US2151781A - Electron discharge tube - Google Patents

Description

Patented Mar. 28, 1939 PATENT OFFlCE ELECTRON DISCHARGE TUBE Nils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Original application April 14, 1932, Serial No. 605,274. Divided and this application May 14,

1936, Serial No. 79,648

1 Claim.

This invention relates to a novel electron discharge tube for use in ultra high radio frequency signalling.

In tubes used hereinbefore to relay or amplify ultra high frequency oscillations, numerous difiiculties have been encountered due to the internal capacity coupling between the several electrodes enclosed in the envelope. of the tube, also due to the impossibility of providing low impedance leads from the tube elements in conventional tube design. This inter-electrode capacity is the cause of many undesirable effects. The use of a tube in which the inter-electrode capacity is present, even when compensated, is attendant with many serious disadvantages.

Many schemes have been devised to counteract or compensate the effect of this internal capacity. In some arrangement, neutralizing capacities are placed at appropriate points external to the tube envelope and between the desired electrodes directly or throughout the interconnecting circuits to compensate or to counteract the effect of the inter-electrode capacity. While it is true that these neutralizing capacities were to some extent effective to counteract the internal capacity or to negative the eiiect of the internal capacity between electrodes and to de-couple the input and output circuits, they are not entirely satisfactory at very high frequencies since the neutralizing capacities themselves, together with sufficient amounts of inductance, which is inherent and thus unavoidable, form new paths in which free oscillations can develop at some other, sometimes only slightly different, frequency. Thus, for very high frequencies, neutralizing, or rather balancing, can only be accomplished for one particular frequency at the time. As there is nothing to. prevent the circuits from choosing these free oscillations, they provide a serious problem which offsets the advantages gained by the use of neutralizing capacities. Furthermore, these neutralizing capacities are usually added as directly as it is possible (outside the tube envelope) to the internal capacity between the electrodes in the tube and thereby contribute to a decrease in the maximum frequency, which can otherwise be relayed or amplified by the thermionic tube and its associated circuits. This decrease being due to increased total capacity with resulting lower capacitive reactance which holds down the voltage swing of the electrodes.

In other cases, tubes of the screen grid type were used. It was found that even these tubes and their associated circuits became very unstable in operation where ultra high frequencies were to be relayed or amplified, because of the difiiculty of providing a low inductance, low capacity lead from the screen to ground.

All of the above disadvantages are obviated in accordance with the present invention by the use of a novel thermionic tube wherein the envelope comprises two vitreous portions separated by a metallic ring having an extending flange, the ring being connected with the gridelectrode which is disposed somewhere near the median line of the ring and of the envelope. The anode electrode is disposed in one of the vitreous bulbs of the tube, and the heatedcathode is disposed in the other vitreous bulb of the tube.

By the use of the novel tube, as described above, in a push-pull circuit in which the grid electrode is maintained at a constant potential and the oathode electrode is swung or oscillated at ultra high frequency with respect to the grid electrode, extremely stable and satisfactory operation may be obtained. Furthermore, the use of such arrangement permits higher frequencies to be relayed or amplified than has been heretofore possible.

Stable operation of thermionic relays and amplifiers, at frequencies where conventional neutralizing methods are successful, is also obtained in accordance with the disclosure set forth in my United States application #605,274 filed April 14, 1932, of which this application is a division, by the use of a tube of the type heretofore known in the art, or by the use of a tube constructed in accordance with the present invention in a new and improved circuit in which the elements of the circuit are so arranged that the circuits balance themselves without the use of neutralizing capacities or equivalent oscillation suppressing or preventing means.

The novel features of the thermionic tube have been pointed out with particularity in the claim appended hereto.

The nature of the tube and of the use of the same in circuit arrangements, will be clear to the reader from the following detailed specification, and therefrom when read in connection with the attached drawing, throughout which like reference characters indicate like parts, and in which:

Figures 1 and 1a show practical embodiments of my novel thermionic tube; while Figure 2 shows, for purposes of illustration, an ultra high frequency relay circuit in which a pair of tubes, as illustrated in Figures 1 or 1a, are incorporated.

Referring to Figure 1, T indicates a thermionic tube having vitreous portions l and 2 which are closed at the ends 3 and 4 by re-entrant portions 5 and 6 respectively. The open ends I and 8 of the vitreous portions land 2 are sealed in shallow channels on opposite faces of annular metallic ring member ID shown in the drawing as a substantially flat washer or disc with a central opening smaller in diameter than and concentric with the wall of the envelope. The peripheral portion I2 of metallic member I0 is provided with bolt holes I4 therein as shown in Figure 1, or a. threaded periphery, as shown in Figure 1a.

