US1768661A - Signaling system - Google Patents

Description

July 1, 1930. w, BRlNDLEY 1,768,561

SIGNALING SYSTEM Filed July 1928 INVENTOR William E. Bnindley I ATi'OREY 'Fat ented July 1, l3

WILLIAM BRINDLEY, F WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC 8c MANUFACTURING COMPANY, A C ORPORATION OF PENNSYL- VANIA SIGNALING SYSTEM Application filed July 7, 1928. Serial No. 291,019.

' My invention relates to signaling systems.

and apparatus, and it has particular relation to apparatus for the conversion into sound of electrical impulseslocally derived from phonograph records, or irnpulses derived from high-frequency signals received from i a distance.

Apparatus of the general type to which my invention pertains is illustrated in the patent 10 to Craft, N 0. 1,559,679, wherein means are disclosed for preventing injury to the filaments of the thermionic amplifier tubes when a change is made from radio-signal reception to phonograph operation. 1 The system disclosed in the above-mentioned patent, while successfully accomplishing the objects of the patentees invention, in

so far as the thermionic tubes available at the time his application was filed are concerned, is inadequate to prevent signal distortion and possible injur to the thermionic tubes in modern radio-p ionographs, which tubes are often operated at plate-potentials as high as 450 volts. 1 c

The employment of high plate potentials, which are usually derived from B-eliminators of well known design, necessitates correspondingly large negative grid-biasing potentials, and, if the apparatus is to be prevented from distorting the signals, whether locally derived or received from a distance, it is imperative that the balance between grid-biasing potentials and plate potentials be accurately maintained, irrespective of the signal source.

A B-eliminator, as usually constructed, comprises a rectif ing device, a filter chain, and an output resistor. Plate potentials for the thermionic tubes comprised in the radioreceiving portion of the radio-phonograph, as well as plate potentials for the thermionic tubes comprised in the amplifier portion common to both the radio-receiving portion and the phonograph portion of the apparatus, are derived from the output resistor. Grid-biasing potentials for all of the tubes are usually derived from the output resistor as well, the connections for this purpose being shown in the patent to Aceves, No. 1,622,170.

/ When the apparatus is shifted from radio reception to phonograph-record reproduction, the plates of the tubes comprised in the radio-reception portion are disconnected from the out-put resistor and, consequently, the decreased flow of current through the said resistor, occasioned thereby, tends to cause increased potentials to be applied to the plates of the tubes in the amplifier portion of the apparatus. I

It is, accordingly, an object of my invention to provide means for automatically maintaining correct potentials on the plates of the thermionic tubes comprised in the amplifier portion of a combined radio-phonograph, irrespective of the source of signals being amplified. Q

A successful commercial embodiment of my invention consists of a radio-signal-receiving portion comprising a plurality of thermionic devices of the type having cathodes capable of being energized by alternating current, an audio-frequency amplifying port-ion comprising a plurality of poweramplifying tubes, a device for delivering unidirectional current to an output resistor from which plate potentials for the several thermionic tubes are derived, a pick-up device for deriving electrical impulses from a phonograph record, and a switching device for shifting the amplifier from radio-signal reception toactuation from the pick-up device. v

The switching device, in addition to the contacts necessary for controlling the aforementioned shifting, is further provided with an additional set of contacts which, when it is desired to electrically reproduce a phonograph record, serve to so establish a short circuit around a portion of the aforementioned output resistor that unduly high potentials cannot be developed thereacross and applied to the plates of the tubes in the amplifier portion.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organizationand its method of o eration, together with further objects an advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing.

The single figure of the drawing is a diagrammatic view of the essential apparatus and circuit connections constituting a radiophonograph comprising a preferred embodiment of my invention.

The apparatus illustrated in the drawing comprises a plurality of thermionic amplifying devices 1, 2 and 3, and a thermionic detector 4, which together constitutes means for producing low-frequency currents from incoming high-frequency signals, and a plurality of themionic devices 5 and 6 which constitute a low-frequency amplifier.

The cathodes of the thermionic devices 1, 2, and 3 are connected, in parallel, to the terminals of a secondary Winding 7 of a power transformer 8, by means of a plurality of conductors 10 and 11. The thermionic device 4 is of the unipotential type, having an eleetronic-emissive cathode 12 and a heator element 13. The heater element is connected to the terminals of a secondary winding 14 of the power transformer.

The cathode of the power-amplifying thermionic device 5 is connected to the terminals of a third secondary winding 15 of the power transformer, while the cathode of the last power-amplifying thermionic device 6 is connected to the terminals of a fourth secondary winding 16.

