Download Amplifier

Sept. 1, 1937.
2092,49@
H. BRANSON
AMPLIFIER
- Filed Nov. 26,
1932
.
T.I
H/.S Á T MEA/E .
v2,092,496
"Patented Sept. 7, 1937
" UNITED -STATES PATENT OFFICE
Harry Branson, Philadelphia, Pa., assignor to
-
Radio Corporation of America, a corporation
of Delaware
> _
Application November 26, 1932, Serial No. 644,41*!V
'l Claims.
My invention relates to ampliiiers and, more
particularly, to amplifiers intended for inter
mittent periodic operation.
(ci. 17a-70)"
i
In connection with recent developments in
5 television, the need has arisen for an amplifier
that may be rendered substantially instantane
ously operative or inoperative without causing
the appearance of disturbing impulses in the out
put circuit thereof.' Such an amplifier is espe
10 cially adapted for use in transmitting television
pictures and accompanying sounds over a single
radio channel and is also useful for the purpose
of introducing synchronizing signals in the same
' channel as that which carries the picture im
15
pulses.
y
'
Furthermore, an` amplifier of the type de
scribed may be used to reduce the signal from
any source to zero at definite periods, such as
for use in connection with cathode ray television
ltransmitting tubes, and it may also be utilized
The foregoing objects and others appurtenant`
thereto I prefer to accomplish in brief as follows:
I provide in my improved amplifier a plurality
of main amplifying tubes connected in cascade
and having a final output circuit across which
appear the amplified signals. In addition. I pro
vide what will hereinafter be termed a control
tube which is utilized to substantially instan
taneously control the gain in the Vfirst of the
main amplifier tubes in response to a control 10
signal. I also provide an auxiliary thermionie
tube, the output circuit of which is differentially
included in or coupled to the final output cir
_ cuit of the system and so interconnect the con
trol tube with the intermediate tube that the 15
latter serves to introduce into the ñnal output
circuit impulses that neutralize whatever tran
sient potentials may appear therein >when the
gain in the first amplifier tube is abruptly
changed.
i
20
The novel features that I consider charac
tem where the signals must exist at separated teristic of my invention are set forth with par
times insofar as the entire system is concerned. ticularity in the appended claims. The inven
Ampliñers heretofore constructed for " the, tion itself, however, both as to its organization
aforementioned purposes have been open to the and advantages thereof, will best be understood
serious objection that, wheneve'ì‘ their condition from the following description of a specific 4em
is changed from inoperativeness to operativeness, bodiment when read in connection with the ac
for introducing more than one signal into a sys
and vice versa, at rapidly recurring intervals,
very objectionable harmonic impulses and im
companying drawing, the single figure of which
is a diagrammatic View of an amplifier includ
pulses occasioned by‘ abrupt variations in the _A ing a preferred embodiment of my invention.
plate supply to the amplifier tubes appear in the
output.l Obviously, these disturbing impulses
>mar the effect of a received picture whether they
- appear at the transmitting -or at the receiving
v35
end of the system, and militate against the use
fulness of the amplifier when employed for any
of the aforementioned purposes.
It is, accordingly, an object of my invention
to provide an amplifier the condition of which
40 may be substantially instantaneously ~altered
from inoperativeness to operativeness, and vice
versa, without causing the appearance of objec
tionable impulses in the output circuit thereof.
A further object of my invention is to provide
45 an amplifier the gain in which may be instan
taneously altered from zero to maximum, and
vice versa, without the introduction of a “hang
over” effect, which would interfere with the
` proper amplification of incomingor outgoing sig
a
.
A still further object of my invention is to
provide an ampliñer such that it may be utilized
for introducing more than one signal into a
transmitting or receiving system, whether radio
55 or carrier current.
Referring specifically to the drawing, my iin
proved amplifier includes an amplifying ther
mionic tube I preferablyy of the screen grid typev
having an input or control grid 3, a cathode 5,
a screen grid 1, 'and an anode 9. The anode 35
output circuit includes a resistor Il which- is
connected to the cathode 5 through a source I3
of high potential and a resistor I5.
'I‘he tube I is provided with a grid resistor I1
and it is normally biased to the cut-off potential 40
by a source I9, the positive. terminal of which
is connected to the junction between the nega
tive terminal of the high potential source and
the resistor I5. The output resistor II is coupled
to a second amplifier tube 2i, which may be of 45
any desired type, through a stopping condenser
23 and a connection 25 common to the cathodes
of the several tubes.
The output circuit of the second amplifier tube
2l includes a resistor 21 through which plate 50
potential is supplied to the tube from the high
potential source.
' The first amplifier tube I, as above mentioned,
is normally maintained in the inoperative con- -
`dition by‘reason of high negative potential ap
2
2,092,496
plied to the grid thereof from the source I9. In
this condition, the gain, of course, is zero, and
any_.-signal which is applied to the input termi
nals thereof is not amplified.
