US2400082A

US2400082A - Electronic tube

Info

Publication number: US2400082A
Application number: US445953A
Authority: US
Inventors: William W Eitel; Jack A Mccullough
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1942-06-05
Filing date: 1942-06-05
Publication date: 1946-05-14
Anticipated expiration: 1963-05-14

Description

May 14, 1946. w. w. EITEL ETAL 2,400,032

ELECTRONIC TUBE Filed June 5; 1942 2 Sheetg-Sheet 1 4 INVENTORS WILLIAM w EITEL UACK A. MFCULLOUGH THEIR ATTORNEY y 1946. w. w. EITEL ET AL 2,400,082

ELECTRONIC TUBE Filed June 5; 1942 2 Sheets-Sheet 2 |NvENT6R WILL/AM w. E/TEL LIA K AM; CULLOUGH THEIR ATTORNEY Patented May 14,1946

ELECTRONIC TUBE William W. Eitel, San Bruno, and J aek A.

McCullough, Millbrae, Calif., assignors to Eitel- McCullough, Inc., San Bruno, Callf.,'a corporation of California Application June 5, 1942, Serial No. 445,953 2 Claims. (01. etc-27.5)

Our invention relates to an electronic tube particularly adapted for high frequency work.

It is among the objects of our invention to provide a tube of small physical size, having an improved structure of, arrangement for, and mount ing of the electrodes and leads in the envelope, all designed with due regard for transit time factor, electron migration, inter-electrode capacity,

inductive efiects, and thermionic efliciency.

Another object is to provide a tube structure adapted for facile assembly with maintenance of accurate spacing and alignment of parts.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention, as we may adopt varient embodiments thereof within the scope of the claims.

Referring to the drawings:

Figure 1 is a side elevational view of a tube on approximately double scale, embodying the improvements of our invention; and

Figure 2 is a plan view of the same.

Figure 3 is a vertical sectional view on still larger scale, taken in a plane indicated by line 3-3 of Figure 2.

In terms of broad inclusion, our tube comprises an envelope enclosinga plurality of coaxial electrodes, including a cathode, grid and plate. The several electrodes are supported on leads; the grid lead being disposed coaxially of the electrodes, and the plate lead transversely thereof. In our preferred tube the envelope comprises a pair of cup-shaped sections sealed together along abutting edges. The cathode leads are preferably sealed to the base section, and the grid and plate leads to the body section of the envelope.

In greater detail, and referring to the drawings, our tube comprises a cylindrical envelope of glass or the like having a body section 2 and base section 3, both cup-shaped and sealed together along abutting edges at the bead 4 in a plane lying transversely of the envelope. The base section is shorter than the body; more like a shallow dish compared to the deeper cupped body 2. Base section 3 also preferably has thicker walls than the body to give added strength at the base of the tube. A tubulation for evacuating the envelope is connected to the body section and, after exhaust, is sealed off the pump at point 5. The envelope is of small physical size, say about 1% inches in diameter by about 1% inches in length.

Within the envelope are mounted a plurality of coaxial electrodes, including a plate 6, grid 1 and cathode 8. The plate or anode G is a metallic cylinder, preferably tantalum, supported by a bracket 9 on the inner end of a heavy tungsten lead I I. This lead is disposed transversely of the electrode axis and projects thru the side wall of envelope section 2 at seal [2. Such arrangement provides a short plate lead, desirable for high frequency work.

Bracket 9 is a yoke-shaped strap of tantalum having arms spot welded to the sides of plate Ii. Both parts being of tantalum they weld readily. It is more diflicult to weld to the tungsten however, and we preferably first spot weld a piece of nickel l 3 to the bracket and then weld this to the end of lead II. The body of nickel interposed between the parts alloys or fluxes readily with both the tantalum and tungsten, providing a strong joint.

Grid 1 comprises a plurality of spaced vertical wires, preferably platinum, welded at opposite ends to tantalum rings l4 and reinforced at the center by a wire ring Hi. The lower end of the grid is free, and the upper terminal end is supported on a heavy tungsten lead I1. This lead is arranged coaxially with the electrodes and projects thru the top of envelope section 2 at seal it. The grid supporting means preferably comprises an end cap IQ of tantalum welded to the inner end of leads I! and having its flange welded to grid ring it. The above arrangement provides a short grid lead, desirable for high frequencies.

