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Патент USA US2412279

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Dec. l0, 1946.
D_ ¿_ MULLER»I JR
2,412,279 _
VARIABLE GAIN AMPLIFIERFiled June 28, 1944
Elo/nils?, nací
W
y J.
M
5
IN VEN TOR.
Patented Dec. 10, 1946`
UNITED STATES PATENT lOFFICE
2,412,279
„
VARIABLE GAIN ALIPLIFIER
David J. Miller,
Jr., Philadelphia, Pa., assignor,
by mesne assignments, to Philco Corporation,
Pa., a corporation oi'
vani
Application June 2s, 1944, serial No.
10 Claims.
Pennsyl
542.460
2
amplifiers especially adapted for use
in television systems. More particularly the
tube and head amplifier, represented at il, which
signal is transmitted to a blankl
invention relates to improvements in a variable
“fading” the
A variable gain
disclosed
and
claimed in U. S. Patent No. 2,233,317,
granted
February 25, 941, to P. J. K
assigned
to the assignee of the present application. The
present
the
said invention
patent. is an improvement over that of
In the said Konkle patent there isgdisclosed a
fading amplifier c
era tube and head amplifier lG'supplies a video
signal to a bianking out and fading ampliñer l1
which is also connected to the composite signal
16
20
amplifier in response to the blan
functions. While the device is
25
and hence 'the television receivers may
tained in synchronism with
mitter.
30
ing the operation of the system.
The principal object of the
fore, is to provide an improved invention, there
fading amplifier.
blan
out and 35
illustrated a preferred form
and fading amplifier pro
vided by the present invention, which may be em
. 1.
40'
be apparent from th
conjunction with the accompanying drawing, in
which:
Fig. 1
45
channel television transmission
the present invention may be applied; a
50
To facilitate a clear and complete understand
ing of the invention, reference may ñrst be
.
In a conventional television system a
video or picture signal is obtained from a camera
voltages of the tubes 24
“Virt
om
ue of a common anode resistor 34,
2,412,279
4
the blanking signal tends to
output signal is derived by way
pacitor 35. An inductor 36 preferably is inter
posed between the common anode resist
tion of the balanced amplifier to prevent. The
undesired components tend to distort the video
34 and
signal during the fading operation, and may even
the source of anode potential 29, in order to min
imize the effect of the
pacities of the tubes.
affect the synchronization deleteriously.
'
_
coupling condenser and the inter-electrode ca
28 may be so ad
‘on of an;1 video sißllal
produce undesired .
' output components, whose presence it is ~the func
present invention,
by fading out
I foregoing obiection is overcome
the potentiometer
43
The value of the resistor
is operated in a
justed that the
amplifica
branch
of the ampiiñer including 1o signal. 'To this end there is provided an addi
'the tubes 23 and 32 is the same as the ampliñoa
tion of any input signal through the other branch
tional tube 44 having a coupling capacitor 45 con
nected to the source of blanking out signal. The
tube 44 has an anode resistor 46 connected to
the source of anode voltage and is coupled to
tube 31 through condenser 4i. The cathode of
tube 44 is connected to ground, and its grid-to
cathode circuit is completed by a grid resistor
41 connected to an adjustable contact on a
amplifier may
potentiometer 48 which is connected
between
of bias voltage. It
bias voltage appearing 20
be varied by varying the
that opposite ends of the poten
across the common cathode resistor 21. To this
tiometers 4B and 43 are connected to ground and
end, there is provided a vacuum tube 31 having
that the dotted line representation between the
a cathode circuit which includes the resistor
adjustable contacts thereof indicates a common
21. The anode of tube 31 is connected
to
the
an anode re- 25 control for the two potentiometers. The tube 44
gI-‘Ollnd by
preferably is a small triode, such as a 6J5G,
sistor 38 which may
whereas the tube 31°may be a larger triode, such
a capacitor 39.
