The Birmingham age-herald., 1922-05-14
FUNCT|ONOF GRID
 IN TUBE SEI S
 FULLYEXP[A|NED
Most Important Element Be- cause It Controls
 Detector and
 AmpIifier

The most important element in the vacuum tube is the grid, and as t vacuum t4be itself is the most impor- tant instrument in a receiving set, the grid naturally assumes major impor- tance in the whole re ;eiving apparat- us. For th,- reason I intend in this weeks article, to describe the func- tion of the grid and the apparatus that Is necessary for use in eonjunc- tien with 1t.
 In tke first place. the grid is to the vacuum tube what the trigger is to the gun. It actually controls the &C., 'tl of the tube and releases t-fe stor- ed-up energ. of the "B" batteries through the operation of the tube. Tn order that this function should operate successfully, it is necessary that the circuit connected to the gr.s should contain a grid condenser and grid leak. The grid condens- CT is the smallls. condenier used in radio work. It can consist of two plates one -qu O inch in area, sep arateG by single fielectrie, giving it a capacity of .o0025 mid.
 No Mystery In Apparatus
 From -he foregoing, it will he seen how simple the grid condenser really Is. There Is nothing n ore mysteri- ous about the grid leak. It Is simply very h,gh resistance shu teG across the condenser itself. This grid leak, for instance can be constructed with an ordinary sos. lead pencil by sim ply making mark uIel a piece of hter and tten connecting a terminal at each end of the mark. The graph ite from the pepci. will form a path way between the two terminals of a very high resistance, the value of which, of course, will depend upon the quality of tfe graphite In the sn- ci1. As an average amount. this re- sistance will be In the neighborhood of | megonfn; ar, in other words 1000, 900 ohms.
 It Is necessary, of course that tIds line be continuous throughout, and in the event of a home ade grid leak of this character. it is possible to ex- pertinent urtil the correc. value of resistance is obtained adding to the thickne or width of the pencil line, until the correct value is attain ed. Of course, correspondingly, If too much Is already on, 1t can be erased, care t'ng taken that 1e con tinuity of the lin' is not disturbed.
 Such is the description of the ap- paratus used in conjunction with the grid. You may quite nat rally ask, Why is the grid leak necessary. es- peciaEy vths n 1t consists Of such sim pie material?' The answer to this question is best given by describing what takes place when the train of waves Is receiN ed on the aerial.
 Grid Has Negative Charge
 The grid in the vacuLs subs is charged to the negative potential. which Is necessary for the successful functfoning of the vacuum tube. Now as each of th,-e wave ]: aims pass over the aerial. and then induce a current In the grid circuit, the grid has an accumulation of negative charges piled upon 1t in rarid success tton and some means must be taken to permit these to leak off.
 Without the grid leak, the oily way In which this ca. be done is through the tube itself, o. over the edges of the condenser. but, of course. In this case the leakage is not rapid enough to return the valve to it's normal operation. The addition of tn s1 i'd Jea,- takes care of this situ- alton and permits these excessive charges to leak off easily and at the same tim. prevent ny accumulation taa would reduce the efficiency of the tube or choke it up.
 O.. course, this grid leak and grid condenses a. only used in connection with the vacuum tube where the tube itself is being operated as q detector of incoming electric oscillations When a yat uum tube s being en- ployed as an anplfier, tube nat urally is performing an entirely diff ferent function, and, Of course. oper- ates in an ,ntirely different amer. Consequently, the grid leak and grid condenser are A~t necessary
 Standard Equipment Ia Trend
 The modern practice in the design of radio receiving equipment IS to produce standard apparatus that will operate at certain average perform ance und every and all conditions. and the consequence is tha. all manu faetured grid leaks are of standard value of resistance. For the experi- menter, however, better results can be obts ned with q racei ing set where all of the parts are aGjustabIe ard this of course applies to the grid leak and the grid condenser It fs