A nickel disk 2| is preferably interposed between cap it! and the lead to facilitate welding the tantalum to the tungsten. This disk preferably extends outwardly beyond the grid and thereby also functions as a heat radiating fin and as a shield to protect seal l8 against excessive heating. In a small tube of this wind where seal I8 is in line with and fairly close to the electrodes, special precautions must be taken to prevent the seal from cracking under heat. Shield 2| aids in this. As a further protective measure, the grid itself is extended a considerable distance beyond 5 the end of the cathode to thermally isolate the terminal end of the grid from the intense heat zone about the cathode. Because of the small size of the grid wires and their length of path beyond the heat zone, little heat is conducted out to the end of the grid. On the other hand, if the heavy lead I! was carried in close to the heat zone, much heat would be conducted out to the seal.

Cathode leads 22 and 23 are also preferably of tungsten. They project through the base sec- 2 2,4cc,0e2

tion of the envelope at seals 24, Lead 22 is provided with a reduced extension 26 of tungsten bent to extend upwardly through the center 01' the cathode. The other lead 23 projects upwardly to a point adjacent the lower end of the cathode; and may either be a solid rod as shown in Figure l or have a reduced extension 21 as illustrated in Figure 3. The lead extensions are butt welded to the enlarged portions, preferably using nickel 28 as a flux at the welds.

Cathode 8 is preferably of the filamentary type comprising a coil of thoriated tungsten welded at the upper end to lead extension 26 and at the lower end to a tantalum strap 29 which in turn is welded to the other lead.

The tube is fabricated by forming the envelope in two separate sections which, prior to sealing together, are open at one end. Plate lead I I and grid lead I! are sealed in place in body section 2. The plate assembly is then welded to lead ll, after which the grid assembly is welded to lead II. By mounting the plate first it may later be used as a guide for aligning the grid. An alternate procedure is to first weld the electrodes to the leads, apart from the envelope, and then seal the leads to the glass, using a suitable jig to maintain proper spacing and alignment.

The cathode leads are sealed to the separate base section, and filament 8 is welded in place. Since the cathode lead project out through the open mouth of the shallow base section, the filament 8 may be readily positioned and welded in place. After mounting the electrodes the filament is centered within the grid and the two envelope sections are fused together along abutting edges at the bead seal 4.

The tube structure above described permits the use of short heavy leads for the grid and plate, without danger of cracking the glass seals, because the seals are thermally isolated from the electrodes. I late supporting bracket 9 functions as a thermal insulator because tantalum is a poor conductor of heat, and because the wide arms of the yoke-shaped strap provide large radiating surfaces, whereby what little heat is conducted is largely disipated before it reaches lead I I. If the heavy tungsten lead II were brought in close to plate 6, without heat insulating it, a large amount of heat would flow out along the lead and seal l2 would crack.

Another feature deserving special mention is that the use of a nickel flux at the welds produces a clean joint devoid of oxides and other contamination which, if present, would make it diflicult to thoroughly outgas the parts during evacuation of the tubes.

We claim:

1. An electronic tube comprising an envelope embodying a pair of cup-shaped sections sealed together along abutting edges, a plurality of electrodes in the envelope disposed concentrically about the axis of said envelope sections, and means mounting an electrode on one of said sections and another electrode on the other section, the plane along which the envelope sections are sealed together being perpendicular to said axis.

2. An electronic tube comprising an envelope embodying a pair of cup-shaped sections sealed together along abutting edges, a cathode and grid and anode disposed concentrically about the axis of said envelope sections, means including a lead concentric with said axis mounting the grid on one of said sections, means including a lead disposed perpendicular to the axis mounting the anode on the last mentioned section, and means mounting the cathode on the other section, the plane along which the envelope sections are sealed together being perpendicular to said axis WILLIAM W. EITEL. JACK A. McCULLOUGH.