' The power transformer is provided with a primary winding 17 which may be connected to any convenient source of commercial-frequency alternating current, and is further provided with a secondary winding 18 arranged to supply filament potential to the cathodes of a plurality of rectifying devices 19 and 20, plate potential for Which devices is supplied by an additional secondary winding 21. The rectifying devices are provided with an output circuit which may be traced from a midpoint on the secondary winding 21, through the field winding 22 of a loud speaker 23 of the electro-dynamie type, an output resistor 24, an inductor 25 and thence to the filament-heating transformer winding 18. A plurality of condensers 26, 27 and 28 are disposed in shunt to various portions of the output to resistor 24 to provide paths ofi'ering low impedance to high-frequency currents, and a plurality of condensers 30 and 31, of large capacity, are connected in shunt to the output terminals of the rectifier-to provide a filter circuit which assists in eliminating the commercial-frequency hum.

Neither the exact manner in which the first thermionic tube of the radio-frequency receivingportion of the system is connected to an antenna structure 32 nor the specific manner in which the several radio-frequency .tubes are interconnected in cascade through radlo-frequency transformers 33, 34 and 35 constitutes an essential part of my invention.

The specific type of rectifier utilized is also immaterial, although it is preferable to use a rectifier of the full-wave type.

The apparatus just described is preferably disposed in a phonograph cabinet of any usual and well known type (not shown) in which cabinet is provided a rotatable turntable 40 adapted to support a phonograph record 41. An electro-dynamic or microphonic pick-up device 42 is provided which, when actuated by the phonograph record, causes fluctuating potentials to appear across an output resistor 43 which is connected across the terminals thereof.

In addition, I provide a switching device 44 comprising a cam 45 pivotally mounted upon a pin 46 and havingassociated with it a plurality of flexible contact elements 47 and 48. A plurality of fixed contacts 50 and 51 are associated with the flexible contact member 47, and a plurality of similar fixed contacts 52 and 53 are operatively associated with the flexible contact member 48.

The cam 45 may be'so. turned about the pin 46, by means of a handle 54, that the flexible contacts 47 and 48 may be caused to engage either of the fixed contacts associated therewith. When it is desired to actuate the amplifier portion of the system from an incoming radio signal, the handle is moved in from the fixed contact 51 and to engage the fixed contact 50. At the same time, pressure upon the flexible contact member 48 being released, it disengages from the fixed contact 53 and moves inwardly to engage the fixed contact 52. Plate potential is, accordingly, applied to the thermionic devices 1, 2 and 3 over a circuit which may be traced from a point 60 on the output resistor 24, through a conductor 61, the flexible contact 47, the fixed contact 50, and a conductor 62. At the same time, plate potential is applied to the detector device 4 over a circuit which may be traced from a point 63 on the resistor 24, through a conductor 64, the primary winding 65 of an intertube transformer 66, a conductor 67, the flexible contact member 48, the fixed contact member 52, a conductor 68 and a radio frequency choke coil 70.

Plate potential for the thermionic device 5 is supplied from the point 60 on the resistor over a conductor 71 and the primary winding 72 of an intertube transformer 73.

Plate potential for the power-amplifying device 6 is supplied from a point 74 on the output circuit of the rectifier over a conductor 75, the primary winding 76 of an output transformer and a choke coil 77 which, together with a plurality of condensers 78 and 80, constitutes a tone filter.

connection 91 extends from an intermediate point thereon to a point 92 near the negativeterminal of the resistor 24. The grid of the same amplifying device is connected, over a conductor 93, to the negative terminal of the resistor 24, thusmaintaining a biasing potential thereon which is negative with respect to the filament by an amount equal to the potential drop across the portion of the resistor comprised between the point to which the conductor 91 is connected and the negative terminal.

A resistor 100 is connected in shunt to the filament of the second amplifier deyice 6, and the grid of the same device is connected to an intermediate point thereon through a resistor 101, preferably having a resistance of 1450 ohms. Inasmuch asthe space current in the said thermionic device traverses the resistor 101, the grid of the device is always maintained at a potential negative with respect to the filament by .an amount proportional to the average plate current. Such an arrangement tends, to some extent, to stabilize the output of the thermionic device unless the plate potential applied thereto is unduly increased.

When it is desired to actuate the amplifier portion of the system from a phonograph record, the handle of the switching device is moved in the direction of the arrow B. The

flexible contact member 47 accordingly, leaves the fixed contact 50, thus depriving the tubes 1, 2 and 3 of plate potential, and the flexible contact member 48 is forced out of engagement with the fixedrcontacts 52 to remove plate potential from the detector tube 4, and is caused to engage the fixed contact 53, which contact is connected to a movable arm 105 associated with the resistor 43 included in the output circuit of the pick-up device 42. By reason of the engaging of the flexible contact member 48 with the fixed contact 53, the resistor 43 is connected in parallel with a portion of the primary winding 65 of the coupling transformer 66 over a circuit including a conductor 106 and the conductor 67, previously referi'ed to.

The flexible contact 47 by engaging the fixed contact 51, establishes a shunting path, including the conductor 61 and a conductor 107, around a portion of the resistor 24,- and effectively moves the point on the resistor, from which plate potential isderi'ved for the first amplifier tube 5, toward the negative end of the said resistor.

