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Патент USA US2134747

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Nov., Í, Í938„
ì 's BALLANT-[NE
2,134,747
VACUUM TUBE AMPLIFIER
IN VEN TOR.’
BY
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m;
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ATTORNEYS.
Nov. l, 1938.
S. BALLANTINE
2,134,747
VACUUM TUBE AMPLIFIER
Filed March :51. 1900
A50
5 Sheets-Sheet. 2
Z50
lIN VEN TOR.'
We W@
Nov. l, 1938.
2,134,747
s. BALLANTINE
VACUUM TUBE AMPLIFIER
Filed March 51. 1930
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IN VEN TOR.’
@fila/«z
MM,
BY
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9%,
A TTORNEYS.
Patented Nov. 1, 1938
2,134,747
UNITED STATES PATENT OFFICE
2,134,747
VACUUM TUBE AMPLIFIER
stuart Ballantine, Moúntain Lakes, N. J., as
signor, by mesne assignments, to Radio Corpo
ration of America, New York, N. Y., a corpora
tion of Delaware
Application March 31, 1930, Serial No. 440,514
21 Claims. (Cl. 250-20)
'I'his invention relates to vacuum tube ampli
ñers and particularly to radio receivers employ
ing radio frequency ampliiiers.
An object of the invention is to provide a vac
CII uum tube amplifier including an improved sys
tem for controlling the output level. A further
object is to provide a vacuum tube amplifier in
cluding volume control apparatus effective to
prevent distortion at high signal inputs and to
preserve a maximum signal to noise ratio. More
specifically, an object is to provide a vacuum tube
amplifier in which the control of volume is ef
iected by changing simultaneously the amplili
cation of the vacuum tube amplifier and the
magnitude of the signal voltage impressed upon
the amplifier.
The novel features which I believe to be char
acteristic of my invention are set forth in par
ticularity in the appended claims, the invention
20 itself, however, as to both its organization and
method of operation will best be understood by
reference to the following description taken in
`connection with the drawings in which I have in
dicated diagrammatically one circuit organiza
tion whereby my invention may be carried into
effect.
i,
These and other objects will be apparentY from
the following specification when taken with the
accompanyingy drawings in which:
Figs. 1 and 2 are curve sheets showing the va
riation of shot-noise with amplification, and
Fig. 3 is a circuit diagram of a radio receiver
embodying the invention.
In conventional radio receivers, the control of
volume or output level has been effected in one
of two ways, i. e., the input voltage has been con
trolled by >a voltage divider which was adjusted
to impress any desired portion of the antenna
voltage upon the first amplifier tube, or the full
Aantenna voltage has been impressed upon the
amplifier andthe radio frequency amplification
has been controlled by regulating the direct cur
rent potential applied to a tube element, for eX
ample, to the control grid. Both of these
methods possess certain disadvantages.
In the ñrst vacuum tube in the radio fre'
quency amplifier there are natural statistical
fluctuations in the electron How between cathode
and plate which, as pointed out by W. Schottky
(Annalen der Physik, vol.
characteristic oscillations
associated with the tube.
cillations are ordinarily of
5_7, 541, 1918), cause
in the tunedv circuits
In practice these os
such small amplitude
as to be inaudible in the absence of an incom
ing signal, but when a carrier or signal is present,
they beat with this carrier and produce a noise
in the loud-speaker or telephones. With a
square-law detector, this noise is proportional to
the carrier, or signal. The noise resembles the
sound of escaping steam and is called “shot- 5
effect noise” or brieñy “shot-noise”. Other causes
of noises in tubes and circuits also exist, but for
convenience they will all be referred to here as
shot-noise.
Since the shot-noise is dependent upon the 10
carrier voltage, it is evident that it will be con
stant regardless of the magnitude of the incom
ing signal wave so long as 'the input to the ñrst
amplifier is adjusted for a constant signal volt
age (or constant carrier voltage) at the detector. 15
The result of this is a constant signal to noise
ratio in the reception of all stations whether
local or distant when the volume is adjusted by
means of antenna coupling.
This constitutes a
decided drawback of the method as will be seen 20
presently.
i
Now turning to the other method, I have dis
covered experimentally that in general any ad
justment of electrode voltages in a vacuum tube
which reduces the amplification also reduces the 25
noise in proportion. Experimental evidence of
this in the case of an amplifier employing tetrodes
is shown in the curves reproduced in Figs. 1 and
2. Fig. 1 shows this close relation between shot
noise and amplification when the control grid 30
voltage is varied.
Curve A shows the relationship between the am
pliñcation and the control grid bias; the poten
tials applied to the other electrodesbeing constant.
Curve B shows the relationship between shot 35
noise and control grid bias for the same amplifier.