In order that the gain in the tube I may be
Ul
shifted from zero to an operative value, I provide
a control tube 29 having an anode 3| which is
connected to the cathode terminal of the resistor
I5, and a cathode 33 which is connected to the
10 grounded terminal of the same resistor through
a potential source 34. 'I'he control tube is pro
vided with a grid resistor 35 and with a source
of grid bias potential 31, the voltage of which is
adjusted to either bias the tube to the cut-off
15 point, or to the point at which it operates best,
depending upon the shape of the control impulse.
For example, if a source 38 of square top waves
is available for control purposes, the control
tube 29 is merely biased to the point where it
20 functions as a linear amplifier.
If, on the other
hand, only a source of sine-wave potential is
available for control purposes, the control tube
is biased to the cut-01T point, which permits only
the peaks of the positive half-cycles to be ef
25
fective.
u
_
Irrespective of the manner in which the con
trol tube 29 operates, however, a positive pulse
applied to the grid thereof permits space cur
30
rent to flow therein, which current, in flowing
through the resistor I5, develops a potential that
opposes the potential applied to the grid of the
tube I from the bias potential source I9. Ac
cordingly, as soon as the tube 29 is made con
ductive by a control impulse, the amplifier tube
r I abruptly becomes operative and the amplified
incoming signal is impressed upon the grid of
the amplifier tube 2| and appears across the
output resistor 21 thereof.
By reason of the abrupt change in plate cur
rent flow in the first amplifier tube I, undesir
able impulses appear across the output resistor
I I thereof. For the purpose of minimizing the
effect of such impulses, I provide a neutralizing
tube 39, also preferably of the screen grid- type
45 having a cathode 4|, a control grid 43, a screen
grid 45, and an anode 41. The cathod’e is di
rectly connected to tlie cathode of the first am
pliñer tube and the control grid is connected to
the low potential` end of the grid resistor I1 of
50 the said tube. The anode of th'e neutralizing
tube is connecte/d to the anode of the amplifier
tube 2|, the connection including a resistor 49
abrupt and the surge of plate current in the
tube I which flows at the instant the tube 29
“unlocks", so to speak, the said amplifier tube
causes transient, undesirable potentials to appear
across the output resistor II and, ultimately,
across the resistor 21.
At the same time, how
ever, the auxiliary tube 39 is rendered operative
and its plate current abruptly rises to cause the
same transient potentials to be developed across
the output resistor 49 connected to the plate
thereof. It will be noted, however, that the po
tentials developed across the resistor 49 by rea
son of abrupt changes in the conductivity of the
tube 39 are 180° out of phase with the analogous
potentials developed across the -resistor 21.
In
sofar as the output circuit of the system is con
cerned, which serially includes the resistors 21
and 49, the transient impulses are can'celled, and
do not appear.
From a consideration of the` foregoing, it
might be inferred that, if transient impulses are
neutralized, the input signals ,would also be neu
tralized during periods of activity of the ampli
ñer tube I. This is not the case, however, since
only a fractional part of the amplified signal po
tential appears across the resistor I5 and such
potential, by reason of the circuit connections,
when applied to the neutralizing tube, is in
proper direction to offset the degeneration
caused in tube I by the presence of the said re-" 30
sistor.
In describing the operation of my improved
system, it has been assumed that the several re
sistors |I, 21, and 49 have been properly correlat
ed to the gain in the tubes I, 2|, and 39. If the
gain in the tube 2| is unity, the resistors 21 and
49 may have approximately the same magnitude.
It is, however. difficult to provide a tube wherein
the gain is unity and, for best operation, IA have
determined that the output resistor || should be 40
equal in value to the sum of the resistance of the
resistor 49 and the combination` of the resistance
of resistor 21 with the plate impedance of the
tube 2|.
,
In an actual amplifier which I have construct 45
ed according to my invention, the tubes | and 39
are of the screen grid type known as Radiotron
57, and the tube 2| is of the type commercially
known as Radiotron 1'7l-A. The resistor II
has a value of 2,000 ohms, the resistor 49 1,500 50
ohms, and the resistor 21 1,000 ohms. Further
more, the resistor |5 in the cathode circuit of
thágugh which plate potential is supplied to the the
tube | has a magnitude of 7,50 ohms, while
tu
.
'
The screen grid 45 may be connected to the
_ screen grid of the amplifier tube and be supplied
with potential over a common conductor 5| lead
ing to the highfpotential source I3.
To understand the operation of the entire
60
system including the neutralizing tube, let it be
assumed that a signal, representative of picture
frequencies or the like, is being impressed across
the input terminals of the first amplifier tube I,
which normally has zero gain.
At the same time, let it be assumed that a con
trol impulse is being applied periodically to the
input terminals of the control tube, such signal
being either square top from any desired source,
or sine wave as hereinbefore described. Between
70 impulses applied to they control tube, the ampli
fier tube I is inoperative and it is rendered oper
ative to amplify the signals impressed thereon
only during intervals of operativeness of the con
trol tube.
