US1397862A

US1397862A - Transmission system

Info

Publication number: US1397862A
Application number: US203949A
Authority: US
Inventors: Albert L Fitch
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1917-11-26
Filing date: 1917-11-26
Publication date: 1921-11-22
Anticipated expiration: 1938-11-22

Description

A. L. FITCH.

TRANSMISSION SYSTEM.

APPLICATION FILED NOV. 26, 19H. RENEWED DEC. 26. 1918.

1,397,862, Patented Nov. 22, 1921.

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ALBERT L. FITCH, OF EAST ORANGE, NEW JERSEY, ABSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A COMORATION 'OF NEW YORK.

TRANSMISSION SYSTEM.

Application filed Kovember 26, 1917, Serial No. 203,949. Renewed December 26, 1918. Serial No. 288,420.

' for connecting a transmitter to an electron discharge device such as a vacuum tube amplifier. Previous to this invention it has been proposed to connect a condenser transmitter to a vacuum tube amplifier, and also to use a single battery or source of electromotive force, both in the output circuit of the amplifier and as a means for polarizing the transmitter.

A condenser transmitter of a well-known type consists of two-electrodes, one of which is conductively connected to an outer shell or casing usually made of metal. This casing is subject to being touched or otherwise accidentally or inadvertently grounded, thereby grounding the electrode. Since, in the ordinary operation of a vacuum tube amplifier of the three-electrode type with a single battery as referred to above, the filament usually is grounded in order to secure good operation, any such accidental ground ing of the transmitter case would cause either the battery or the condenser transmitter to be short-circuited and thus interfere with the operation, as well as being a source of inconvenience or danger. It is a particular object of my invention to remedy this defect by so relating the battery, which performs both the functions of charging the condenser and furnishing current to the output circuit, with circuits and apparatus that one. electrode of the condenser transmitter may always be grounded during normal operation. As the other electrode is insulated within the case, it is not likely to be grounded. While this invention is preferably used in connection with apparatus in which a common source of electromotive force polarizes the transmitter and operates the amplifier, it is not peculiar to such an arrangement, but, broadly stated, is directed to the combination of a condenser transmitter Specification of Letters Patent.

to function as an amplifier, is associated with the condenser transmitter conventionally dia'grammed at T, in which electrode t is-the movable or vibratory plate against which sound waves impinge and t is the fixed electrode. We may assume that in this transmitter, the electrode t is uninsulated from the metallic case a which contains it and also has its exterior surface exposed, while electrode 25 is mounted upon the interior of-the transmitter and is insulated, as represented by the supporting insulation material -1. Plate 25 is connected to the filament or cathode 2 of tube A by conductor 3, while plate t is connected to grid or control electrode 4 by conductor 5, in which is placed condenser C. Plate t is also adjustably connected to battery B at the positive terminal by conductor 6, while conductor 3 is continued to connect with the negative terminal of the battery B. A battery 7 is connected between the grid and filament to keep them at a proper relative potential and an impedance in the form of the high resistance 8 is connected in series with this battery. This resistance functions to prevent a" short circuit between the plates of transmitter T. For satisfactory operation, resistance 8 should be of such a value that the minute differences of fiuctuating potential existing across filament 2 and grid 4, would not cause an appreciable flow of current through resistance 8 in the time occupied by one complete fluctuation. In a particular instance resistance 8 had a value'of one megohm. The plate or anode 9 of tube'-;A is adjustably connected through a suita'ble'conductor 10 to the positive terminal of battery B, which is thus in series in the output circuit of the tube A. A transcuit of any part of the apparatus.

' either electrode may be grounded, it is preferred to ground the one which is most exposed. Condenser O is of large capacity so that its impedence is negligibly small in comparison with the input impedance of the amplifier A.

The parts of the multi-stage amplifier circuit of Fig. 2 correspond in general to Fig. 1, andthe above description is applicable thereto except as mentioned. The battery B is also used as a source of direct current in the plate-filament circuit, for a second amplifier A. The direct current of the plate-filament circuit of amplifier A passes from late 9 to filament 2, through resistance 1 and battery B, while the alternating voltage is impressed across both of resistances 17 and 14:. The variations of drop in voltage across resistance 14 are impressed upon the amplifying tube A and further amplified. The direct current path in the output of A is from plate 9', through resistance 15 and battery B, to filament 2, while the amplified alternating current variations are impressed upon a line 12 by a transformer 11 as in Fig. 1.

The disclosure herein of particular means for carrying out the invention should not I be interpreted to limit the invention to electrodes of said condenser at different relative potentials, and means for impressing the alternating current due to variation of the said capacity upon an amplifying device, said amplifying device being supplied with operating current by said source of electrical potential, said condenser having one electrode thereof grounded through a path of negligible resistance, the characteristics of said path being such as to keep said electrode at ground potential.

