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Патент USA US2137419

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Nov, 22, 1938.
F.H.SHEPARD.JR
v2,137,419 _
AMPLIFIER CIRCUIT
VFiled. May 28, 1934`
2 Sheets-Sheet 1
FRANCIS H.5HEPARD JR.
BY
)fgQ¿Mm
ÁTTORN Ev
Nov. 22,1938.
‘ ' F. H. sHIEÀPARD. JR
'y
2,137,419
AMPLIFIER CIRCUIT
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0f’ INVENTOR
FRANCIS H. SHEPARD JR.`
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BY
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Patented Nov. 22, 1938
2,137,419
‘UNITED STATES PATENT oFFicE
2,137,419
ADIPLIFIER CIRCUIT
Francis H. Shepard, Jr., Rutherford, N. J., as#
signor to Radio Corporation of America, a cor
poration of Delaware
Application May 28, 1934, Serial No. 727,968
10 Claims. (Cl. 179-471)
The present invention relates generally to am
Figure 7 shows an improved circuit arrange
plifiers and more particularly to so called D. C. ment over the system shown in Figure 6 eliminat-,
ampliñers, of the type adapted to amplify D. C. ing the use of additional voltage sources;
and low frequency A. C.
Figure 8 illustrates a system like that shown
For 'many applications it is desirable to have in Figure '7 except that means are provided for
an amplifier that will efñciently amplify small eliminating the eii‘ects of line voltage variations;
D. C. voltages. In systems heretofore known, and,
Figure 9 is a diagrammatic representation of
where more than one stage of amplification is
needed, D. C. ampliiication is not obtained easily an improved and simplified ampliiier incorporat
10 for the reasons that either there must be sepa
ing the features of the present invention.
rate batteries for each stage, or a set of bucking
Attention is now directed to Figure 5 wherein
batteries for each stage, or a set of divider re
lines 5 and 6 are adapted to‘be connected to a
sistors foreach stage, or again, a very high suitable commercial A. C. power supply network
voltage source across which the various stages .by means of terminals I and 2. A space dis
15 m-ay be placed in series with each other, or a charge device T1 provided with anode, cathode
modulator system where the D. C. is converted and grid electrodes acts as a first amplifier for the
into A. C., amplified and then re-converted back D. C. input. 'I'he input circuit of tube T1 com
into D. C. All of the methods mentioned above prises a connection between the grid electrode
are more or less complicated and furthermore are and the cathode and includes terminals 3 and
quite critical to adjust.` It is also desirable to have 4, across which the D. C. to be amplified may 20
an amplifier oper-ating directly on raw A. C. for
use with a photo tube and other industrial uses
be applied in any desired manner.
as for instance temperature control systems and
burglar alarm systems.
The present invention may be broadly stated
so as to maintain the grid of the tube T1 at
a predetermined operating potential with re
spect to the cathode thereof. The cathode of 25
to comprise a method and means for cascading
grid controlled recti?iers to produce a D. C. am
plifier system which does not necessitate cas
tube T1 is also connected to the line 6, while
the anode of the tube is connected to the line
5 through a resistor R1 which is shunted by
a condenser C1. The anode of tube T1 is also
connected to the line 6 through a resistor l'tz`
and a series condenser C2. A second amplifica
tion stage may be provided and comprises an
electronic tube T2 having an anode, a cathode
and a control grid. 'I'he grid of the tube T2
is connected directly to a point intermediate 35
resistance R2 and condenser C2 and there is
thus provided a. direct connection between the
anode of tube T1 and the grid of tube T2 through
resistor R2. The anode of tube T2 is connected
to the line 5 through a suitable resistor Rs which
is shunted by a condenser Ca while the cathode
of the tube is connected directly to line 6. The
anode of tube T2 is also connected to line 6
by means of a connection including resistor R4
cading the necessary tube energizing voltages.
The invention also contemplates a method and
means for correcting for variations in the sup
ply voltage.
'
Bro-adly speaking, in the present system the
negative voltage developed on the plate of a grid
controlled rectiñer tube connected across an A. C.
line is used to bias the grid of a following tube
also‘connected across the line. The energy to
be amplified is impressed -across the input of
the iìrst tubeA and the amplified energy is avail
able across the output of the last tube.
