US2286996A - Cathode-to-spacer assembly - Google Patents

Description

J v A. B. DlCKlNSON Q ,9 6

CATHODE-TO- SPACER ASSEMBLY Filed April 29, 1941 INVEN TOR.

[AN 3. luck/M90 BY ATTORNEY.

tion, of a radio-tube embodying Patented June 16, 1942 CATHODE-TO-SPACEB ASSEMBLY Allan B. Dickinson,

of Delaware Cedar Grove, N. 1., assignor. to Radio Corporation of America,

a corporation Application April 39, 1941, Serial No. 390,889

an invention relates to radio tubes, particularly to methods and means for rigidly supporting cathode sleeves in such tubes.

In conventional radio receiving tubes where the electrodes are held .at spacers, considerable diiiiculty is caused by loosened cathode sleeves. Although a sleeve may appear to be tight when assembled with its spacer, it often loosens so that it can vibrate after a few hours of use.

An object of my invention is an improved cathode sleeve and spacer. assembly that will not loosen during use.

The characteristic features of my invention are defined in the appended claims and the preferred embodiment thereof is described in the following specification and shown in the accompanying drawing in which- Flgure 1 is an elevational view, partly in seemy novel cathode and spacer assembly.

Figure 2 and Figur 3 my novel cathode and spacer are detailed views of assembly during I two stages of manufacture.

The tube shown in Figure 1 is of conventional construction in so far as the envelope I, enclosing the conventional cerned. The cathode sleeve 8 is exteriorly coated with an electron emissive oxide layer and internally receives an insulated heater wire. Other electrodes, such as the grid 4 and anode '5, are mounted concentric with the cathode and are supported upon side rods engaging at their ends insulating spacers 8 and 1. The spacers are commercial clear mica sheets with the laminae and their. lines of cleavage parallel to the surface of the sheet.

Although the cathode sleeve may be inserted at its ends in holes in the micas and so closely fitted during assembly that the sleeves cannot move, it has been found that after several hours of use the sleeves dom of the sleeve in its hole will permit the sleeve to vibrate and cause microphonic disturbances in the output circuit of the tube. Where the tube is subject-to continual vibration, as in aircraft or motor vehicles, slight vibration of the sleeve rapidly becomes worse, the supporting holes for the sleeve apparently being reamed out by movement of the sleeve until the'holes bcome so large cathode-to-grid shorts may result. It is the mica in contact with the oathode dehydrates at cathode temperature, causing the mica to chip or powder away. Heat will put! and decrepitate the mica, and split and separate probable that their ends in micaelectrode assembly 2, is 0011- will loosen. The slightest free- (cl. ass-21.5)

the thin laminae, the edges of which are easily crumbled to powder.

My novel sleeve and mica assembly eliminates crumbled mica adjacent the cathode. The sleeve 3 is provided withan embossed head 8, which preferably is annular. The bead is' spaced from the end of the sleeve, so that when the sleeve is inserted in its hole, as shown in Figure 2, to

. bring the bead into contact with the rim of the mica holes on one side of the mica, the end of the sleeve will protrude beyond the other side of the mica. With a pair of tweezers or. pliers, opposite sides 8 of the protruding sleeve are pinched to collapse the sides together. The, sides ill of the sleeve, intermediate the pinched side portion 9, are by this operation forced outwardly beyond sleeve. The side portions Ill are fanor wedgeshaped and taper from the bead 8 outwardly to the rim of the sleeve. -As the tapered side portions Ill of the sleeve ride outwardly over the mica - upper rim of the upwardly, forcing the bead 8 into crushing engagement with the lower rim of the mica hole. The mica is hence compressed between the bead and the tapered side portions III of the sleeve, and although the portion of the mica in contact with the sleevemay be dehydrated-by heat, the sheet cannot split, nor its edges fray and crumble.

I have made many thousands of tubes with cathodes according to my invention without detecting any looseness of the sleeve after hundreds of hours of operation of the tubes at normal operat- 8 of my novel cathode-spacer assembly is demonstrated by the fact that-if the bead 8 is spaced from the mica sheet when the end is pinched, so that the sleeve may move lengthwise, the same tubes develop serious microphonics and cathodeto-grid short circuits.

Particularly good results have been obtained in assembling tubes, according to my invention, of the types commercially known as 6K7, 637. GSK'Z, 12SK'Z, 68.17, 128.17, 6C5 and 6.15, having 4 mica spacers .008 to .015 inch in thickness and nickel cathode sleeves .045 inch in diameter.

thickness.

My improved'cathode sleeve and spacer as- 1,

sulating sheet comprising forming a cathode the periphery of the hole, the sleeve is pulled temperatures and voltages. The effectiveness The nickel stock of the sleeve is about .002 inch in sleeve'with an annular embossed bead near one end, inserting said end through a hole in said sheet, and bringing the head into engagement with one side of the sheet at the rim of the hole so that said end protrudes beyond the other side oi the sheet, and then, while said sheet and said bead are in contact, pinching vtogether opposite sides of said protruding end of the sleeve.

2. A radio tube comprising a plurality of electrodes including a cathode sleeve, a mica sheet engaging the ends 01- said electrodes to hold the electrodes in insulated spaced relation, means to secure one end of said sleeve in a hole in said sheet to prevent longitudinal and transverse movement of the sleeve in the hole. said hole being only large enough to receive the sleeve, said comprising ahead on the sleeve oneendotthesleeveandinflrmengag ment with one side oi the sheet, opposite e wall oi'the sleeeve withinthehole outvrsrdlyiromthebeadsothatsaidportions embed in the edges ofsaid hole and tighten said bead against the mica sheet.

3. A radio tube comprising an insulating sheet. an indirectly heated cathode sleeve with its end being flared outwardly to wedge the sheet at the hole against said bead.

ALLAN B. DICKINSON.

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