The Value of the Grid Leak

Radio Record, Volume II, Issue 36, 22 March 1929, Page 30

The Value of the Grid Leak

Variation Advisable N tracking down distortion, the small inoffensive looking grid leak is often overlooked, but an incorrect value of this is quite frequently at the bottom of much trouble. Fundamentally, the problem of the grid leak is that a high resistance increases signal : strength, but also increases distortion while the converse is true of the lower value grid leak. The value of this may vary from time to time according to the volume of the station that is to be tuned in. Optimum results, therefore, can be obtained then only by varying very frequently the value of the grid leak. This would necessitate the keeping on hand of a very large number of these resistances which would mean an outlay greater than the average constructor would be prepared to meet. By the introduction of a grid leak clarostat or a variable grid leak with a range of .1 to 10 megohms, adjustment of the value of the grid leak may be made for every condition. At the same time, the inclusion of a variable grid leak acts as a good volume control. On the Low Frequency Side. APART from the detector, the grid leak has an important function to serve in resistance and impedance coupling. By means of an adjustable resistance, the value can be calculated to a nicety and make possible the employment of larger coupling condensers. The substitution will allow of the desired bass notes to be faithfully reproduced. Resistance coupling responds to low frequencies very faithfully, with the result that there is sometimes set up a low frequency oscillation due to coupling between circuits. This is heard in the speaker like the sound of the exhaust of a motor boat. Consequently the term "motor boating" has been applied. The simplest way to offset motor boating when it occurs is to use a lower resistance of grid leak for one or more stages together with smaller blocking condensers. Often the lowering of the grid leak resistance in the first or second stage will serve the purpose. In this respect the variable grid leak will serve the simple cure.