The various broad aspects of the invention are
illustrated by the circuit diagrams in the ac
companying drawings wherein,
Figures 1-4 represent curve sheets showing
various tube operating characteristics of use in
describing the present invention;
Figure 5 illustrates diagrammatically a circuit
diagram incorporating, in a simple manner, the
broad features of the present invention;
Figure 6 is a diagrammatic representation of
50
a circuit arr-angement differing. from that shown
in Figure 5 only in that means are provided for
increasing the gain of the amplifier by causing
the tubes to be operated at or near the steep
5.5. part of their grid voltage plate current curves;
A bias bat
tery B1 may be provided in the input circuit
and a series condenser C4.
45
A third stage may be similarly connected.
This stage may also include an electronic tube
T3 provided with anode, cathode and grid elec
trodes. The cathode of T3 is shown connected
to the line 6. The anode is connected to the 50
line 5 through a resisto-r R5 shunted by a con
denser C5.
The control grid is connected to
a point intermediate resistor R4 and condenser
C4. It is obvious that any number of succeeding
stages may be added, it being understood that 55
2
2,137,419
causes a'pulsating D. C. current to flow through
only does away with the necessity for a battery
such as B2, (Figure 6) but also acts to partly
counteract the above mentioned instability due
to line voltage variations. For instance, in the
system shown in Figure 7, if the line voltage
falls, the drop across the plate resistor of a tube
will tend to become less with the result that the
grid biases of the various tubes Will tend to de
crease. However, the superimposed D. C. on the
line will also decrease and this will tend to make 10
the plate potentials or grid biases of the various
tubes more negative.
the tube so that the D. C. potential of its plate
or anode becomes negative with respect to the
Thus, the change in rectified superimposed
D. C. due to the line voltage variations can be
three stages have been shown for purposes of
illustration only.
In Figure 5 a utilizing circuit or load shown
generally as a voltmeter V is connected across
the resistor R5.
From the above it can be seen that the cir~
cuit shown in Figure 5 cascades three tubes which
have A. C. on their plates, for the purpose of
amplifying D. C. and/or low frequency A. C.
voltages applied to the input terminals 3 and 4.
In operation, the rectifying action of each tube
15 line.
The grid bias on a tube will determine its
effective plate conductance while conducting,
that is, during the half cycle when the plate
is positive, and hence, will control the amount
of rectified current passed through its respective
plate resistor. The IR drop variations across
the plate resistor are in excess `of the bias vari
ations, hence in accordance Ywith Well known
principles, the tube Will act as an amplifier. As
the D. C. potential across both sides of an A. C.
line is zero, the voltage drop across the plate re
sistor of any tube» may be used after passing
it through a suitable ñlter so as to obtain an
average value, as bias for the next tube. In this
way any number of stages may be used to ob
made to oppose the effects of the A. C. line volt
age variations, if it is so desired. In an actual
circuit built as shown in Figure 7 it was found
that the instability for a given sensitivity can be
reduced to approximately 1/6 of that obtained
in circuits such as those described in Figures 5
and 6.
As pointed out above in connection with the
description of the circuit arrangement shown in
Figure '7 the instability in that system due to line .
voltage variations is only partially counteracted.
It is conceivable that in some systems it would
be highly desirable to have a circuit arrangement
for the purposes described which within certain
in a circuit similar to that shown in Figure 5, a
voltage gain of about Il per stage can be readily
limitations is absolutely independent of line
voltage variations. Such a circuit arrangement 30
has been shown in Figure 8 wherein a potentiom
eter resistance R6 is connected across the lines
5 and 6 and a connection from the anode of tube
realized.
T1 to a point on said resistor Re including a
In a circuit such 'as shown in Figure 5 the gain
of any tube is limited by the factthat the D. C.
variable tap arrangement 'l and condenser C1 is
provided. Condenser C1 in Figure 8 instead of
directly shunting the resistor R1 as in Figure 7
is connected to the supply lines through the po
tentiometer resistor Re. In other respects the
circuit arrangement of Figure 8 is similar to that
shown in Figure 7. By means of the potentiom
eter 1, Re the A. C. voltage on the plate of
tube T1 can be varied independently as regards
30 tain the required'voltage amplification. In prac
tice, it has been found that using type 53 tubes
voltage drop in its respective plate resistor is
limited to the grid bias voltage required for the
next tube. This makes it necessary'to use a very
low value of plate resistor or to operate the tubes
with a very high negative bias in order to make
the grid bias equal the plate load voltage drop.
