Патент USA US2412279код для вставки
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.