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Патент USA US2119315

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'May 31, 1938.
'
w, BUSCHBECK _
2,119,315
NEUTRALIZING CIRCUIT FOR SCREEN GRID TUBES
Filed April 3, 1935
'
2 Sheets-Sheet 1
(‘.4 77-1005
(OI/7190!
ourpw~_+
INPUT
' INVENTOR
‘
WERNER BUSCHBECK
BY
“
>
ATTORNEY
'
'
May 31, 1938.
w. BUSCHBECK
2,119,315
NEUTRALIZING CIRCUIT FOR SCREEN GRID TUBES‘
129. 5A
Filed Alz‘fil 3, 1955
2 Sheets-Sheet 2 ‘
INVENTOR
WERNER BUSCHBECK
‘BY
WM’
ATTORNEY
Patented May 31, 1938
2,119,315
UNITED . STATES
PATENT ‘OFFICE
2,119,315
' NEUTRALIZIN
CIRCUIT FOR SCREEN-GRID
TUBES
Werner Buschbeck, Berlin, Germany, assignor to
Telefunken Gesellschaft fiir Drahtlose Tele-'
graphie m. b. H., Berlin, Germany, a corpora
tion of Germany
Application April 3, 1935, Serial No. 14,494
In Germany April 3, 1934
4 Claims.
The present invention is concerned with ways
and means adapted to neutralize or compensate
residual capacitances existing , in screen-grid
tubes between the control electrode and the
5 plate, and which are especially suited for short
Wave. systems.
‘
Owing to the presence of the’ screen-grid‘ the
capacitance existing between plate and control
electrode is effectively diminished. The residual
10 capacitance which may remain is neutralizable
with such means as are known from triode tubes
as long as this assumption is ful?lled; that the
screen-grid so far “as alternating “current‘volt
age is concerned is at cathode potential. And
this assumption may be suppo‘sed'tb belpracti
cally satis?ed where not unduly high tube ca
pacities are dealt with, where the waves are ‘long,
and where an adequately high blocking condens
er is provided between the screen grid and the
cathode.
Where‘ however shorter waves are
concerned, and ‘where screen-grid tubes are de
screen-grid and the cathode (Ls) to secure per
fect neutralization for a very de?nite wave
length. However, such neutralization is inade
quate in practical working inasmuch as it would
be lost and lacking as soon as there is a change
in the wave-length, while the restoring of the
state of neutralization would be attended with a 10
good deal of tedious and time-consuming read
justment in every given instance. The ‘present
invention, therefore, discloses ways and means
incorporated in a circuit organization whereby
neutralization of the residual capacitance be 15
tween control grid and plate will be insured un
der conditions unaffected by the wave-length or
frequency.
According to the invention, by the simulation
of all of the capacitances existing inside the tube, 1'
is no longer satis?ed. ' Of necessity, the connect
ing leads between the‘ electrodes and the lead
missible‘to disregard the capacities existing be
in points or seals across the vacuum vessel (with
tween plate and cathode, or between screen-grid ‘
the exception of the plates in water-cooled tubes)
and cathode,>which anyway are always inherent
are of a certain length and thus have an induc
ly small.
tive reactance which," where short-waves are
involved, is no‘ longer negligibly small in com
basic idea of the invention are shown in the ac
.
25
‘
A number of exempli?ed embodiments of the
parison with the capacitive reactance residing
in‘ the correspondingintermediate-electrode ca--v
companying drawings, wherein Fig. 1A is a 30
screen-grid circuit neutralizing arrangement ac
pacitances. Even if the supposition were ‘made
that the‘ capacity interposed between the screen
cording to the invention; Fig. 1B is a circuit
equivalent, to that shown in Fig. 1A, but redrawn
. grid and the cathode were free from loss (leak
3
present a relative phase angle of 180 degrees, ‘
it ispossible by choosing suitable dimensions or
values for the inductance existing between the
a point corresponding to the screen-grid itself is
created, whence neutralization is e?ected. Un
der certain circumstances, it may here be per
signed for large powers,'the said assumption
or?
