US2030931A - Electron coupled thermionic oscillator - Google Patents

Description

Feb. 18,- 1936;. w PARKER 2,030,931

ELECTRON COUPLED THERMIONIC OSCILLATOR Filed April 26, 1934 ELE .1.

INVENTOR H2191 W Parker ATTORNEY Patented Feb. 18, 1936 UNITED STATES OFFICE ELECTRON COUPLED THERMIONIC OSCILLATOR Canada Application April 26, 1934, Serial No. 722,451

8 Claims.

' My invention pertains to electron discharge devices especially of the type known as thermionic tubes, and relates more particularly to that type of thermionic tubes employing a plurality of electrode sections within a unitary envelope.

I A type of multi-electrode section tube known as an electron coupled oscillator is now in general use. This tube is essentially the well known screen grid detector-amplifier provided with a 10 triode oscillator section comprising, the cathode of the tube, a control grid and an anode which cooperate to produce a virtual cathode for the tube as a whole having an intermittent electron emission, the frequency of such emission being governed by the frequency of oscillation of the triode oscillator section. Such tubes find a definite place in the art as they replace two tubes, that is, the oscillator and the first detector-amplifier of superheterodyne receiver sets and permit such sets to be economically made in the commonly known midget and automobile sizes.

Receiver set makers have had considerable trouble with the behavior of such tubes .as they stopped oscillating at times for no apparent reason, and are subject to squalling or zule oscillations at high line voltages. I have conducted extensive experiments with such tubes and have made the discovery that their eccentric behavior is due to two causes; first, secondary emission of electrons from the screen grid immediately adjacent the triode section which fiow under the potential gradient of the triode section anode potential to the triode section anode create an internal variable resistance between the screen grid and the triode section anode. The value of this variable resistance is sufiiciently low to constitute a shunt on the inductance connected to the oscillator anode and 40 thus cause the oscillator to stop oscillating. Second, the influence of the screen grid voltage upon the transconductance of the triode section anode is due to an unequal sharing of the space current by these electrodes. In other words, the screen 45 grid diverts electrons and deprives the triode section or oscillator anode of its share of the electron stream which should be constant if constancy of the oscillator is to be achieved.

One of the principal objects of my invention 50 comprises producing an electron coupled thermionic oscillator in which all of these above noted undesirable features are eliminated.

Another object comprises producing an electron coupled oscillator in which the oscillations set up in the oscillator section are stable and do not set up zule oscillations at high line frequencies.

A further object comprises producing an electron coupled oscillator in which the oscillator section is not only highly efiicient at low frequencies l but at ultra high frequencies and is therefore well adapted to function efiiciently under the wide frequency spectrum embracing both the broadcast and short wave bands.

A still further object contemplated by my invention comprises producing an electron coupled oscillator in which the Wave form has a steep wave front of the square wave type and. large amplitude and narrow width whereby the tube may be efficiently utilized as a frequency doubler, tripler, or quadrupler.

I accomplish all of the above desirable results by a novel construction in which the triode or oscillator section of the tube comprises a control grid disposed externally with respect to the oathode and the anode and formed, with reentrant or constricted portions between the cathode and anode whereby both the anode and the cathode are partially encircled by the control grid. Such structure is disclosed and described in my copending application Ser. No. 718,963, filed April 4, 1934.

In tubes which I have constructed in accordance with my invention, I have found that the substitution of my novel triode section in lieu of the triode section now used in such electron coupled, oscillators produces an electron coupled oscillator which eliminates the above. noted undesirable features and attains all of the above noted desirable features.

In the figures accompanying and forming a part of this specification and in which like reference numerals designate corresponding parts throughout: v

Fig. 1 is a broken elevation of my complete improved tube with the grid electrodes'and work anode partially broken away for purposes of clarity;

Fig. 2 is a top view of the same with the enclosing envelope omitted; and

Fig. 3 is a section taken on the line 3-3 of Fig. 1 with the enclosing envelope omitted.

