US2062888A - Radio receiver - Google Patents

Description

Dec. 1, 1936.

E. L. KOCH RADIO RECEIVER Filed April 16, 1931 INVENTOR EARL L. KOCH.

ATTORNEY Patented Dec. 1, 1936 UNITED STATES RADIO RECEIVER Earl L. Koch, Chicago, Ill., assignor, by mesne assignments, to Radio Patents Corporation, New York, N. Y., a corporation of New York Application April 16, 1931, Serial No. 530,555

7 Claims.

This invention relates to improvements in radio receivers; especially of the kind used in broadcasting, with a loud speaker attached.

An object of the invention is to provide a radio receiver containing a novel form of vacuum tube so connected that the receiver can be exceedingly simple in design and quite inexpensive to produce.

A further object is to provide a radio receiver wherein the vacuum tubes of the various stages are all of the external-grid type, of restricted dimensions, but relatively large output; and low in the cost of both manufacture and operation.

Another object of the invention is to provide a radio receiver of this character having vacuum tubes of such construction and arrangement that the grid of each tube can be operated at the same steady direct current potential as the anode of the preceding tube; so that the usual grid blocking condenser may be omitted, and the various tubes can all be united by direct impedance coupling.

A still further object is to provide a radio receiver of such design that the filaments of all the vacuum tubes including the detector can be energized with alternating current derived from any convenient source.

An additional object is to provide a radio receiver which can be utilized with any sort of telephone or loud speaker, but which is preferably adapted to be employed with an electrostatic loud speaker with a source of polarizing voltage.

These and other objects and advantages will be more fully set forth in the following description, taken with the drawing, which illustrates one of the many possible embodiments of the principle of my improved receiver. This disclosure, however, is illustrative only, and the details of structure and function may be varied, without exceeding the scope and spirit of the invention, as defined by the broad and specific meanings of the terms in which the appended claims are expressed.

The drawing shows in diagrammatic outline a radio receiver having the characteristics of my invention.

Numeral I indicates a receiving antenna connected to a radio frequency coupling stage comprising a vacuum tube 2 consisting of a glass or similar container housing a cathode of the heated variety and a cooperating anode; but with the grid on the exterior of the container and united directly with the antenna I. A second radio frequency tube 3 is coupled to the tube 2 via a selector circuit which will be described more in detail later. Audio frequency tubes are indicated at 4 and 5, with a gas-filled detector at 6.

The tubes 3, 4, 5 and 6 are all like the tube 2 with outside grids; and the receiver thus includes two stages of radio frequency amplification, and two stages of audio frequency amplification, with the detector 6 between the stages. At I is a volume control device comprising a potentiometer resistance in the antenna, with an adjustable connection to the grid of the tube 2.

To energize the filaments of the tubes abovementioned, alternating current is led through mains 8 to the primary coil 9 of a suitable transformer, having a secondary II] to which allthe filaments, including that of the detector 6, are

joined in parallel. The same transformer has another secondary winding II, connected to the filament of a two-element vacuum tube half-wave rectifier I2. A third secondary winding I3, of v the transformer has one of its terminals con- 20 nected to the anode of this rectifier; so that, as subsequently explained, the plates or anodes of all the tubes 2, 3, 4, 5 and 6 may be supplied with direct current. The filament of the rectifier is connected through a lead I4 to'a. common conductor I5, to which the anodes of the tubes 2, 3, 4 and 5 are all united in multiple. The lead I4 may contain a suitable inductance I6. A conductor I'I, joined to the antenna I, is united at its other extremity through the conductor I8 to the remaining terminal of the secondary I3; and across the secondary I0, is placed a resistance I9 united to the conductor I8 at its middle. The connections from the conductor I5 to the plates of the tubes and the conductor II are bridged by suitable condensers 20; and across the leads I4 and I5 is a condenser 2I to cooperate with the inductance I6 and smooth out the unidirectional current produced by the rectifier I2. All of the connections to the plates of the vacuum 6 ' tubes 2, 3, 4, 5 and 6 include impedance in series, and the anode circuit of the detector may also contain a small resistance 22. T

The grids of the tubes 4, 5 and 6 are each directly connected with the plate of the preceding tube; and as each grid is insulated by the material of the container from the filament and anode associated therewith, no grid blocking condenser or coupling transformer is required.

