Popular Science Monthly 



943 



Unit Type of Plate Gap 



ANEW type of unit quenched spark- 

 gap is shown in the illustration, 

 which is taken from 191 5 patent No. 

 1,163,568 issued to F. G. Simpson. 

 This gap is of the plate type, but differs 

 from the ordinary plate quenched gap 

 in that damaged sections may be 

 removed without deranging any of the 

 rest of the apparatus. Each unit 

 contains a pair of sparking surfaces, one 

 of which is formed by the upper side of 

 plate 3 and the other by the lower face 

 of 15. These opposing surfaces are 

 machined to be perfectly plane and 

 parallel, and are mounted by the use of 

 the clamping members 5 and 18. The 

 two plates are kept apart mechanically 

 and electrically by the insulating piece 

 12. The details of mechanical construc- 

 tion are clear from the diagram; it 

 should be noted that the spacing of the 

 gap depends upon the distance that 3 

 is screwed into 5, and not directly upon 

 the thickness of the insulating separator. 

 Stops 24 and 26 are provided to keep 

 air spaces between adjacent pairs of 

 plates, and with the flanges 6 in the 

 outer metal piece, aid in keeping the 

 gap cool. The required number of 

 sections, such as illustrated, are grouped 

 to form a complete gap, and connection 

 from the inner plate of one unit to the 

 outer of the next is made through the 

 strip 22. 



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The mechanical construction of a quenched 

 gap unit of the plate type 



Preventing the Audion from Choking 



MANY operators have noticed when 

 they are using the audion detector 

 that there is a tendency for the grid to 

 charge too rapidly and "paralyze" the 

 bulb. In times of severe static this 

 effect may be very annoying, since when 

 the paralysis sets in, all signals stop. 

 It is possible to discharge the grid, and 

 thus to place the detector in operation 



again, merely by placing the fingers 

 across the small stopping condenser in 

 the grid circuit; sometimes, even, the 

 bulb will automatically regain its sensi- 

 tiveness in a second or two after charg- 

 ing. Occasionally, however, there are 

 found very high vacuum tubes which 



This special audion circuit overcomes the 



tendency of the grid to charge too rapidly 



and paralyze the bulb 



will not free themselves of this paralyz- 

 ing charge. If atmospherics are strong 

 and frequent it is sometimes impossible 

 to read a single word without interrup- 

 tion. 



One remedy for the paralysis is to 

 shunt the small grid condenser by a 

 very high resistance, which permits the 

 charge to leak off and so prevents all 

 but the strongest impulses from affect- 

 ing reception. This scheme is used a 

 great deal, but at times is not entirely 

 satisfactory for the reason that when 

 the charging surges are intense, it is 

 necessary to reduce the shunting 

 resistance to so low a value that the 

 sensitiveness of the audion is spoiled. 

 In U. S. patent No. 1,127,371, issued 

 during 1915 to G. W. Pierce, there is 

 shown a new way to do away with the 

 interruptions due to charging. The 

 drawing shows the invention, which is 

 based upon the observ^ation that when 

 the audion is paralyzed the "B battery" 

 current in the telephone circuit is 

 reduced practically to zero. 



Referring to the diagram, the antenna 

 20 is seen to lead to ground 21 through 

 the primary 22 of a receiving trans- 

 former. The secondary of this instru- 

 ment 23, is shunted by the tuning 

 condenser 24, and the terminals carried 

 to the audion grid 13 through condenser 

 25 and to the filament 14 in the usual 

 manner. Battery 18, acting through 

 variable resistance 17, is used to light 