(C1. 179--171)
age) and in?nitelyhigh, the screen grid can no
longer be considered,‘ as regards high-frequency,
to be at cathode potential. However, this means
that in the case of the arising of a plate alter
nating voltage, there is impressed upon the
40 screen-‘grid an alternating voltage of the same
frequency, but: a phase ‘displacement angle of
180 degrees, the amplitude of which’ is' governed
by the voltage division due to the capacitance
‘(Cs'A) prevailing between the screen-grid and
4 01 the plate, and the lead inductance (Ls) existing
between» the screen-grid and the cathode. In
other words, the screen-grid, so iaras the con
trol electrode‘is concerned; acts like a further
anode or plate; which, to ‘be sure, is subject to
‘alternating voltages" ‘of lower amplitude, but
which because ofthe ‘considerable capacitybe
tween ‘the screen-gridand the control electrode
(Cos) is in‘ rather close coupling relation with
the‘ latter. In view of the fact that the alter
in a different form; Fig. 2 is a similar form of
circuit as shown in Fig. 1B utilizing tubes in 1
push-pull according to the invention; Fig. 3A is _
a modi?cation of the’ arrangement shown in
Fig. 1A, but employing grid-circuit neutraliza
tion, and Fig. 3B is an equivalent and redrawn
circuit.
Referring in particular to Fig. 1A, a stage of
ampli?cation is shown as comprising a screen
gri-d tube V whose cathode is denoted by K, the
control grid by G,‘ the screen-grid by S,‘and
the plate or anode by A. The plate potential, by
ways and means known in the art, is supplied by
the aid of a radio frequency choke coil D, while
the plate oscillation circuit LCC is relieved of
direct voltage by the provision of ‘a blocking
capacity B. The radio frequency control voltage
is impressed upon the grid circuit across the
terminals I] and I. The screen-grid potential is
furnished from a source of voltage Else. The in
ductances of the'leads or wires brought to the
jnating voltages at the plate and the screen-grid ‘ various electrodes, in which‘are ?gured also the
2
2,119,315
leads disposed inside of the vacuum vessel, are
indicated in the form of lumped inductances
Lo, Ls and LK. According to this invention, neu
tralization under conditions independent of fre
quency or wave-length is secured by the fact
that all of the capacitances existing within the
tube as well as the inductances of the leads
brought to the different electrodes are simulated;
in fact, such simulation, as it were, constitutes a
10 homologous complement of the tube V including
all of the leads and wires.
The neutralizing action of Fig. 1A may be more
readily understood by reference to Fig. 1B. The
object of the invention is to arrange the circuit
15 in such a way that regardless of frequency, volt
age between output terminals will not produce
any voltage between input terminals. This re
sult can be achieved by making the entire net
work symmetrical in the sense that each of the
20 input terminals has a potential which is inter
mediate between the potentials of the output
terminals in the same proportion. While not
the only way to obtain this result, the simplest
way is to duplicate all the impedancesof the
25 tube system (shown in the upper half of the net
work of Fig. 1B) by a similar set of impedances
(shown in the lower half of Fig. 1B) and which
may be called the neutralizing network. In this
way it is obvious that the potentials of the input
30 terminals are each half way between the poten
tials of the output terminals and since the input
terminals have the same potential (in the ab
sence of impressed signal voltages) in spite of
voltage across the output, the object of the in
35 vention is attained.
The inductances serving to simulate the in
ductances associated with the tube are charac
terized by a supplemental index N (thus: LNG,
and LNs), whereas the simulations in regard to
40 capacitance are indicated and designated by
NGK (grid-cathode capacitance), NGA (grid-plate
capacitance), NsG (screen-grid/control-grid ca
pacitance), and NSA (screen-grid/plate capaci
tance). Condenser NKA (cathode-plate capaci
45 tance) and NSK (screen-grid/cathode'rcapaci
tance) may be omitted, under certain circum
stances, provided that inherently low' capaci
ties are involved, and that the’waves are not
unduly or abnormally short.
50
7
Fig. 113 represents merely the same circuit
organization drawn in a different form, with the
tube being imagined to be resolved into its ‘con
stituent elements. The reference numerals‘ are
the same as in Fig. 1A, and the symbols used
55 for the different electrodes of the tube are in
the same form as shown in Fig’. 1A.
'
For the balance and simulation of the capaci
tances‘ and inductances arising inside’ the tube,
the use of an inactive tube similar to the tube to
60 be neutralized is particularly well suited. In
this respect the several neutralizing capacitances
and inductances shown in Figs. IA and 1B may
be considered as corresponding to the inter
65
electrode capacitances and lead inductances of
the inactive tube. According ‘to the prior art,
such tube phantoms‘ have merely been employed
for the purpose of allowing of line (circuit) re
duction in transmitter stages containing more
than one tube by that a working tube was re
70 placed by a phantom corresponding to it. How
ever, according to this invention such a simula
tion is‘utilized for a different purpose and in a
di?erent sense, i. e., with the end in view to se
curing neutralization in an ampli?er valve under
.75 conditions independent of the frequency.