In either of the above cases a great sacrifice in
eilìciency is made.
The circuit arrangement shown in Figure 6
is concerned with a system for overcoming the
above mentioned loss in efliciency. It is ap
parent at once from a study of the circuit shown
in Figure 6, that the only difference in the sys
, tems shown in Figures 5 and 6 is that in the lat
ter a' battery B2 is placed in series with the A. C.
line so that the drop in the plate resistor might be
increased to a value equal to the battery voltage
plus the grid bias voltage.
This arrangement
makes it possible to operate the tubes more ef
iiciently and, in fact, it was found in an actual
set up using type 53 tubes that a voltage gain of
between 25 and 35 per stage may be easily at
tained.
l
the D. C. voltage: In this way the A. C. and D. C.
effects described above in connection with Figure 45
7 can be made to perfectly compensate for each
other and make the amplification and level of
output current independent of line voltage va-riations Within said limits. The theory under
lying the above can best be illustrated by the q
following:
A triode may be operated with A. C. on its
plate to amplify changes in the D. C. bias applied
to its grid. ’The tube will act as a rectifier and
will build up a negative voltage on its plate.
The value of this voltage can be controlled by the '
grid potential of the tube. When pure D. C. is
applied to the plate of a vacuum tube through
a load resistor the assumed D. C. potential of the
It is quite obvious from a consideration of the
system disclosed in Figure 6 that the use of a
separate source such as battery B2 is inconveni
ent and should be avoided.v For this purpose,
the system shown in Figure 7 will now be con
sidered. In Figure '7 the battery B2 of Figure 6
65
has been displaced by the diode rectifier D1 con
nected across the line 5, E and a condenser Ce,
interposed between terminal l and the connec
tion between the cathode of D1 and line 5. In
plate is always positive and varies with the supply
7o; connection with the systems shown in Figures 5
bias variations. If the AC/DC ratio is too high 70
over-compensation will result and if it is too
low there is obtained under-compensation. Be
cause of the fact that a single stage of the ampli
lier may be considerably over-compensated all
60
and 6 it was also found that when amplifying
very small voltages through a number of stages,
linevoltage variations which are also amplified
make the ampliñers unstable. The use of a recti
ñer or diode ‘D1 such as shown in Figure '7 not
voltage. By placing both A. C. and D. C. on the
plate of the tube simultaneously and keeping the
ratio of A. C. to D. C. constant as is the case
where the A. C. is rectified to supply the D. C.
the two effects can be made to oppose each other 65
for the effects of line voltage variations. If the
proper AC/DC ratio is chosen there can be ob
tained practically perfect compensation over cer
tain ranges of line voltage variations and grid
the compensation for several stages in cascade 75
2,137,419
may be obtained in one of the stages only, hence,
as shown in Figure 8 the compensating effect is ob
tained only in the ñrst stage and may be of such
a‘value as to compensate for all the succeeding
stages of the amplifier.
`While no mention has been made of the ef
fects of heater current variations which cause
effective changes in the temperature of and hence
'in the contact potential- between cathode and
grid and changes in the velocity of emission of
electrons from the cathode, which changes are
equivalent to `actual changes in grid bias, it is.
apparent that the AC/DC ratio may be adjusted
so that this heater effect can also be compensated
for. However, the compensation in the case
previously discussed will take place immediately
with line voltage variations while the effects due
to cathode temperature will lag behind the volt
age changes. If the time constant of the -re
20 sponse of the amplifier is greater than the heat
ing time of the cathode, compensation can be ac
complished `without any instantaneous de
compensation.
For a clearer understanding of the operation
25 of the system herein disclosed attenti-Onis now
directed to Figures 1 through 4.
connected to an A. C. power supply system
through terminals I and 2. For purposes of il
lustration only three tubes T5, T5 and T7 have 25
been shown comprising the amplifier, however, it
is to be distinctly understood that any desired
cation curves for a triode with various values of
A. C. on the plate and with Zero bias on the grid.
number of tubes may be’utilized and connected
grid, the plate voltage current curve of a triode
is shifted parallel to itself along the voltage axis,
see Fig. 3. This causes the whole family of rec
35 tification curves to shift along the voltage axis.