2. In combination, a condenser transmitter with an electron discharge device, one

tially ground potential.

terminal of the transmitter being permanently at ground potential and a source of electromotive force common to a circuit fy through the condenser transmitter and the output'circuit of said device.

3. In combination, a transmitter for changing sound waves into waves of electrical current, an electron discharge device for'said current waves, a common source of electrical energy arranged to energize said transmitter and to furnish operating current for said device, and a path from one terminal of said transmitter to ground, the characteristics of said path being such that saiil one terminal is kept at ground potentia L. In combination, two electrodes 'constituting a transmitter for changing sound waves into waves .of electrical current, an electron discharge device for said current waves, a common source of electrical energy arranged for polarizing said transmitter and for furnishing voltage to said device, one of said electrodes being grounded through a path, the characteristics of said path being such as to keep said electrode at substan- 5. In combination, a transmitter for changing sound waves into electrical waves, an amplifier for said electrical waves, and a common source of electrical potential for polarizing said transmitter and supplying operating current to said amplifier, said transmitter having a terminal grounded through a conducting path, the characteristics of said path being such as to keep said terminal at substantially ground potential.

6. In combination, a transmitter for changing sound waves into electrical waves, a-vacuum tube, and a common source of electrical potential for energizing said transmitter and supplying voltage to said tube, a terminal of said transmitter having a ground connection, there being no conducting path through said ground connection from one terminal of said transmitter to the other terminalthereof.

7. In combination, a device having two electr'odes which constitute an electrical capacity, one electrode being free to vibrate, the vibrations thereof causing variations of electrical capacity in said device corresponding to the said vibrations, a source of electrical energy for charging said capacity, a conductor, and means whereby said vibrations of electrical capacity cause a varying current in said conductor, an amplifier for said current, said source of electrical energy furnishing operating current for said amplifier, one of said electrodes being grounded through a path whose nature is such as to keep said electrode at ground potential.

8. In a device for transforming sound waves into amplified electrical waves, a transmitter connected in series between two electrodes ofihn electron discharge device, a comparativly high resistance forming a shunt circuit around said transmitter, and a second shunt circuit extending from a terminal of said transmitter through a source of potential to one of said electrodes, said source of potential also being connected serially in the output circuit of said electron discharge device.

9. Means for transforming sound waves into amplified electrical waves, including a transmitter connected in circuit with a source of electrical energy and two elements of an electron discharge device, a resistance external to said device connecting said elements, said source of potential being in a series circuit connecting one of said elements with a third element of said electron discharge device, and a conducting path of negligible resistance from a terminal of said transmitter to ground, the characteristics of said path being such as to keep said terminal at ground potential.

10. In a device for transforming sound waves into electrical waves of considerable amplitude an electrostatic transmitter whose electrodes are respectively connected to the filament and grid of a three-element electron discharge device having a grid, a filament and an anode; the connection to said grid containing a condenser whose impedance is negligible in comparison with the impedance of the input circuit of said device, and a comparatively high resistance directly connecting said filament and grid, said electrode which is connected to. said grid being connected to said filament through a shunt circuit containing a resistance and a source of electromotive force, said source being located serially in circuit with said filament and said anode of said electron discharge device. l

11. In combination, two electrodes constituting a transmitter for changing sound waves into waves of electrical current, a

vacuum tube, a common source of electrical energy arranged for polarizing said transvmitter and for furnishing voltage to said vacuum tube, one of said electrodes being grounded through a path having no source of electromotive force contained therein.

12. In combination, a condenser transmitter having two electrodes, one of said electrodes being connected to a cathode of an electron discharge device, the other of said electrodes being connected to a control electrode of said device, and means whereby a terminal of said cathode and one of said condenser electrodes are maintained at ground potential. v

13. The combination with a vacuum tube having a source of voltage, of a circuit comprising a condenser transmitter, said source of voltage and a high resistance, said transmitter having an electrode connected to ground through a low impedance path.

14. In an electric system, a clrcuit containing a source of voltage, a condenser transmitter having an electrode connected to ground through a path of negligible impedance, and means for impressing upon an outgoing line the electrica variations produced in said circuit by said transmitter.

15. In an electric system, a circuit containing a source of voltage and a transmitter having a pluralitypfelectrodes, one of said electrodes being connected directly to ground, means for impressing upon a second circuit containing said source of voltage the electrical variations produced in said first circuit by said transmitter.

16. A condenser transmitter having a plurality of electrodes, a metallic casing, one of said electrodes being connected to said casing, a source of voltage, and a grounded connection between said source and said casing.

17. The combination with a vacuum tube, of a condenser transmitter having a plurality of electrodes, a metallic casing, one of said electrodes being connected to said casing, a source of voltage, a grounded connection between said source and said casing, and means for impressing upon said tube the electrical variations produced in said transmitter.

In witness whereof, I hereunto subscribe my7name this 20th day of November A. D., 191

ALBERT L. FITCH.