US2337401A - Base construction for electron tubes - Google Patents

Description

Dec. 21, 1943. 5, MILLER 2,337,401

BASE'CONSTRUCTION FOR ELECTRON TUBES Original Filed Feb. 8, 1958 A nie/var UNITED Examin STATES PATENT OFFICE BASE CONSTRUCTION FOR ELECTRON TUBES Carl F. Miller, Corning, N. Y., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts 4 Claims.

Thi invention relates to electron tubes and more especially to base constructions for such tubes.

A principal object of the invention is to provide a radio tube having a series of plug-in contact prongs at its lower end with a central metallic electrostatic shield member located between the prongs to shield electrostatically the major part of the prongs especially that part actually intended to engage in the cooperating contact socket.

A feature of the invention relates to an electron tube having a metal shell base at its lower end provided with a central metallic shield member which is electrically connected by means of a metal strap to the metallic shell and to ground whereby the simple act of plugging the tube into its socket grounds the shell and also one of the contact pins.

A further feature of the invention relates to a base construction for radio tubes which base has a spiderlike metal bottom through which the contact prongs pass and with special grounding means between one of the prongs and the spider, in conjunction with a central tubular metal member which is also electrica ly connected with said spider for shielding certain of said prongs.

A still further feature re at s to the novel o ganization, arrangement and relative location and interconnection of parts wh ch constitute an improved plug-in base construction for electron tubes.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

While the invention is capable of application to any type of radio tube having two or more electrodes in the mount or electrode assembly, it is particularly advantageous in tubes wherein the control grid or signal input electrode is to be totally shielded electrostatically from an anode or output electrode. While therefore, the invention will be disclosed herein as embodied in a radio tube of the pentode type, this is done merely for purposes of explanation and it will be obvious that various novel features can be applied to tubes having a greater or less number of electrodes. Accordingly, in the drawing,

Fig. 1 is a vertical sectional view of a tube of the pentode type embodying the invention.

Fig. 2'is a horizontal sectional view of Fig. 1 taken along the line 2-2 thereof.

Fig. 3 is a horizontal sectional view of Fig. 1 t en along the line 3--3 thereof.

Fig. 4 is a bottom view of Fig. 1.

Fig. 5 is a perspective bottom view of the improved metal base according to the invention.

Referring to the embodiment of Figs. 1 to 4, there is shown an evacuated glass bulb I having its lower end closed by a glas cup base having a substantially fiat disc bottom 2 and a rim 3. Preferably the bottom 2 is of much thicker glass than the wall I of the bulb, and the glass rim 3 preferably tapers in thickness from the bottom 2 to the wall i where it is sealed. The cup 2 and its rim 3 are preferably formed a a unit separate from the bulb I, to which it is later sealed after the electrode assembly or mount has been assembled as described hereinbelow. Preferably the bottom 2 is formed with a series of integral bosses d in the regions where the rigid metal rods 5 to i2, inclusive, are sealed therethrough, and these rods are sealed into member 2 in a vacuum-tight manner as described in detail either in U. S. Patent No. 2,219,574, or in U. S. Patent No. 2,250,183.

As shown, the rods 5 to l2 extend upwardly into the envelope to act as support or current lead-in members for the various electrodes of the mount; these rods also extend downwardly to act as rigid contact prongs whereby the tube when completely finished can be plugged into a suitable contact socket having a series of spring contacts to receive respectively prongs 5 to 12. Preferably, although not necessarily, the bottom 2 is of '705-AJ glass, and the rods 5 to l2 are of a special alloy which is capable of being directly sealed to the glass 2 in a vacuum-tight manner. As examples of such alloy may be mentioned, "Kovar an alloy consisting substantially of Fe, Ni, Co; or Fernico an alloy consisting substantially of Fe, Ni, Co. Preferably the lower ends of prongs 5 to l2, inclusive, are provided with rounded points to facilitate insertion of the tube into a socket.