Inasmuch as the simulation of a capacity, under
certain circumstances, is more readily feasible
than that of an inductance, it may if conditions
are appropriate, be feasible to interpose in the
leads of the alternating potential applied to the
different electrodes, condensers, and to render the
resultant impedance (apparent resistance) either
ohmic or capacitive.
Fig. 2 shows an extension of the arrangement
shown in Fig. 1B for a single tube, as applied to H 0
a push-pull arrangement. The reference sym
bols referring to the second tube are character
ized by primes ('). It will be unnecessary to
give further explanations for this circuit dia
15
gram.
It is known that the voltages required for such
compensation or balancing may be derived either
from the grid or from the plate circuit of the
stage'in question. Whereas in the case of Figs.
1A and 1B neutralization was effected from the 20
plate end, Figs. 3A and 3B illustrate a circuit or
ganization in which neutralization, in a way as
known basically from the prior art, is e?ected
from the grid. The input circuit of the stage
contains the inductance LI as well as the con
densers Cl; the output circuit contains the in
ductance L and shunt condenser C; the other
circuit elements are the same‘ as those used in
the preceding ?gures. Fig. 3B shows a modi?ed e
representation of the circuit scheme illustrated
in Fig. 3A in order that the homologous or mir
ror-picture simulation may be made more clearly
understandable.
'
'
What I claim is:,
1. A circuit arrangement comprising a tube
having a cathode, a control'grid, a screen grid
electrode within ‘said tube intended to operate
at unvarying potential but actually ?uctuating
in potential when ‘operated at very high frequen 40
cies due to unavoidable or slight’impedances to
high frequencies in 'the circuit between said
screen grid electrode and cathode, input and
output circuits associated with said tube, and
means for counteracting energy transfer from 45
output to input circuits resulting from said ?uc
tuating potential, said means comprising a pair
of series-connected inductances having their
common terminals connected to the tube cathode,
an inductance connected to the control grid, the 50
opposite end of said last mentioned inductance
being connected to the unconnected terminal of
one of the pair of inductances by means of a
condenser, said opposite end of said inductance
being also connected to the unconnected ter
minal of the other inductance’ of the “pair by
means of a pair of series-connected condensers.
2. A neutralizing‘ circuit'for an electron dis
charge device provided with anode, cathode, con
trol grid and screen grid electrodes, comprising a 60
?rst inductance of a value substantially equal to
the self-inductance of the cathode lead having
one end connected to the cathode, a ?rst capacity
of a value substantially equal to the grid-cath
ode capacity having one end connected to the 65
other end of said ?rst inductance, a second in
ductance of a value substantially equal to the
self-inductance of the screen grid lead having
one end connected to the cathode, a second ca
pacity of a value substantially equal to the screen 70
grid-anode capacity having one end connected
to the other end of 'said second inductance, a
third inductance of a value substantially equal to
the self-inductance of the control grid lead hav
ing one end connected to the control grid and 76.
2,119,315
the other end connected to the other end of the
?rst mentioned capacity, and a third capacity of
a value substantially equal to the control grid
anode capacity connected between the last men
tioned connection and the other end of said sec
ond capacity.
3. The circuit according to the invention de
?ned in the preceding claim wherein a capacity
of a value substantially equal to the screen grid
contrcl grid capacity is connected betweenrthe
non-common terminals of the second and third.
capacities.
4:. A neutralizing circuit of bridge form for an
electron discharge device provided with anode,
15 cathode, control grid and screen grid electrodes,
comprising a condenser in the output circuit of
said device connected between said anode and
cathode, a ?rst inductance of a value substan
tially equal to the self-inductance of the control
20 grid lead, a second inductance of a value substan
tially equal to the self-inductance of the screen
grid lead, a direct connection from one terminal
of said ?rst inductance to said control grid lead,
a direct connection from one terminal of said
3
second inductance to said cathode, the other
terminals of said two inductances being connect
ed together through a condenser whose value is
equal to the value of the internal capacity be
tween said control grid and screen grid electrodes,
two serially connected condensers arranged in
parallel with respect to said last-named con
denser, one of said two serially arranged con
densers having a value substantially equal to the
value of the internal capacity between said anode
and control grid, the other of said two condensers
having a value substantially equal to the inter
nal capacity between said anode and screen grid,
a connection between the junction point of said
two condensers and said output circuit, and an
inductance and a condenser connected in series
between the cathode and said other terminal of
the ?rst inductance, said inductance being of a
value substantially equal to the self-inductance
oi‘ the cathode lead and said condenser being of
a value substantially equal to the value of the
internal capacity between said control grid and
cathode electrodes.
WERNER BUSCHBECK.
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