Each grid will be at the same direct current potential as the plate of the preceding tube, so

that direct aperiodic impedance coupling can be utilized in both the radio and audio stages. I

Between the tubes 2 and 3 is a selector circuit or lumped tuning unit comprising a pair of 5 loosely coupled coils 23, each in a series with a variable condenser 24. These condensers are in parallel, having a common ground at 25. The grid of the tube 3 is united to one of the coils 23 and the adjacent condenser 24, the other coil 23 being in series with one of a pair of loosely coupled coils 26, the other of which is in series with the plate of the tube 2. The coils 23, with the coil 26 in series with one thereof, are connected to the conductor l1 as shown. With the tube 2 interposed, antenna reactions are prevented from influencing the tuned selector circuit.

The plates of the tubes 3, l, 5 and 6 may all have suitable impedances in the connections between them and conductor 15. All the plates operate at the same steady potential, eliminating the need of voltage dividers; and only one filament winding I0 is needed for all the tubes. Hence the current needed is small, and the rectifier [2 may be small. The absence of C bias on the grids further simplifies the problem of supplying power to the tubes.

A loud speaker of the static description is illustrated at 21. To provide polarizing voltage, a small two-element vacuum tube rectifier is shown at 28. Across the mains 8 is another transformer primary coil 29, with one secondary 30 connected to the anode of the rectifier 28, and another secondary 3| to energize the oathode thereof. The other terminal of the coil 30 is united to a large resistance 32, in series with a much larger resistance connected to one terminal of the loud speaker. Between this terminal and the plate of the tube 5 is a suitable condenser 34. The other terminal of the loud speaker is of course joined to the negative terminal of the rectifier 28. In parallel with the loud speaker and rectifier 28 is a filter condenser 35. A connection may be placed between the lead to the plate of the tube 5, and a point between the resistances, if desired. These resistances 32 and 33 may have values of 150,000 and 500,000 ohms respectively.

The rectifier 28 will supply approximately 500 volts across the speaker; but, as the condition is a static one, no current at all is required once the condenser 35 is charged. Therefore, the rec tifier and the transformer can be very small. Any type of speaker other than an electrostatic one may be used if preferred.

The receiver as above described is thus constructed around tubes of the external-grid type and affords several important advantages. The simplicity of circuit arrangement is obvious and makes possible the manufacture of a receiver at extremely little expense. Also the arrangement shown utilizes but two radio frequency stages, a detector and two audio frequency stages; and in respect to number of tubes used, is quite comparable to the average broadcast receiver of today.

With regard to the external-grid, considering first the tube itself, it is equal in performance to existent types of screened-grid tubes, but much simpler. It contains in the bulb but two elements, the filament and the plate. Tubes of this type may be manufactured quite as cheaply as incandescent automobile lamps. The gridhas merely the form of a metallic sheath around the outside of the bulb.

Such a tube makes possible the operation of the filament directly from an alternating current source without necessity of resorting to indirectly heated cathodes. This statement holds true of tubes used in all positions of the set.

Comparing this construction with the present type of indirectly heated cathode screen-grid tube, the cost of the external grid-tube is negligible.

Due to the fact that the grid is insulated from the electron stream, the usual grid blocking condenser or transformer coupling may be dispensed with. Examination of the drawing shows, as above stated, all grids to be at the same steady D. C. potential as the plate of the preceding tube, allowing the use of direct impedance coupling in both the radio and the audio stages.

Aside from the question of simplicity and economy the tube itself, for a large output, can be made physically much smaller than previous tubes. In view of the present trend toward small or so called midget sets, the question of size is important. Unquestionably, a receiver constructed according to this invention can, for the same performance, be made much smaller and more cheaply than existing sets.