In Fig. 2, the curves C‘ and D represent the varia
tion of amplification and of shot-noise, respec
tively, with plate voltage. In all cases, the ratio
of amplification to shot-noise remains approxi
mately constant over the useful part of the
control range. The signiñcance of this is that
in controlling for constant output, the signal re
mains constant while the shot-noise decreases
continuously as the strength of the incoming 5
Wave increases, thus resulting in an improvement
of the signal to noise ratio for local stations. It
will be clear that from the viewpoint of noise
production this method is superior to the othe
the superiority increasing with the incoming sig- "
nal strength. The method has, however, the dis
advantage that as the voltage on the input of the
ampliñer tubes increases, a point is soon reached
at which the relation between input and output
2
2,134,747
voltages becomes non-linear and distortion re
sults.
I propose to retain the advantage of high sig
nal noise ratio of the amplification control
method, and to avoid the distortions which occur
in this method when the signal voltage is large
by employing a combination of the amplification
input voltage, and means for simultaneously ad
justing the said input and ampliñcation control
means.
4. In a radio receiver, a voltage divider for
determining the ratio of antenna voltage to
amplifier input voltage, a voltage divider for de
termining the potential applied to a volume cori
control and input voltage control methods. This , trol element of the amplifier, and means link
may be done by employing two controls, one of ing the movable contacts of said voltage dividers
10
to insure the simultaneous adjustment thereof.
10 each type, the two controls being so related that,
5.
In
a
radio
receiver,
a
radio
frequency
ampli
with increasing signal strengths, the antenna
control prevents the input to the first amplifier fier, an antenna control for regulating the input
tube from rising above the Value which would from a collector structure to said amplifier, a
control for adjusting an operating potential ap
produce distortion in the amplifier. It is prefer
able to simplify the receiver operation by linking plied to said amplifier to control thereby the
amplification of said amplifier, and means linking
these controls in such a way as to require but one
said controls to reduce the input to said amplifier
knob for adjustment.
as the amplification thereof is reducedn
Referring to Fig. 3 which illustrates an appli
6. The combination with an electrical signal
cation of the invention to a typical radio re
amplifier having an input circuit, an output cir 20
20 ceiver, the reference numeral l identifies the
voltage divider which determines the proportion cuit, and at least one electric discharge amplifier
of the antenna voltage which is applied to the device connected between said circuits for the
first amplifier tube. The amplification of the transmission of signals from said input to said
first tube is controlled by the control grid bias- output circuit, of means for varying the amplifi
cation of the amplifier device, means for varying
25 which is determined by the Voltage drop acrosS
the signal strength applied to said input circuit,
that portion of the voltage divider 2 which is in
cluded between the contact arm 3 and the and additional means for varying said last named
means simultaneously with said first named
grounded side of the voltage divider 2. This con
tact arm 3 and the contact arm 4 of the antenna
30 control are mounted upon a common operating
shaft 5 which carries a knob 6 or other conven
ient adjusting means.
S0 far as concerns the present invention, the
detailed construction of the radio receiver is not
35 important and may follow any usual Vor desired
design. The control of amplification may be
confined to a single stage, as in the circuit shown
in Fig. 3, or may include two or more stages. It
is also to be understood that the amplification
40 control may be obtained by varying the screen
grid or the plate potential since, as shown by
Figs. l and 2, a decrease in ampliflcation reduces
the shot-noise regardless of the particular op-'
erating potential which is adjusted to control the
45
amplification.
It will be apparent that there is considerable
latitude in the construction of amplifiers em
bodying the invention.
While I have indicated and described one ar
rangement for carrying my invention into effect,
it will be apparent to one skilled in the art that
my invention is by no means limited to the par
55
means.
7. The combination with an electrical signal
amplifier having an input circuit, an Output cir
cuit, and at least one electric discharge amplifier
device, connected between said circuits for the
transmission of signals from said input circuit
to said output circuit, of means provided with an 35
element movable between certain limits to vary
the transmission efliciency of said amplifier de
vice, means for varying the signal strength ap
plied to said input circuit, said last named means
being operative to reduce the signal strength ap fil)
plied to the input circuit as the transmission
efficiency of the amplifier device is being reduced
by said first named means, and a common means
for operating said second named means simul
taneously with said first named means.
8._The combination with an electrical signal
amplifier having an input circuit, an output cir
cuit and at least one electric discharge amplifier
device connected between said circuits for the
transmission of signals from said input to said à
output circuit, of means provided with an ele
ment movable between said limits to vary the
ticular organization shown and described, but
transmission eiiiciency of said amplifier device,
that many modifications may be made without
departing from the scope of my invention as set
a variable resistor, said resistor having a mov
forth in the appended claims.
I claim:
1. The method of controlling the output level
of a vacuum tube amplifier and increasing the
signal to noise ratio which comprises simultane
ously adjusting the amplification of the amplifier
and the magnitude of the signal voltage impressed
upon the same.
