SILICON CRYSTAL RECTIFIERS 13 



Development or the Shielded Rectifier Structure 



Rectifiers of the ceramic cartridge design, though manufactured in very 

 large quantities and widely and successfully used in military apparatus, 

 have certain well recognized limitations. For example, they may be ac- 

 cidentally damaged by discharge of static electricity through the small 

 point contact in the course of routine handhng. If one terminal of the 

 unit is held in the hand and the other terminal grounded, any charge which 

 may have accumulated will be discharged through the small contact. 

 Since such static charges result in potential differences of several thousand 

 volts it is understandable that the unit might suffer damage from the dis- 

 charge. Although damage from this cause may be avoided by following 

 a few simple precautions in handling, the fact that such precautions are 

 needed constitutes a disadvantage of the design. 



Certain manufacturing difficulties are also associated with the use of 

 the threaded insulator. The problem of thread fit requires constant 

 attention. Lack of squareness at the end of the ceramic cyhnder or lack 

 of concentricity in the threaded hole tends to cause an undesirable eccen- 

 tricity or angularity in the assembled unit which can be minimized only by 

 rigid inspection of parts and of final assemblies. At the higher frequencies 

 (10,000 megacycles), uniformity in electrical properties, notably the radio 

 frequency impedance, requires exceedingly close control of the internal 

 mechanical dimensions. In the cartridge structure where the terminal 

 connections are separated by a ceramic insulating member, the additive 

 variations of the component parts make close dimensional control inherently 

 difficult. 



To eliminate these difficulties the shielded structure, shown in Fig. 6, 

 was developed. In this design the rectifier terminates a small coaxial 

 line. The central conductor of the line, forming one terminal of the rec- 

 tifier, is molded into an insulating cylinder of silica-filled bakelite, and 

 has spot welded to it a 0.002-inch diameter tungsten wire spring of an 

 offset C design. The free end of the spring is cone shaped. The rectifying 

 element is soldered to a small brass disk. Both the disk, holding the 

 rectifying element, and the bakelite cylinder, holding the point, are force- 

 fits in the sleeve which forms the outer conductor of the rectifier. By 

 locating the bakelite cylinder within the sleeve so that the free end of the 

 central conductor is recessed in the sleeve, the unit is effectively protected 

 from accidental static damage as long as the holder or socket into which 

 the unit fits is so designed that the sleeve establishes electrical contact with 

 the equipment at ground potential before the central conductor. The 

 sleeve also shields the rectifying contact from effects of stray radiation. 



The radio frequency impedance of the shielded unit can be varied within 

 certain limits by modifying the diameter of the central conductor. For 