Referring now to the figures, the envelope 2, which is preferably constructed of glass or other vitreous material is provided with the usual press and stem as shown and the usual base 3 containing the contact prongs 4, 5, 6, I, 8, 9, and Ill. The envelope and base 3 are preferably provided with a metal coating 24 sprayed thereon as described in my co-pending application Ser. No. 646,970,

filed December 13, 1932, for a purpose which will hereinafter be discussed.

The press within the envelope 2 supports a cathode 9, the terminals of the heater 3| of which are connected to contact prongs 6 and 8, while the cathode active surface is connected through conductor 32 with contact prong 4. The cathode may be as shown of the indirect heater type or it may be of the filamentary type either coated or uncoated. Adjacent the cathode are rod-like anodes l8 and 2!! electrically interconnected by means of a conductor and connected as shown to contact prong l of base 3. These anodes are supported by spacers 2| and 22 which are preferably constructed of any well known ceramic adapted to withstand high temperatures. The spacers 2| and 22 are supported by means of standards supported by the press and which in turn support the work or output anode l3. The control grid I! for the triode or oscillator section surrounds the cathode l9 and the anode rods l8 and 20 and is formed as shown in Fig. 3 with reentrant or constricted portions whereby the anode rods and the cathode are each partially surrounded by the grid. A screen grid l6 is'provided immediately adjacent the control grid I! and encloses such grid. An additional grid I5 encloses grid l6 and a further screen grid I4 is provided between the work or output anode Hi and the grid l5. Grid I5 is provided with a terminal I and connected thereto by means of conductor 2. This grid functions as the logarithmic control grid of the detector-amplifier section of the tube, and the grid lead I2 is shielded by the metallic mesh collar screen 33 positioned as shown and carried by the standards supporting grid 14. The grids on either side of control grid l5 are, as shown, electrically interconnected.

.All of these electrodes are, as shown, maintained in their relative positions with respect to each other by means of the ceramic spacers 2| and 22. The interconnected grids l4 and I6 are connected as shown to contact prong .9 in base 3, while the control grid of the triode section of the tube is connected to contact prong 5. The output or work anode l3 is as shown connected to contact prong In. There is provided a further spacer 23 which may be of mica for the purpose of positioning the upper portion of the entireelectrode assembly in the envelope 2. This spacer is as shown in Fig. 2 provided with a central aperture to remove the material of the spacer from contact with the supporting standards of grids l5, l6, l1, cathode l9 and the anode rods l8 and 20 to prevent deterioration of the mica spacer by the high temperature carried by these electrodes during the construction and operation of the tube.

The control grid ll of the triode section of the tube as shown in .Fig. 3 is positioned externally with respect to the anode rods 18 and 20 and the cathode 9. The control grid may be constructed on a mandrel and is formed with reentrant or constricted portions as shown in Fig. 3 in order that the grid when in position partially encircles each of the anode rods and the cathode. With such structure of the triode section of the tube any shunting of the oscillator anode inductance is eliminated because the secondary electrons from grid I6 are repelled to grid lB-and do not .flow toward the anode rods l8 and '20 as these are now enclosed by the grid 1 and the potential gradient of grid H. is sufiiciently negative to repel the electrons to grid Hi. This eliminates one of the defective features of such tubes in that it prevents the shunting of the oscillator anode inductance which hitherto has caused the oscillator to stop oscillating. Further, because the anode rods are within the control grid of the triode section, there is a more even division of space current between grid l6 and grid l1 and the electron stream passing to the anode rods l8 and 20 is rendered substantially constant, thus eliminating another cause of cessation of oscillations.

The various electrodes comprising the detectoramplifier section of the tube are the same as those in the commonly known electron coupled oscillator and their functions are well known. It is therefore deemed unnecessary to further explain their uses here.

The construction above described produces an electron coupled oscillator which by experiment has been found to have a high transconductance triode or oscillator section, an oscillator which is stable and does not set up squalling or zule frequencies at high line voltages, and one which is veryefficient at both low frequencies and ultra high frequencies; also, an oscillator in which the wave form in the anode circuit has a steep wave front of the square wave type and large amplitude with narrow width producing a tube which may be used as a highly efficient frequency doubler, tripler or quadrupler.

