow
the same 'asxpreviously ‘described. In ‘the *final
vlamp'untiLrwhen I have an inductor 2-3 of the
condition of: adjustment each/condenser l9‘ is'ad
‘correct‘inductance value,'no excessive voltage can
justed to correspond to the plate ‘to grid .capacity
'be'discovered ‘on the-plate of‘ the condenser I 9' to
~which .the ' conductor '20 is attached. When that 45 of‘the tubesandeach half of the inductor .23’
constitutes, “with :the adjacent capacity :22, ‘a
end is attained, the distributive capacity 22 and
‘the “inductor 23 are believed to constitute a
.qllenCY
parallel resonant circuit ‘ at : the .ultraehigh
‘parallel resonant-circuit ‘at the ultra-high fre
'quency. As‘the value of inductance 23' is progres
sivelydecrease'd; the ‘capacity of the condenser l9
InFig, 4.: show diagrammatically a physical
embodiment of a ‘high-power, ultra-high “free
has to ‘:be "progressively ‘increased - to provide
. quency ampli?er constructed; in. accordance'iwith
:proper neutralization. When ' set ‘correctly, ‘the
condenser l9 has a capacityapproximately-equal
to that "existing between the grid izvand the
plate l4.
'
‘In Fig: 2 Iihave shown the wiring-diagram em
the wiring diagram of Fig. 3.‘ This amplifier
comprises two;high»power, water-cooled triodes
it ‘which include two ‘depending copper cylinders
Zia-which; are bridged across by-a metal bar 25 to
which .thehigh'voltagesourcetla is connected by
means of acon'ductor ~2i'igthe cylinders 24 being
connected to the plates of the tubes. The‘output
tuned circuit- t5. is constituted by adjustable con
ingcondenser 19 ‘has one of its terminals con
nected to‘the 'low‘end'of the'output tuned'circuit 60 denserplates-?l', a metal bar 23 slidably vmounted
onthe cylinders?kand a swingable loop or stirrup
l5 and its other terminal connected by‘means'of
29 -connected.tothe output leads ~30. The neu
a'conductor '25] to the control grid 92 through
tralizingcondensers ware constituted by arcuate
the ‘unnumbered condenser. vIn this case the in
plates .135 which are aadjustably. mounted so that
ductive'reactance of the conductor 20 is illus
they can be broughtinto proper spaced relation
trated as the coil 2! and the distributive capacity
with cylinders :26. The Iarcuate ‘plates 3| are
‘of ‘the "conductor 29 and the plate of the con
connected by'the conductors-20 togridterminals
denser I'EJ to‘which it is‘ attached is also illustrated
of .the tubes 13, the conductorsrbeing arranged
as the capacity‘22.
CZ‘iSS'rClTOSS fashion andinvspaced relation. The
My introduced-inductor 23 has one of its‘ter
minals- connected to the plate of the condenser 70 inductor“l is constituted bytwometa1 bars:32,
the ends of whichiareiconnectedto the-grid .con
I9 to~which the ‘conductor 2!] is connected and
nectors of the tubes. Thei'barsr 32 are bridged,
its other-terminal connected to ‘ground. At the
final adjustment'the inductor 23 constitutes With
remote from these ends, by a metal iblock 33Jar~
the capacity'ZZ ‘aparallel circuit ‘resonant at the
ranged~ to establish desired induct-ance {for the
ultra-‘high frequencyand the capacity of the con 75 inductor Iii. The capacitorll is'constitutedsby
bodying "my'in‘vention in another conventional
neutralizing circuit. In this'circuit the neutraliz
2,404,188
5
6
an adjustable grounded plate 34 arranged to
tween the other said condenser and its associated
move between the bars 32 to provide proper tun
ing capacity for the grid circuit. Grid energy is
supplied to the inductor ID by means of a loop
35 arranged immediately below the bars 32. Fila
ment energy is provided by the coaxial lines 36,
the interior conductor being connected to one
?lament terminal on the tube I3 and the outer
conductor.
izing conductor which develops excessively high
a stout copper wire formed with a few coil turns
5. A neutralizing circuit including a neutral-.
izing condenser and a. neutralizing conductor, said
'
4. In an ultra-high frequency power ampli?er
including a neutralizing condenser and a neutral
voltages as a result of the reactance of said con
ductor at ultra-high frequencies, the combina
tion of an inductor of substantially no resistance
in parallel with said conductor and ‘connected to
conductor being connected to the other ?lamem
a point of excessive high voltage, said conductor
10
terminal of the tube l3.
having sufficient reactance to diminish substan
The inductor 23' is connected between the two
tially said excessively high voltage.
plates 3|. This inductor may take the form of
depending upon the necessities of the installation.
In practical cases it may have an inductance of 15 condenser and conductor having a substantial
a few microhenries, which is su?icient at ultra
high frequencies to provide a high reactance.
distributive capacity and said conductor having
sufficient length whereby at ultra-high frequen
cies said distributive capacity and the impedance
Thus, at 50 megacycles one millihenry has a re
of said conductor tend to constitute a resonant
actance of more than three hundred thousand
ohms, and ordinarily a mere fraction of that in 20 circuit with the production of excessively high
voltages on said condenser and conductor, in
ductance is sufficient to provide the desired effect.
combination with an inductor of sufficient react
It will be noted that in the single-tube am
ance connected adjacent the junction between
plifler shown in Figs. 1 and 2 the input tube
circuit I0, H is shunted by the tuned circuit 2!,
22 in the absence of the added inductor 23. In
some cases,
even with a very small inductance
l0 and the omission of a physical condenser H,
it is impossible to get the frequency su?iciently
said condenser and conductor to provide with said
distributive capacity a parallel resonant circuit at
said frequencies whereby the ?rst said resonant
circuit is effectively destroyed and the excessively
high voltages resulting therefrom are prevented.