The detector and all other tubes are impedancecoupled, and the coupling units are simply choke coils which, due to the small current carried, are of Very small dimensions. These choke coils are connected from the plates of the tubes to the conductor [5.

The radio frequency and the audio frequency amplifier tubes are hard tubes; the detector being of the soft variety, but it is to be understood that all of the tubes may be made of the soft or gas filled type with slight changes in the structure of the same design.

What is claimed is:

l. A radio receiver comprising amplifier tubes and a detector tube, each of said tubes comprising an electrically heated cathode a plate and an external grid, means for heating the cathodes of all the tubes and maintaining them at a common potential, including said detector tube, with alternating current, a conductor connecting the plate of some of said tubes directly to the grid of a following tube, and a load impedance between said conductor and a source of direct current for maintaining said plate and said gridv at the same potential and polarity relative to the respective cathodes.

2. A radio receivercomprising radio frequency and audio frequency amplifier tubes and a detector tube, each of said tubes having an internal anode and cathode with anexternal grid, connections for heating and maintaining at a common potential the cathodes of all the tubes including the detector tube with current from an alternating source, a conductor connecting the plate of a radio frequency amplifier tube with the grid of a detector tube, a second conductor connecting the plate of said detector tube to the grid of an audio amplifier tube, a high frequency choke connected between said first conductor and a source of direct current for maintaining the plate and grid con-'- nected thereto at an equal potential, and a low frequency choke connected between said second conductor and said source of direct current for maintaining the plate and grid connected thereto at an equal potential relative to the respective cathodes associated therewith.

3. A radio receiver comprising radio frequency, detector and audio frequency amplifier tubes, each of said tubes comprising a cathode and an anode, with a grid cooperating therewith, the grid of each tube being directly connected to the anode of a preceding tube,. means for maintaining the cathodes of said tubes at a common potential, and means for impressing a direct current potential on said anodes via a choke coil so that the potential of any grid and the anode connected thereto is the same relative to the respective cathodes.

4. A radio receiver having vacuum tubes in cascade, each tube containing an anode and a cathode, with a grid on the exterior of the tube, the plate of one tube being connected with the grid of the next succeeding tube, means for maintaining the cathodes of said tubes at a common potential, and a source of direct current to impress a potential via an impedance on said plate and grid, the potentials on said plate and grid being equal relative to the cathodes associated therewith.

5. A radio receiver having in combination radio frequency amplifier tubes, audio frequency tubes, an intermediate detector tube, each of said tubes including a cathode, means for maintaining said cathodes at a substantially common potenial, a tuning element between the first radio tube and the next succeeding tube, a conductor connecting a plate of one of said radio frequency amplifier tubes to a control grid of the detector tube, a second conductor connecting a plate of the detector tube to a control grid of an audio amplifier tube, a high frequency choke connected between said first conductor and a source of direct current for maintaining the plate and grid connected thereto at an equal potential, and a low frequency choke connected between said second conductor and the source of current for maintaining the plate and grid connected thereto at an equal potential and polarity relative to said cathodes.

6. A radio receiver having vacuum tubes comprising radio frequency and audio frequency amplifiers and. an intermediate detector tube, means for energizing the cathodes and anodes of said tubes from a source of alternating current and maintaining said cathodes at a common potential, said means including a small rectifier, the grids of each tube being exterior to the tubes, means for connecting the grid of one tube to the plate of a preceding tube for maintaining the same at a like potential relative to said common potential, and a choke coil forming a direct aperiodic impedance coupling between an interconnected grid and plate and the output of said rectifier.

'7. A radio receiver comprising vacuum tubes connected in cascade, each of said tubes comprising a filamentary cathode, an anode and a grid, means for commonly energizing and maintaining at a common potential all said cathodes so as to provide a source of free electrons within the tube, the plate of one tube being directly connected to the grid of the following tube, each plate being fed from a source of direct current through a suitable coupling impedance, each interconnected grid and plate being of the same potential and sign with respect to the cathode source.

EARL L. KOCH.

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