Experiments have shown that the tube should be preferably provided with the metallic coating 24 which may be maintained at ground or cathode potential for the purpose of eliminating grid action of wall charges and in order to prevent stray field charges from affecting the fluctuation components of the anode currents.

Having thus completely described one embodiment of my invention, what I claim .as new and desire to secure by United States Letters Patent is as follows:

1. An electron coupled thermionic oscillator comprising, a substantially evacuated envelope containing a cathode, a plurality of electrodes cooperating with said cathode and constituting a detector-amplifier section, and a plurality of electrodes cooperating with said cathode and constituting an oscillator section, said'oscillator section including a control grid and anode, said anode being in the form of a plurality of rods electrically interconnected and said control grid being externally disposed with relation to both said cathode and said anode and .formed with reentrant portions located between said cathode and anode.

2. An electron coupled thermionic oscillator comprising, a substantially evacuated envelope containing a cathode, a plurality of electrodes cooperating with said cathode and constituting a detector-amplifier section, and a plurality of electrodes cooperating with said cathode and constituting an oscillator section, said oscillator section including a control grid and anode, said anode being in the form of a plurality of metallic rods electrically interconnected and said control grid being externally disposed with relation to both said anode rods and cathode and formed to have constricted portions between said cathode and anode rods whereby said cathode and each of said anode rods are partially encircled by'said grid.

3. An electron coupled thermionic oscillator comprising, a substantially evacuated envelope containing a cathode, a plurality of electrodes cooperating with said cathode and constituting a detector-amplifier section, and a plurality of electrodes cooperating with said cathode and constituting an oscillator section, said oscillator section including a mesh grid and an anode, said mesh grid being externally disposed relative to both said cathode and anode and formed to have constricted portions between said cathode and anode whereby said cathode and anode are each partially encircled by said grid and a metallic coating on the outer coating of said envelope and adapted to coact with the electrodes within said envelope.

4. An electron coupled thermionic oscillator comprising, a substantially evacuated envelope containing a cathode, a plurality of electrodes cooperating with said cathode and constituting a detector-amplifier section, and a plurality of electrodes cooperating with said cathode and constituting an oscillator section, said oscillator section including a helical grid and an anode, said helical grid being externally disposed relative to both said cathode and anode and formed with reentrant portions located between said cathode and anode and a metallic coating on the external surface of said envelope for coaction with the electrodes within said envelope.

5. An electron coupled thermionic oscillator comprising, a substantially evacuated envelope containing a. plurality of electrodes including an output anode and a triode section for cooperation with said plurality of electrodes and output anode and comprising a cathode, anode and a grid in the form of spaced conductors, said grid being positioned externally to said triode anode and cathode and being formed with constricted portions between said triode anode and cathode.

6. An electron coupled thermionic oscillator comprising, a substantially evacuated envelope containing a cathode, a plurality of electrodes cooperating with said cathode and constituting a detector-amplifier section and. a further plurality of electrodes cooperating with said cathode and constituting an oscillator section, said oscillator section including a grid and an anode, in the form of a rod, said grid being helically and externally disposed with relation to both said cathode and anode and formed with reentrant portions located between said cathode and anode whereby said cathode and anode are separately partially enclosed by said grid.

7. An electron coupled thermionic oscillator comprising, a substantially evacuated envelope containing a cathode, a plurality of electrodes cooperating with said cathode and constituting a detector-amplifier section and a further plurality of electrodes cooperating with said cathode and constituting an oscillator section, said oscillator section including a grid in the form of spaced conductors, and an anode, said grid being externally positioned with relation to both said cathode and anode and formed with reentrant portions located between said cathode and anode whereby said cathode and anode are each partially enclosed by said grid.

8. An electron coupled thermionic oscillator comprising, a substantially evacuated envelope containing a cathode, a logarithmic control grid, an output anode and a plurality of screen electrodes constituting a detector-amplifier section and a secondgrid and anode positioned for cooperating with said cathode and said detectoramplifier section and constituting a triode section, said second grid being helically and externally disposed with relation to both said cathode and the triode section anode and formed with reentrant portions located between said cathode and the triode section anode.

HENRY W. PARKER.

Images