As hown more clearly in Fig. 2, the contact prongs are arranged in a circle around the center of member 2, and the latter is provided with a central opening l3 which is in communication with the tipped-off exhaust tubulation I4. Supported on the inwardly projecting ends of rods I! and I8, is any well-known form of radio tube mount or electrode assembly Preferably this assembly is of the unitary type, that is with the electrodes assembled as a unit between upper and lower mica discs l5 and I6. An example of a typical unitary mount is found in U. S. Patent No. 2,084,734. The main metal uprights l1, l8, pass through a shallow metal cup is and are welded at their lower ends to the prongs 5 and 9, respectively. Cup i9 is held in place on uprights I! and I8 by means of downwardly projecting struck-out metal tabs which are welded to said uprights. The bottom of member I9 is provided with a longitudinal slot 20 to allow the side rods of the various electrodes as well as the cathode, to extend downwardly without being short-circuited by member l9. The ends of slot 20 are struck-up to form tabs 2| to support the lower mica disc it which is fitted within the rim oi cup l9. Mica I6 is held in place in any suitable manner, for example by swaging the uprights I! and ill or by means of metal lugs or tabs welded to said uprights and bearing against the upper face of disc I6. In the well-known manner disc IB is provided with a series of perforations to receive the lower ends of the various electrode side rods and the cathode.

The drawing shows an electrode assembly of the pentode type comprising a central electronemitting cathode sleeve 22 having an insulated heater filament 23 on its interior, the ends of which are connected respectively to prongs l and 8. The electrode assembly also includes a control grid in the form of a fine wire helically wound around the side rods 24, 25, the side rod 25 being connected at its lower end to prong ill: a shield grid similar to the control grid and w und around the side rods 28. 21, with s de rod 26 connected at its lower end to prong l2; s. suppressor-grid likewise in the form of a line wire helically wound around side rods 28. 29: and a tubular metal plate 30 welded to side rods 3| 32. Side rod 3| extends downwardly through an enlarged opening (not shown) in member I! so as not to be short-circuited therewith, and is welded to prong 5. The lower end of side rod 32 passes through mica II but does not reach member l9. The upper ends of plate side rods 3|, 32. are provided with tabs (not shown) to support the top mica l5 which is similar to mica l6 and is provided with a similar series of side rod and cathode perforations.

It will be noted that the suppressor- grid side rods 28, 29, extend upwardly further than the remaining side rods, and welded to the side rods 28, 29, is a flattened tubular metal strip 34 which bears against the upper face of mica [5 to hold it in place. A short metal tab 35 connects the cathode sleeve 22 to member 34, consequently the suppressor-grid and the cathode meat the same shielding potential.

For the purpose of shielding the electrodes and the contact prongs electrostatically and for preventing undesirable radiation from the electrode system, there is provided an inverted metal cup 35 having a top metal closure 31 with a longitudinal slot 38 in registry with member 34. The ends of slot 38 are provided with struck-up lugs 39 which are welded to the suppressor- grid side rods 28, 29. The shield 36 extends downwardly beyond, but in close fitting engagement with, the rim of member I9 to which it is welded at a plurality of points around its periphery. It should also be noted that member 36 extends downwardly a suiflcient distance to overlap the prongs 5 to i2 inclusive, and to overlap the rim 40 of a metal cup member within which the tube is seat ed. This metal cup member is preferably of the construction disclosed in detail in U. 8. Patent No. 2,238,025, and comprises a. spider-like base 4| having a series of circular openings to receive the glass bosses 4 and the several contact prongs.

In other words the bottom of the cup may be considered as formed of a central hub portion 4| with radially extending spaced arms 4 l which define the openings through which the contact pins pass. The base is held in place on the tube in any well-known manner as for example by a ring of cement 42.