Figure 2 shows how the rectification curves
have shifted from the position shown in Figure 1
when thegrid biasis` changed from zero to a
negative value. A load line A--B placed in Fig
as taught by the present disclosure. The ñrst
tube T5 includes anode, cathode and grid elec 30
trodes. One side of the cathode is connected to
line Ei while the anode is connected to conductor
5 through condenser C8. The anode is also con
nected to conductor- t through two paths one of
which includes the resistor Rin and the other a 35
resistor R11 and a condenser Cè in series. The
D. C. input is applied across terminals 3‘ and 4,
terminal 3 being connected to the grid of T5 while
ures 1 and 2 will intersect the constant A. C.
lines at different points on the two sets of curves.
terminal 4 is connected to a point on the resistor
R10 by means of a variable tap I2. A condenser
C7 is connected between the connection from
For instance, the load line in Figure 2 intersects
terminal ll to the resistor R111 and conductor 6. .
the siX volt A. C. line at a plate potential of Zero
The second tube is also shown as including
anode, cathode and grid electrodes, the anode
being connected to the conductor 5 through a
volts.`- . With a less negative bias, as shown in
Figure 1, the plate voltage will be some value less
than Zero. In this way the grid bias can be used
to control the potential on the plate and since
this plate potential can be normally around zero
it can be coupled (through a simple filter to re
50 move the A. C.) directly to the grid of a follow
ing amplifier stage (see, for instance, Figure 8
where the anode of tube T1 is coupled directly
to the grid of tube T2 through the resistor R2)
the condenser C2 acting as a ñlter element.
Referring again to Figures 1 and 2, if the
D. C. supply potential is increased the plate po~
tential will increase.
If the A. C. is increased
the plate potential will decrease. If both the
A.` C. and D. C. supplies are increased together
60 inthe proper ratio there will be no change in the
D. Cjplate potential.
In the circuit arrange
ment shown in Figure 8 a rectifier is used to pro
videthe D. C. supply, while the A. C. is supplied
from the potentiometer arrangement 1, R5 con
65 nected across the line through a low impedance
condenser C1 to the plate of the tube. The proper
ratio between the A. C. and D. C. for perfect
compensation may be obtained by adjusting the
value of the A. C. by means of variable tap 'I.
As stated previously, it is possible to over-com
pensate or under-compensate the circuit so that
the plate potential may vary in either direction
with varying line voltage. Because of this fact
it is possible to compensate in one stage the
75 effects of line voltage variations in the other
70
ode temperature will have an effect, due to the
velocity of emission of the electrons and contact
potential on the cathode, equivalent to a change
in grid bias.
10
Figure 4 shows a characteristic curve for bias
which is equivalent to cathode exciter voltage
changes. Since there is a definite relation be
tween ñlament voltage and equivalent grid bias
it is possible to compensate for filament voltage
variations within limits in the plate circuit by
the method outlined above.
Attention is now directed to Figure 9 which
shows in diagrammatic form a simpliñed A. C.
operated D. C. amplifier circuit that is self biased
and compensated for line voltage variations. As
in Figures 5 through 8 conductors 5 and 6 are
In Figure 1 there is shown a family of rectifi
30 This‘set of curves is similar to the curves usually
shown for a diode detector. By means of the
55
3
stages and it is also possible to compensate for
the eiîects of heater voltage variations, as will`
be more fully covered below. As long as the
plate current is small compared to the emission
current of the cathode, that is, under unsaturated
cathode current conditions, changes in the cath
condenser C10 while one side of the cathode is
connected directly to the conductor 6. The sig
nal grid of the tube T5 is connected to a point
on the resistor R11 by means of a variable tap I3.
As in the case of tube T5 the anode of tube T5
is connected to the conductor E through two
paths. One of these paths includes a resistor
R12 while the other comprises resistor R13 and
a condenser C11 in series. The third tube of the
system T7 i-s also provided with anode, cathode
and grid electrodes, the cathode being connected
directly to the conductor E while the grid elec
trode is connected to a point intermediate re
sistor I3 and condenser C11. The anode of tube
T1 is connected to an output terminal l I, ter 60
minal I0' shown at one end of the conductor 5
being the other output terminal of the system.