2. In the operation of a radio Vreceiver having a
radio frequency amplifier, the method of increas
65 ing the range of signal wave voltages that may
able element arranged to vary the signal strength
applied to said input circuit, the movement 0I"
said last named element being effective to vary
the signal strength as the transmission efñciency
of the amplifier device is varied, and means con
nected with said movable elements for moving 60
the same simultaneously.
9. The combination with an electrical signal
amplifier having an input circuit, an output cir
cuit and at least one electric discharge amplifier
device connected between said circuits for the
transmission of signals from said input to said
be transmitted without distortion, which com
output circuits, of means having a common con
prises simultaneously reducing the proportion of
the received signal voltage which is impressed
trol and provided with movable elements for
upon the amplifier and the amplification of said
of said amplifier device and the strength of sig 70
nals received by said input circuit.
10. The combination with an electrical signal
amplifier having an input circuit, an output cir
cuit and at least one electric discharge amplifier
device connected between said circuits for the 75
amplifier.
3. In a carrier wave amplifier, the combination
with means for adjusting the amplification of
said amplifier, of means for adjusting the pro
portion of received signal voltage to amplifier
simultaneously varying the transmission efficiency
2,134,747
transmission of signals from said input to said
output circuits, of simultaneously variable means
to vary the transmission emciency of said ampli
fier device and a signal voltage applied to said
input circuit, the range of movement of the
transmission eiiiciency varying means at least
equalling the range of control of the signal volt
age varying means in a direction of movement to
increase the transmission efficiency.
10
11. In the operation of radio receiving appara
tus utilizing thermionic tubes for amplifying radio
frequency signal energy, the method of eiiectingv
control of Volume of reproduction, which com
prises varying the transfer of radio frequency
15 signal energy between predetermined limits, and
simultaneously varying the amplification charac
teristic of at least one of said tubes.
12. In the operation of radio receiving appa
ratus utilizing thermionic tubes for amplifying
20 radio frequency signal energy, the method of
reducing the volume of signals which comprises
modifying the amplification characteristic of at
least one of said tubes to decrease the amplifica
tion of signal energy, and simultaneously de
25 creasing the transfer of signal energy.
13. In the operation of radio receiving appa
ratus utilizing thermionic tubes for amplifying
yradio frequency signal energy, the method of
reducing amplitude of signals which comprises
30 varying the potential applied to a control elec
trode of at least one of said tubes and simul
taneously decreasing signal energy transferred
to the input of said one tube.
14. In the operation of radio receiving appa
35 ratus utilizing thermionic tubes of the screen
grid type for amplifying radio frequency signal
energy, the method o-f varying volume of signals
which comprises varying the positive potential
applied to the screen grid of at least one of said
40 tubes, and varying the signal energy transferred
to the input of said one tube.
15. Radio receiving apparatus comprising at
least one thermionic amplifier tube of the screen
grid type, radio frequency input and output
circuits therefor, and a.- volume control ele
ment adjustable to vary both the positive bias
ing potential of the screen grid of said tube and
the magnitude of transfer of signal energy to the
input circuit thereof.
16. Radio receiving apparatus comprising a
3
screen grid amplifier tube, input and output
circuits for said tube, a resistance in the input
circuit, a resistance in the screen grid circuit
of said tube, means for effecting iiow of direct
current through said second resistance to main
tain the screen positively biased with respect to
the cathode of the tube and a volume control
element adjustable simultaneously to vary in
the same senses the effective magnitudes of said
resistances cumulatively to effect change in Vol 10
ume reproduction.
17. The method of controlling the output en
ergy of a vacuum tube amplifier which com
prises simultaneously controlling amplification
of the tube and the amount of input signal
supplied thereto.
18. The method of controlling the output en
ergy of a vacuum tube amplifier which com
prises simultaneously varying the bias potential
applied to the input circuit of the tube and the
amount of input signal supplied thereto.
19. In an amplifier system, in combination, a
vacuum ~tube amplifier, resistance means for
controlling the bias. voltage applied to the signal
input grid of said tube, resistance means for
controlling the signal input voltage applied there
to, and a single means for adjusting both said
control resistance means.
20. The method of controlling the output en
ergy of an amplifier device incorporating at 30
least one electronic tube, which method consists
in reducing the amplifying action of the elec
tronic tube and at the same time reducing the
amount of input signal energy applied to the
amplifier.
35
21. The steps in the method of controlling
the output energy of amplifying apparatus which
is coupled to a source of signal voltage and which
includes at least one amplifying tube which
comprise increasing the amplifying action of the 40
tube and simultaneously increasing the coupling
between the amplifier device and the source _of
signal voltage in order to increase the output
energy of the ampliñer device and decreasing
the amplifying action of the tube and simultane 45
ously decreasing the coupling between the am
pliiier device and the source of signal energy to
decrease the output energy of the amplifier de
vice.
STUART BALLANTINE.
50
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