Page:Popular Science Monthly Volume 88.djvu/971

 Popular Science Monthly

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��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

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