The outer ring-shaped portion i 2 permits mounting of the tube T. The grid electrode I8 of thermionic tube T is suspended within the opening in the ring member ID. The specific nature of this grid forms no part of the present invention and need not be discussed in detail here. The grid, however, may be of any known shape or structure. The cathode or filament electrode l8 is supported in the re-entrant portion 5 of the bulb I while the anode electrode 20 is supported in the re-entrant portion 6 of the member 2. It will be obvious that if the ring I2 is mounted in an opening in a metallic sheet or support 22.

by bolts as in Figure 1 or by threads as in Figure 1 and in any manner as shown in Figure 2, the electrode l8 may be electrostatically isolated from the. electrode 2!] to a very high degree by. means of the grid 16 and ring l2. Further, the

resistance of the grid lead-in conductor or ring I 2 between the electrode and the external connection is reduced to a minimum because of its substantially fiat washer-like shape. Ultra-high frequency currents, which my improved tube is designed to generate and amplify, flow only on the surface of the ring, and the impedance to the flow is approximately proportional to the length of the conducting path along the surface of the ring.

The length of the path between the inner and.

outer peripheries of the annular lead-in conductor or ring is a minimum and the impedance between the peripheries is a minimum when the conductor is substantially flat. Ring member I2 is substantially flat and is provided on either face with shallow channels for receiving the ends I and 8 of the vitreous portions of the envelope.

In Figure 2 I have shown a symmetrical relay circuit which includes two thermionic tubes T and T, each constructed as illustrated in Figures 1.

and 1a. Each of these tubes is fixed by its ring I2 to a metal partition member 22 dividing the metal shielding closure member or box 24 into two separate portions. The cathode l8 of T and cathode ll of T are heated from any alternating current source through transformers 26 and 26', each having a symmetrical secondary winding, the outer terminals of which are connected to the cathodes I8 and [8' respectively, and the electrical midpoints 25 and 27 of which are connected to the terminals of an input circuit 30 comprising variable capacity C and inductance I. The input circuit 30 is tuned to the frequency of the incoming signal by means of the inductance I and the capacity C. The incoming signal, which may be derived from any source of ultra high frequency oscillations, is impressed on the inductance I by means of the inductance 2| coupled thereto. Biasing potential to maintain the cathodes l8 and I8" at the desired operating potential relative to grid electrodes l6 and Hi is provided by connecting the midpoint of inductance I through a lead 23 to a source of biasing potential BP having one terminal grounded as shown. The anodes 20 and 20' of the thermionic tubes T and T are connected as shown in a tank circuit TC comprising a tuning capacity C: and inductance I0. Oscillations appearing in the tank circuit TC are conveyedto any work circuit by means of an inductance 32 inductively coupled to inductance 3!. Charging potential for the anodes 20 and 28' is provided by a lead 3| connected on the one hand with the midpoint of the inductance 30 and on the other hand to the positive terminal of a source 34 having its negative terminal connected to ground. In order to prevent any radio frequencies appearing in the input circuit 38 from being introduced into the source of alternating current used to heat the cathodes l8 and 18', the leads 2! and 21 are connected at a point between pairs of radio frequency shunting condensers II and I3 and I8 and II respectively connected in parallel with the secondary windingof transformers 26 and 28'.

In operation, the high frequency oscillations are impressed from the source through winding 2| to the input circuit 30 of the thermionic tubes T, T. The grids of these tubes are maintained at a constant potential lower than the potential of the cathodes. The grids may be at ground potential. The cathodes l8 and I8 of the tubes oscillate at the fundamental frequency of the ultra high frequencies to be relayed with respect to the grid electrodes. The oscillating potentials at the frequency to be relayed appearing on the anodes 20 and 28' are set up in the tank circuit TC from which they are led by means of inductance 32 to any work circuit.

It has been found that by maintaining the grids at an alternating current potential lower than the potential of the cathode, or by grounding the grid electrode as to alternating current potentials, extremely stable operation is obtained. It has further been found that by mounting the tubes, as shown in Figure 2, not only are the an odes and cathodes of the tubes shielded from each other to a high degree, but the output and input circuits of the relay system are electrically separated.

The arrangement of Figure 2 may be used as a frequency multiplier. If the arrangement of Figure 2 is used as frequency multipliers the anodes of the tubes may be connected in parallel or pushpush relation. The arrangement for frequency multiplication in other respects may be as shown in the drawing.

I claim:

An electron discharge device comprising a cathode and an anode, a sealed envelope enclosing the electrodes comprising two cylindrical envelope portions of insulating material, a lead-in conductor of minimum impedance to high frequency currents between connections inside and outside said envelope comprising a substantially flat metal disc with a central aperture of less diameter than the inside diameter of the envelope, the rims of the cylindrical envelope portions being sealed to opposite faces of the disc intermediate the edge of said central aperture and the periphery of the disc, and a grid-like electrode interposed between said cathode and anode and attached to said disc.

N'ILS E. LINDENBLAD.

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