Preferably, the member 4| carries centrally thereof a hollow tubular metal member 45 which performs the double purpose of a protective housing for the glass tubulatlon i4, and a supplemental electrostatic shield between the various contact prongs. Member 45'may be formed with a longitudinal guiding rib or key 45 to facilitate insertion of the tube into its socket and member 45 may also be formed with a circumferential locking groove 41 adapted to engage a suitable grounded contact spring 48 in the contact socket (not shown). Preferably the prong 9 which is connected to members i9, 36 and to the suppressor-grid, and cathode is connected by a strap 49 to the member 4|. In order to complete the electrostatic shielding of the contact prongs, there is provided a metal disc 50 having a central opening 5| in registry with the tubulation opening l3. Member 50 also has a vertical metal extension 52 adapted to enclose the plate prong 6 as shown more clearly in Figs. 1, 2 and 4. Extension 52 is provided with wings 53, 54, which are interposed between the plate prong 6 and the adjacent prongs 5 and 1. Member 52 is electrically connected to the mount shield by means of metal tabs 55 welded to member l9 and member 52.

By the foregoing construction, the entire mount as well as the contact prongs are substantially completely electrically shielded. The mount is substantially entirely enclosed within the members I9, 36 and 31 and the contact prongs are shielded by the member 36, which overlaps the member 40, and by the members 4|, 50 and 52 as well as by the member 45. The arrangement disclosed reduces to the smallest practical extent the separation between the lower end of the mount and the exposed ends of the various contact prongs and even the portion of the contact prongs between the base of the bulb and the mount are substantially entirely shielded. Consequently, the tube is very well adapted to use in high frequency work and with the structure disclosed, interelectrode capacitances lower than 0.004 mid. have been obtained. Thus it is possible to construct a tube of the shield grid, pentode or similar type with all the connections at the lower end of the a tube and avoiding the usual flexible lead for connecting the control grid in circuit. If desired, the bulb portion of the envelope may be provided with a peripheral bead 55. While Fig. 1 shows a shield for the plate prong, it will be obvious that a plurality of shields similiar to member 52 may be carried by disc 50 each shield enclosing an appropriate one of the prongs.

This application is a division of application Serial No. 392,605, filed May 9, 1941. (Patent No. 2,289,588) which in turn is a division of application Serial No. 189,295, filed February 8, 1938, issued as U. S. Patent No. 2,250,184.

What I claim is:

1. In an electron tube, the combination of a disc of insulating material having a plurality of connection pins extending from one face of said disc and spaced from the center of said disc, a cylindrical metal shell connected to said base and extending above the other face of said disc around the periphery thereof, said shell having an openwork bottom consisting of a central hub portion with radially extending arm portions connected to the shell, said radially extending portions defining apertures through which said pins pass, one of said pins being directly connected to one of said arm portions by a short metal strap.

2. In an electron tube, the combination of a base comprising a disc of insulating material having a plurality of connection pins extending from one face of said disc and spaced from the center of said disc, a cylindrical metal shell connected to said base and extending from the other face of said disc around the periphery thereof, said shell having an open-work bottom consisting of a central hub portion with radially extending arm portions connected to the shell, said arm portions extending along a face of said disc, said hub portion being provided with a central aperture, electrostatic shielding means comprising a portion in alignment with said aperture and extending downwardly from one face of said disc between said pins and parallel thereto for substantially their entire external length, said shielding means comprising another portion extending upwardly from said other face of said disc for a substantial distance within said shell, one of said pins extending through said bottom and in electrical contact with the arm portions thereof.

3. In combination, a radio tube bulb enclosing an electrode assembly, a base for said bulb comprising a cylindrical metal shell having an openwork bottom, a plurality of rigid plug-in pins passing through said bottom, a depending tubular metal pin-shielding member concentrically mounted with respect to said bottom and extending downwardly therefrom to at least the outer extremities of said pins, and a metal strap directly and electrically connecting said pin-shielding member and said cylindrical metal shell to one of said pins.

4. A supporting and plug-in type base for a radio tube comprising a cylindrical metal shell having an open-work bottom consisting of a central hub with radially extending arm portions connected to the shell, said hub portion being centrally perforated and carrying a hollow tubular metal plug-in and pin-shielding member centrally dependent therefrom.

CARL F. MIILER.

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