US2157719A - Thermionic microphone - Google Patents

Description

May 9, 1939.

F PULASKI 2,157,719

THERMIONIO'MICROPHONE Filed Sept 15, 1956 3nveutor Emil/6' L F 9 uZws'ifi;

(Ittonleg May 9, 1939 UNITED STATES PATENT OFFICE THEBMIONIC MICROPHONE Frank L. Pulaski, Sherwood, Oreg.

Application September 15, 1936, Serial No. 100,810

2 Claims.

My invention relates to microphones. More particularly, my invention relates to a thermionic tube which is actuated by a diaphragm to thereby vary electronic currents within the tube in accordance with movements of the tube.

I am aware that microphones have been used which depend upon the movement of a voice coil within a magnetic field. The moving coil, cutting magnetic lines of force, establishescurrents which vary in proportion to the movements of the coil. In the present invention a magnetic field is utilized for establishing relative movements of electrodes within a themionic tube. In the preferred arrangement the thermionic tube moves with the diaphragm to which it is attached. The magnetic field restrains the movement of a pair of shielding electrodes, thereby variably exposing the cathode of the tube to the influence of the anode.

My invention may be best understood by reference to the accompanying drawing in which Fig. 1 is a view, partly in section, of one embodiment of my invention,

Fig. 2 is a front elevational view of the apparatus illustrated in Fig. 1,

Figs. 3 and 4 are sectional views, partly in elevation of one type of thermionic tube which may be employed in my invention,

Fig. 5 is a plan view of the centering spider which is mounted within the tube, and

Fig. 6 is a schematic circuit diagram illustrating the connection of the thermionic tube.

Throughout the specification and drawing, similar reference numerals will be used to indicate similar parts.

Referring to Fig. 1, a diaphragm supportinghousing I is attached to a U-shape permanent magnet 3. The housing may include suitable orifices 2 which permit -unrestricted movements of the diaphragm. The larger end of the diaphragm supporting member terminates in a ring 5 on which is mounted a conical diaphragm l. corrugations 9 are included between the ring 5 and the diaphragm 'I to provide flexibility. At the apex of the conical diaphragm is suitably secured a thermionic tube H which will be hereinafter described in detail. A pair of spiders B3 are mounted in spaced relation with the vacuum' tube II. The spiders are connected at their centers by a rod l5. The spiders l3 are constructed of a suitable spring material of a form which is. by way of example, illustrated in Fig. 5. The circumferences of each of the spiders are secured to the inner surface of the envelope. A magnetic armature I1 is fixed to the rod IS in a.

position opposite the pole pieces ill of the U- shape magnet. The tube is mounted so that it will just clear the pole pieces l9 of the permanent magnet 3.

Referring to Figs. 3 and 4, the thermionic tube 5 H is comprised of a glass, or non-ferrous metal, evacuated envelope 2i. Within the envelope are mounted an anode 23 and a cathode 25 which is heated in the conventional manner. A pair of end plates 21 are mounted on opposite sides of the 10 cathode 25. The rod i5, which is fastened to the centers of the spiders i3, is extended to within the anode 23. The extended portion of the rod includes a yoke 29. A pair of shielding electrodes 3| are mounted on the ends of the yoke. The 15 shielding electrodes and the end plates are preferably so constructed and arranged that the cathode is substantially completely shielded from the anode when the tube is normally disposed within the pole pieces.

A schematic circuit diagram, Fig. 6, illustrates one circuit arrangement which may be employed. The anode 23 is connected through an output transformer 33 and anode battery 35 to the oathode 25. The end plates 21 and shielding electrodes 3| may be connected together and biased slightly negative with respect to the cathode 25 by a battery 31 or the like. The leads are made flexible to permit free movements of the tube.

Having described the elements of my invention, the theory of operation will now be given. As the diaphragm is actuated, the magnetic field between the pole pieces i9 and the armature ll restrains movements of the armature but permits the tube, as a whole. to move. Such movement will cause the envelope including the anode, end plates, and cathode to move but the armature I1 and shielding electrodes will be restrained from movement. Thus the cathode is exposed to the influence of the anode. m

Since the anode may be biased positively with respect to the cathode, it will follow that electrons emitted from the cathode travel to the anode. The number of electrons will be regulated by the variable shielding eilect of the shielding electrodes. Thus, as the diaphragm I is actuated, the thermionic tube II will move to and fro, carrying with it the anode, cathode and end plates, while the shielding electrodes will be maintained in the same position as their normal arrangement. In this manner the shielding electrodes permit varying currents to fiow between the cathode and the anode in proportion to the tube movements.

It should be understood that numerous modia suitable electromagnet.

flcations within the scope or my invention may be made by those skilled in the art. For example, the permanent magnet may be replaced by It should likewise be understood that the shielding electrodes may be made of diiferent shapes and of difierent arrangements. A suitable spider, secured between the free end of the thermionic tube and the magnet 3, may be used to position the tube and to add -restoring force to the diaphragm. Although I have illustrated a conical diaphragm, it should be understood that numerous diaphragm arrangements may be used. I contemplate that the novel arrangement of thermionic tube and restraining field may be used in combination with actuating mechanism other than a diaphragm. It should be understood that these modications and others are within the scope and spirit of my invention which is only limited in accordance with the foregoing specification and appended claims.

I claim as my invention:

1. In a device of the character described, a diaphragm, a thermionic tube including envelope, anode and cathode electrodes mounted within and in fixed relation to said envelope, shielding electrodes flexibly mounted within said envelope, means for causing said anode and cathode electrodes to move in response to movements of said diaphragm, and means for restraining the movement of said shielding electrodes, said means ineluding a magnet fixedly mounted external to said tube and having its lines of force passing through said tube in a region remote from said electrodes, an armature flexibly mounted within said envelope and located in the field of said magnet, and means operably connecting said armature and said shielding'electrodes so'that said magnet restrains the motion of said armature and ot said shielding electrodes.

2. In a device oi the character described, a diaphragm, a thermionic tube including an envelope, anode and cathode electrodes mounted within and in fixed relation to said envelope, shielding electrodes flexibly mounted within said envelope and positioned so as to partially block electrons flowing from said cathode to said anode; means for causing said anode and cathode electrodes to move in response to movements of said diaphragm, means for restraining the movement of said shielding electrodes, said means including a magnet having opposing pole pieces fixedly mounted external to said tube and having its line oi! force passing through said envelope FRANK L. PULASKI.

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