It is to be understood that any desired utilizing
system may be connected across the output ter
Ininals` I0 and II.
65
For a proper understanding of the operation
of the system shown in Figure 9, attention is di
rected again to the curve sheets shown in Fig»
ures 1 and 2. It will be noted that the load line
OC starts from Zero as there is no D. C. supply 70
in the circuit shown in Figure 9. 'I'he plate volt
age will always be negative as shown by the in
tersections with the triode rectification curves.
The actual value of D. C. plate voltage with a
constant A. C. voltage on the plate will vary with
4
2,137,419
tential due to the rectifying action of the tube.
This potential, for best amplification, will be too
to that given above in connection with the de
scription of curve sheet shown in Figure 4.
In the system shown in Figure 9 the slider I3
should be adjusted along the resistor R11 so
that the grid of the tube Ts swings into the op
erating range of the tube but never swings posi
tive with'respect to the cathode.
high a Value to use directly for self-bias. How
ever, since ’the load resistor is returned to ground
or zero potential, a slider may be placed on this
of none of the resistances and condensers used
are critical. In one of a number of practical
the grid bias.
This is shown by observing the
intersections of the constant A. C. lines with the
D. C. load line in Figures 1 and 2. In normal
operation, considering the tube T5, the anode
will assume a highly negative average D. C. po
resistor to obtain any average D. C. Voltage from
zero to the average D. C. potential of the plate.
It is possible in some particular instance that the
D. .C. potential may be in the order of -80 volts.
If -4 volts isV the normal bias for the tube
in this circuit, the slider is adjusted along the
load resistor R10 (see Figure 9) until a potential
of -4 volts is reached. Condenser C1 is üsed as
a filter to by-pass the A. C. on the top portion
'lil of the divider resistor R10. This will keep the
A. C. oiî the grid of the tube T5. If the normal
a 2000 ohms resistor was used for the A. C. line
shunt while the plate resistances were each one
megohm, the grid resistors two megohms and
the condensers 0.1 mmf.
While the invention has been described by cer
tain particular embodiments, it is to be under
stood that the principles underlying the inven
tion may be carried out in many other forms f
without departing from the spirit of the inven
tion, and no limitations upon the invention are
-80 volts, the slider will be set approximately
V20 of the way up the load resistor R10 and the
degeneration due to the self-bias will be one part
in 20, times the actual realized voltage gain. It
should be understood, of course, that the values
given above are approximate values that can be
intended other than those imposed by the scope
of the appended claims.
I claim:
1. In an alternating current operated direct
current amplifier, an electronic tube including
The potentiometer R11 as far as D. C. is con
cerned is merely a resistor of negligible Value
in series with the grid of tube Ts. Condensers
C10 and C11 have no eiïect on the D. C. voltage,
however, potentiometer R11 as far as A. C. is
36 concerned will act as a voltage divider resistor
across the line. Condensers Ca and Cs have neg
ligible impedance to A. C. The instantaneous
potential on the grid of tube Te is the sum of
the D. C. voltage on the plate of tube T5 and the
40 instantaneous value of A. C. at the point to which
the slider I3 is set on the resistor R11. During
the part of the cycle that the tube Te is conduct
ing. the instantaneous A. C. voltage applied to
the grid of tube Te is in such a direction as to
oppose the normal D. C.,bias supplied by the plate
45 of
the vacuum tube T5. Thus, the grid during
the conducting part of the cycle will be less nega
tive than the normal bias and will be of such
a value that the grid of the tube Ts will be at a
50
embodiments of the invention, and in particular
one that followed the diagram shown in Fig. 8,
bias is ' -4 volts, when the plate potential is
expectedV in normal operation of the system.
30
In practice it has been found that the values
suitable operating potential.