as a 6AC5-G or a beam power amplifier such as
be applied to t grid of the
a 6V6. By this arrangement, tube 44 is biased
coupling capacitor 4l. The grid circuit of tube
42 connected to an 30 to cut off when potentiometer 43 is operated in
31 includes a grid resistor
a direction to apply a more positive voltage to
adjustable contact of a voltage divider or poten
the grid of tube 31, By careful selection'of the
tiometer 43 which has one terminal connected
values of the potentiometer resistances, the blank
to ground and the other terminal
be caused to fade out before it
the negative
The blanking out
4| periodically raises the
When direction to fade in the video signal, the
opposite
of tube 31 and causes increased
circuit, thereby
blanking signal
tiometer 4B, and when the normal setting of
across the resistor
23 and 40 potentiometer 43 is reached the balanced condi
21 and effecting periodic cutoff of tubes
tion of the amplifier is restored.
24. Whenever desired, the video signal may be
faded out or in by manipulation of the poten
scribing the present invention a certain preferred
tiometer 43 which varies the gain of tubes 23
and 24 by varying the current flow through re- 4vY specific embodiment has been shown,
sistor 21.
.
The variable gain
scribed corresponds substantially to that shown in
the aforementioned Konkle patent. Such an am
piiiier, while generally satisfactory,
as may be commensurate with the scope of the
appended claims. ì
I claim:
ency to become unbalanced when the fading po
tentiometer 43 is operated. It is practically
im
use as tubes
balanced condition for different adjustments of
the potentiometer 4
understood that the invention is not to be limited
thereby since such variations are contemplated
‘
`
t
_ l. In a television system, a video signal ampli
fier, means responsive to a control signal for
varying the gain of said amplifier, manually
operable means for varying the gain of said am
plifier from a normal value to substantially zero
or vice versa, whereby'the video signal may be
faded out or in, and means operable coniointly
with said last-named means for preventing the
is working into a plate load which is common
with tube 32 while tube 23 is working into its own
control signal from deleteriously affecting the
plate load. This diiiiculty is further aggra
amplifier during the fading operation.
vated by the fact that tube 23 is coupled to the
2. In a television system, a video signal ampli
through condenser 3| which re- 60
grid of tube 32
iler, a control signal source, means responsive to
moves the D. C. component and causes the sig
said control signal for varying the gain of said
nal on the grid of tube 32 to operate about the
amplifler, manually-operable means for varying
grid bias level of that tube, whereas tube 24
is D. C. coupled to the output circuit and pre 65 the gain of said amplifier from a normal value
to substantially zero or vice versa, whereby the
video signal may be faded out or in, a vacuum
The amplifier may be adjusted, as previously
tube interposed between said control signal sourcey
and said amplifier, and means for reducingthe
the potentiometer 43, and as long as the poten
tiometer adjustment remains the same, the sys 7 0 conductivity of said tube during operation of said
manually-operable means to reduce the gain of
tem will maintain its balanced condition. But
said
ampliñer.
when the potentiometer adjustment is varied, e. g.
3. In a television system, a video signal ampli
to fade the video signal out, the system tends
fier, a control signal source, means responsive to
to become unbalanced for the reasons stated
for varying the gain of said
above. 1f the blanking signal were not present, 75 said control signal
described, for operation
setting of
this would be immaterial, but the presence of
2,412,279
signal by said vacuum tube.
4. In a video signal ampliiler fora television
. .it
control voltage, said voltage being applied to 15 common cathode circuit, a resistor in said com
ably biasing said ñrst tube to fade the video signal 20 ampliñer substantially to zero, manually-oper
channels, an amplifier in each of said channels, 25 responsive to the fading operation for preventing
the blanking signal from introducing such ef
ond auxiliary vacuum tube interposed between 30 plifier circuit constructed and arranged to trans
to reduce
the gain of said amplifier
of said auxiliary vacuum tubes, whereby the video 40 to
zero, manually-operable
means substantially
for variably
signal of one channel may be faded out and the
'
nal7. may
be fadedout
outand
andfading
in.
A blanking
amplifier for use
biasing said gain control tube so as to fade the
video signal out or in, said blanking signal tend
gain offorsaid
amplifier,
and ofmanually-operable
means
varying
the gain
said am liñer to
DAVID J. MILLER. JR.
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