By reason of the fact that the thermlonic devices 1, 2, 3 and 4 are deprived of plate potential when the system is shifted from radio reception to phonograph-record actuation, the load upon the rectifier is decreased, and the potential applied to the first low-fre. queney amplifier tube 5 would attain too high a value were it not for the shunt connection just described. The shunting connection, however, compensates for the reduced load on the resistor and serves to maintain the plate potential on the first amplifier tube at substantially the same value that it had before the system was shifted from radio re ception to record actuation.

The magnitude of the resistor 24 is determined by the type of rectifier employed and by the potentials required for the amplifier tubes. In one successful embodiment of my invention, wherein the first audio amplifier. tube is of the type known as UX226, the resistor 24 has a magnitude of 14725 ohms, and the normal potential of the point 60, with respect to the point 92 thereon, is of the order of 135 volts. The increase in current through the resistor occasioned by disconnecting the plates of the thermionic device 1, 2, 3 and 4 is of the order of 12' milliamperes, and that portion of the resistor shunted by the contacts 48 and 53 of the switching device is approximately 2250 ohms.

It will, accordingly, be apparent that I have provided, by my invention, a valuable improvement over the system disclosed in the Craft patent hereinbefore referred to. Inasmuch as the provision of the shunting path around the output resistor of the voltage sup ply prevents unduly high potentials from being applied to the amplifier tubes, when the system is shifted from radio-signal reception to phonograph-record actuation, the life of the tubes is materially longer than if the compensating shunt were not present. In addition, by maintaining the plate potentials applied to the audio-frequency amplifying tubes always at the proper values with respect to the grid-biasing potentials applied thereto, overloading of the tubes, when energized from a phonograph record, is prevented, and the quality of the sound output from the apparatus is kept much better than that from analogous devices with which I am familiar.

Although I have illustrated my invention as being particularly applicable to a system comprising high-frequency amplifying stages of a particular type and a detector stage comprising a thermionic device of the unipotential variety, it is to be understood that the invention is not to be limited thereto. As many stages of amplification as are desired may be employed, either for the amplification of the radio signals or for the amplification of the audio-frequency currents produced by the detector or derived by the pick-up device from the phonograph record. It also lies .within the province of my invention to apply My invention, therefore, is not to be limited 1 except in so far as is necessitated by the prior art or by the spirit of the appended clalms.

I claim as. my invention:

1. In combination, means, including a thermionic device, for deriving electrical impulses from received radio signals, means for. deriving electrical impulses from a sound-record, means, including a thermionic device, for amplifying electrical impulses, a common source of potential for the platesof said thermionic devices, connections where by either of said electrical-impulse-deriving means may be associated with said amplifying means, and additional connections so changeable with the first-named connections that the potential applied to the plate of the thermionic device comprised in said amplifying means is maintained substantially constant, irrespective of which impulse-deriving means is associated therewith.

rality of thermionic devices, for receiving high-frequency signals and translating them into low-frequency signals, an amplifier comprising a plurality of thermionic devices, an electrical phonograph reproducer, a common source of plate potential for all of said therone position, connects said receiving means to said amplifier and applies plate potential from said source to all of said devices and, in a second position, disconnects said receiving means fromsaid amplifier, connect-s said phonograph reproducer to said amplifier and deprives the thermionic devices in said receiving means of plate potential, and means for preventing the application of excess plate potentials to the thermionic devices in said amplifier when the latter is connected to said phonograph reproducer.

' 3. In combination, a source of unidirectional current, an impedance device contnected across the terminals of said source, a load comprising the plate-filament paths of a plurality of thermionic devices, means for fractional portion'thereof in shunt to said impedance device or a portion thereof, and means for so altering said connections as to prevent excess voltage from being applied'to said. portion when so connected to said impedance device.

4. In combination, a source of unidirectional current, an impedance connected across the terminals of said source, a load comprisin the plate-filament paths of a pluralit of t ermionic devices, means for connecting either the whole of said load or a portion thereof in shunt to said impedance device, and means for establishing a shunt path around a portion of said impedance device when less than the whole of said load is connected thereacross, whereby the application of excess potentials to said fractional load is prevented. a Q

mionic devices, a switching device which, in r connecting either the whole of said load or a 5. In combination, means for deriving unidirectional current from an alternating-current source, an impedance device through which said unidirectional current may be caused to pass, a load comprising the platefilament paths of a plurality of thermionic devices, means for connecting either the whole of said load or a fractional portion thereof in shunt to said impedance device, and means actuated by'said connecting means for establishing a shunt path around a portion of said impedance device when less than the whole of said load is connected thereacross, whereby the application of excess potentials to said fractional load is prevented.

In testimony whereof, I have hereunto subscribed my name this 28th day of June, 1928.

WILLIAM E. BRINDLEY.

2. In combination, means, including a plu-

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