» Suppose that the A. C. line voltage, that is,
the A. C. voltage on the anode is increased it
can be seen from the rectification curves in Fig
ures 1 and 2 that the negative plate potential
This will cause the normal grid
bias of tube Ts to become more negative. How
ever, increasing the A. C. line Voltage would
also cause an increase in the superimposed A. C.
on the grid on the tube T6 and this will tend
60 to make the grid more positive during the op
erating part of the cycle. Since the two above
mentioned effects can be made to oppose each
other the eñîects of line voltage variations may
55 will increase.>
be nulliñed. Compensation adjustment is made
an anode, a cathode and a grid electrode, a source
of alternating current energy including a pair
of line conductors, a connection including a re 30
sistor element between one of said conductors
and the anode of said tube, a connection between
the cathode and the other line conductor, an in
put circuit for said tube including said grid elec- ~
trode and the cathode, a capacitive impedance
shunted across said resistor element and a filter
circuit comprising an impedance device and a
condenser connected between the anode of said
tube and the cathode.
2. In a direct current amplifier, a pair of con 40
ductors adapted to be connected to a source of
alternating current, a controllable rectifier corn
prising an electronic tube having anode, cathode
and control electrodes, a connection including a
high plate resistor between the anode and one 45
of said conductors, a connection between the
cathode and the other conductor, an input cir
cuit for said tube including the cathode and
control electrode thereof and means adapted to
connect the input circuit to a source of energy 50
to be amplified, a second controllable rectifier
comprising an electronic tube having anode, cath
ode and grid electrodes, a connection between
the anode of the last named tube and one of
said conductors including a plate resistor, a con
nection between the cathode of the last named
tube and the other conductor, a direct connec
tion between the anode of the iirst tube and the
control electrode of the second tube including
an impedance device, whereby a controlling volt 60
age is impressed upon the control electrode of
the second device as determined by the drop
across the high plate resistor associated with the
first tube due to the flow of current therethrough,
65 by varying the A. C. voltage on the grid of tube
said controlling voltage being normally too nega
Ta by adjusting the slider I3 on the potentiom
eter R11. As previously stated, it is possible to
obtain overcompensation, hence, it is possible to
perform all the necessary compensation for sev
70
eral stages in the one stage. It is also possible
as previously pointed out to accomplish compen
sation for the effects of filament voltage varia
tions. The explanation for filament compensa
tion in the circuit shown in Figure 9 is similar
tive as regards the normal operating character
istics of the second tube to produce proper op
eration thereof and mea'ns for impressing a po
tential upon the anode of the ñrst tube with re
spect to the cathode thereof of such direction 70
and amplitude to partially compensate for the
high drop across the plate resistor of the first
tube whereby there is impressed upon the control
electrode of the second tube a control voltage 75
2,137,419
commensurate with the proper operation of said
tube.
-
`1
,
‘
`
~
3. In a direct current amplifier, a pair of con
ductors adapted‘to be conneotedto a sourceof
alternating current, a controllable rectifier com
prising an electronic tube having anode, cathode
and control electrodes, a connection including a
between the alternating current and direct cur
rent voltage applied to the plate of the tube is
maintained constant by deriving the direct cur
rent voltagefrom the alternating current voltage
whereby variations in voltage of one causes `like ,
voltage variations of the other. .
„ 8. In `anv alternatingcurrent operated direct
high plate resistorbetween the anode and one of
currentv` amplifier, . a source» of l alternating cur
said conductors, a connection between the cath
rent, a plurality of cascaded electronic rectifiers
connected across the source in parallel, each of
said rectifiers including a control element ar
ranged so as to control the rectifying action of
the rectifier, a source of energy to be amplified,
lO ode and the other conductor, an input circuit for
said tube including the cathode and control elec
trode‘thereof and means adapted to connect the
input circuit to a source of energy to be ampliñed,
a second controllable rectifier comprising an elec
tronic tube having anode, cathode and grid elec
trodes, a connection between the anode of the
last named tube and one of said conductors in
cluding a plate resistor, a connection between the
cathode of the last named tube and the other con
ductor, a direct connection between the anode
of the first tube and the control electrode of the
second tube whereby a controlling voltage is
impressed upon the control electrode of the second
device determined by the drop across the high
25 plate resistor associated with the first tube due
to the flow of rectiñed current therethrough, said
controlling voltage being normally too negative
as regards the normal operating characteristics
of the second tube to produce proper operation
30 thereof and means for impressing a potential
across said two conductors of such direction and
amplitude as to partially compensate for the high
drop across the plate resistor of the first tube
whereby there is impressed upon the control elec
35 trode of the second tube a control voltage com
means for connecting said last named source to
the input of the first of said cascaded reotifi-ers 15
to control its action in accordance with energy
to be amplified, means for controlling the recti
iying action of each of the other rectifiers in
accordance with the rectiñcation of energy by the
respective preceding rectifier, means for impress 20
ing a unidirectional potential across the space
path of at least the first rectifier, the direction
and amplitud-e of said potential acting to par
tially compensate for the potential applied to the
next successive tube.