75
4
The action of the control tube, however, is
the plate supply for the system provides a poten
tial of 250 volts. The tube 29 is, preferably, of
the type known as Radiotron 56, which requires
55
a cut-off potential of 30 volts.
An amplifier including a preferred embodiment
of> my invention is normally inactive and is ren
dered operative only when the control tube is en
60
ergized. It will, however, be obvious that such
condition may be reversed, the amplifier being
normally operative and being rendered inopera
tive in accordance with impulses applied to the
input circuit of the control tube. One Way of ob 65
taining the last-mentioned condition is to adjust
the bias battery I9 to deliver a less negative poten
tial, whereupon theblas on the tube I is the alge
braic sum of the potential supplied therefrom, the
drop across the resistor I5, by reason of space cur
rent in the said tube, and the drop across the same
resistor in the opposite direction occasioned by
the flow of space current in the tube 29, which
is so biased as to permit a small amount of cur
rent to flow therein. 'I'he control signal must, 75
3
2,092,498
under these conditions, be negative in order that
the space current in the control tube may be re
:1
duced orstopped, whereupon the grid of the tube I
is immediately biased negatively to the cut-off
point. Another'way of obtaining‘the same con
dition is to omit the bias-battery I9 and to reverse
the connections of the anode 3| of the control tube
and the source 34 to the resistor I5. 'I'he control
tube then functions as first‘described, namely, be
if) comes conductive inresponse to the control im
pulse and develops-a potential across the resistor
in the direction to bias` the amplifier I to the cut
an output circuit, means for abruptly altering
the gain in said tube, an amplifier coupled to said
output circuit, said amplifier havingian output
circuit in which may appear impulses occasioned
by abrupt changes in the gain in the first referred
to tube, and means, energized solely in response
to abrupt changes in gain in said thermionic tube,
for neutralizing impulses in the output circuit of
the amplifier.
5. In combination, a plurality of thermionic 10
tubes each having an input circuit and an output
circuit, connections between the input circuit of
one of said tubes and the output circuit of an
offAlthough
potential.I have chosen a specific
«'- '
embodiment . other of said tubes, connections between the in
of my invention for purposes of illustration, many
modifications thereof will be »apparent to those
skilled in the art to which it pertains. My in
vention, therefore, is not to be limited except inso
far as is necessitated by the prior art and by the
spirit of the appended claims.
I claim as my invention:
w
ì
1. In combination, means for producing control
impulses, a plurality of thermionic tubes con
nected invcascade, means for altering abruptly the
gain in at least one of said tubes in response to the
occurrence of said impulses, and means for com- ‘
put circuit of a third tube and-the input circuit
of the second mentioned tube, and connections
whereby the output circuits of the first and last
-mentioned tubes arel differentially coupled to a
common output circuit, whereby abrupt ‘changes
in potential applied to the input circuit of the
l>second mentioned tube give rise to mutually op
posing effects in the said common output circuit.
6. In combination, a pair of electric discharge
tubes each having an input circuit and an output
circuit, a source of control voltage, said'input
circuits being connected in parallel with respect
. pensating disturbing impulses occasioned by said _ to said source, a source of signal voltage connectedabrupt alterations in gain.
f
across only one of said input circuits, a signal out
2. In combination, means for producing con
trol impulses, a thermionic tube having an input
put circuit, means for coupling one of said tube
circuit and an output circuit, means »for con
means for coupling the other of said 'tube outputï
circuits to said signal output circuit in reversed
phase relation rwith respect to the coupling be
tween said one output circuit and said signal
circuit.
7. In combination, a pair of electric discharge
trolling the gain in said tube in response to the
occurrence of said impulses, and means for
neutralizing disturbing impulses appearing in the
output circuit thereof by reason of abrupt altera
output circuits to said signal output circ?it, and 30
tions' of gain therein.
3. In combination, means for producing control ' tubes each having an input circuit and an output
impulses, an electric discharge tubev having an in- - circuit, an impedance unit common to said two
Í,put circuit and an output circuit, means for
input circuits, means for impressing a control
voltage across said impedance unit, a second im 40
put circuit, means for abruptly altering the gain pedance unit included in one of said input circuits
of said'tube in response to the occurrence of said » only, means for impressing a signal voltage across
control impulses, and means for balancing out said second impedance unit, a balancing circuit, impulses appearing in said output circuit resulting means for connecting one of said tube output cir
45 from said abrupt alterations in the gain in said cuits to said balancing circuit in one phase rela
tion, and means for connecting the other of said
tube.
4. In an amplifier, a thermionic tube having an tube output circuits to said balancing circuit in
40 amplifyingwanted signals appearing in said out
input circuit, across which potential changes
representative of signals may be impressed, and
i
the opposite phase relation.
HARRY BRANSON.