6. A neutralizing circuit including a neutral
high. The provision of the added inductor 23 or
23’ as the case may be greatly reduces the shunt 30 izing condenser and a neutralizing conductor hav
ing a substantial distributive capacity and said
loading across the tuned circuit and permits a
conductor having suf?cient length whereby at
more favorable ratio of L to C and allows the
ultra-high frequencies said circuit resonates, pro
ampli?er to be operated at a higher frequency.
ducing excessively high voltages therein, and a
Furthermore, the loading of the plate tuned cir
reactor of substantially no resistance connected
cuit 15 by the shunting effect of capacities is
to said circuit adjacent the junction between said
and 22 is reduced by the provision of the induc~
condenser and conductor for effectively destroy
tor 23 permitting higher frequency operation and
ing
the resonance thereof and effectively nullify
reducing losses in the tank circuit H5. The same
ing said excessively high voltages.
effects are attained in the push-pull circuit shown
'7. In a push-pull, ultra-high frequency power
in Fig. 3 and illustrated in Fig. 4.
40
ampli?er
including a pair of thermionic tubes, a
Although the invention has been described in
pair of neutralizing condensers and neutralizing
connection with details of speci?c embodiment
conductors connecting the plate of each tube to
thereof, it must be understood that such details
the control grid of the other tube, each condenser
are not intended to be limitative of the invention
and conductor having a high distributive capacity
except insofar as set forth in the accompanying
and each conductor having sufficient length
claims.
whereby each conductor and its condenser tend
I claim:
to resonate at ultra-high frequencies, producing
1. In an ultra-high frequency power ampli?er
excessively high voltages therein, and a reactor
including a thermionic tube and a neutralizing
condenser and a neutralizing conductor for sup 50 of substantially no resistance connecting points
adjacent said condensers whereby the tendency
plying plate energy to a control grid, the com
to resonate and to produce ultra-high frequencies,
bination with said neutralizing elements of an
is effectively nulli?ed.
inductor of substantially no resistance arranged
8. In an ultra-high frequency power ampli?er
in parallel with the distributive capacity of said
circuit,
including at least one thermionic tube
conductor and condenser and connected thereto
adjacent their junction.
2. In a push-pull ultra-high frequency power
ampli?er including a pair of thermionic tubes, a
having plate and grid and a neutralizing con
denser and a neutralizing conductor for supplying
plate energy to said grid, the neutralizing con
denser being adjacent a plate and the neutraliz
pair of neutralizing condensers and neutralizing
ing conductor being relatively long, and an in
conductors connecting the plate of each tube to
the control grid of the other tube, the combina 60 ductor of substantially no resistance in parallel
to said conductor connected adjacent the junc
tion with said neutralizing elements of an induc
tion of said conductor and said condenser.
tor arranged in parallel with the distributive ca
9. In a push-pull, ultra high frequency power
pacity of each conductor and condenser and con
ampli?er, including a pair of thermionic tubes, a
nected adjacent the junction of each conductor
pair of neutralizing condensers adjacent the
and its condenser.
plates of said tubes and relatively long neutraliz
3. In a push-pull ultra-high frequency power
ing conductors connecting the neutralizing con
ampli?er including a pair of thermionic tubes,
denser of one tube to the control grid of the other
a pair of neutralizing condensers and neutraliz
tube, and an inductor of substantially no resist
ing conductors connecting the plate of each tube 70 ance connecting said conductors adjacent their
to the control grid of the other tube, the com~
junction with their associated condensers.
bination with said neutralizing elements of an
10. In a push-pull ultra high frequency power
inductor connecting a point adjacent the junction
ampli?er including a pair of thermionic tubes, at
between one said condenser and its associated
conductor to a point adjacent the junction be
least one neutralizing condenser and one neutraL
75 izing conductor connecting the plate of each tube
2,404, 18.8
‘tothe;controlgridpf 'th_etotliertube,-1thew combina
plying plate energy to a control grid, the combi
nation with said neutralizing elements of an in
tion with said neutralizing elements 30f ;.an;in
;ductor_ connected in parallel with the distributive
capacity of said conductor and .condenser and
connected adjacent the junction of;said conductor
ductor ,arrangedin parallel with the vdistributive
capacity of said conductorandcondensensaid
inductor and distributive capacity comprising ‘ele
ments of a-parallel tuned circuit tuned to said ‘de
sired frequency,
and said condenser.
11. In a push-pull ultra high frequency- power
ampli?er including ,a pair of thermionic tubes, a
'pair of neutralizing “condensers and neutralizing
13. In a push-pull ampli?er including a pairof
thermionic tubes operable at a desired frequency,
conductors connecting the- plate of teachi‘tube to 10 at least one neutralizing condenser'and ,one neu
the control grid of‘ the other tube, ‘the combina
tion with said neutralizing elements of one in
tralizing conductor connecting the plate of each
tube to the control grid of the other tube, the
combination With said neutralizing elements of
an inductor connected in parallel With the ‘dis
tributive capacity of said conductor and con
denser, said inductor and distributive capacity
comprising elements of a parallel tuned circuit
tuned to said desired frequency.
WILLIS E. PHILLIPS.
ductor'arranged ‘in-‘parallel with the distributive
capacity of ‘one :of said conductors and one of
said .condensersand connected adjacent the junc
tion ofv said one conductor ‘and said ‘one con
denser.
12. In. an ampli?er-including a thermionic tube
operable at-a desired frequency and a neutralizing
condenser and a neutralizing conductor for sup
20
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