25
9. In a direct current amplifier, a source of
alternating current including a pair of terminals,
a first conductor connected to one of said ter
minals and a second conductor connected to the
other of said terminals, a diode rectifier element 30
including an anode and a cathode, the cathode
the positive potential side of the rectifier is con
of said rectifier element being connected to said
first conductor and the anode thereof being con
nected to the other of said conductors, an elec'
tronic tube provided with an anode, a cathode 35
and a control electrode, means including a plate
resistor for connecting the anode to the ñrst
named conductor, means for connecting the cath
ode to the other of said conductors, an input
circuit for said electronic tube including the 40
cathode and control electrode thereof, a connec
tion between the anode of said electronic tube
and the cathode thereof including a resistor and
nected to that conductor which is connected to
a capacity connected in the order named, a ca
mensurate with the proper operation of said
second tube.
4. The system described in the next preceding
claim further characterized by that the means
40 for impressing the potential across the two con
ductors comprises a rectifier device connected
across the two conductors and arranged so that
pacity element shunted across said plate resistor, 45
45 the anode of the first tube.
5. The system described in claim 3 further
characterized by that the means for impressing
the potential across the two conductors comprises
a rectifier device connected across the two con
50 ductors and arranged so that the positive po
tential side of the rectifier is connected to that
conductor which is connected to the anode of
the ñrst tube and wherein the rectiñer device is
adapted to be connected to a source of alter
55 nating current through a condenser said system
being further characterized by that the compen
sating voltage also acts to partly counteract in»
stability of the amplifying system due to line
voltage variations.
6. A method of amplifying a direct current
voltage applied to a control grid of an electronic
tube which comprises impressing both an alter
nating current voltage and a direct current Volt
age upon the anode of the tube so that the tube
65 will act as a rectifier and thereby build up a
60
negative voltage on its plate, controlling the
value of this negative voltage by the grid po
tential applied to the control grid and main
taining the ratio of the alternating current volt
70 age to the direct current voltage applied to the
plate constant and of such a value that effects
of alternating current line voltage variations are
i compensated.
Y
7. The method described in the next preceding
75 claim further characterized by that the ratio
a second electronic tube including an anode cath
ode and control electrode, a connection between
the control electrode and the cathode thereof in
cluding said first named capacity element and
means includinga plate resistor for connecting 50
the anode of said second named electronic tube
to the ñrst named conductor, a utilizing circuit
and means for connecting the utilizing circuit
across said last-named plate resistor.
10. In an amplifier circuit including at least 55
two cascaded electron discharge devices each of
said devices including anode, cathode and grid
electrodes, a source of alternating current pro
vided with a pair of terminals, a line conductor
connected to one of said terminals and a line 60
conductor connected to the other of said ter
minals, a resistor device connected between saidV
two conductors, a diode rectifier having its cath
ode connected to the first of said conductors and
its anode connected to the second, a connection 65
between the anode of the first of said two electron
discharge devices and the first of said conductors
including a load resistance, a connection between
the last named anode and a point of said first
named resistor including a condenser, a connec 70
tion between the other line conductor and the
cathode of said first electron discharge device,
an input circuit for said first electron discharge
device including the grid and cathode thereof, a
connection between the anode ofthe second of 75
6
2,137,419
said electron discharge devices. and the iirst line
conductor including a. load resistor shunted by a
condenser, a connection between the anode of
said second electron discharge device and the
cathode thereof' including an impedance element,V
means for connecting the cathode of the second
electron discharge device and the cathode of the
ñrst electron dischargei device, a connection be
tween the anode of the first electron discharge
device and the cathode thereof including a re
sistor and a condenser in series and a connection
between the grid electrode of thev second named
electron discharge device and a point of said last
named circuit between the resistor and con
denser.
'
FRANCIS H. SHEPARD, JR.
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