Grid-Bias Batteries

Radio Record, Volume III, Issue 16, 1 November 1929, Page 30

Grid-Bias Batteries

Probable Cause of Distortion Moke distortion is produced by rundown grid bias batteries than is suspected, and with the introduction of the screen-grid valve, more eare-should be taken to maintain the specified grid voltage. The popular method nowadays is to build this battery into the set, and. once it has been adjusted to supply the proper potential to the grids of the audio valves, it is apt to receive no further attention for some little time. Despite the fact that it is not ealled upon to supply any current to the set, the grid battery's life is defi--nitely limited. . Minute Jeakages take place between its sockets, particularly if the surface is allowed to become dust-covered. Apart from this, the moisture within the cells slowly evaporates, thus reducing their activity. Thus there is a continual small decline in the D.M.F. of a grid battery, and, as the voltage drops, inereasing distortion .results. These batteries should be renewed regularly every six months or so, and the noticeable improvements in reproduc: tion more than compensates for the small outlay.