GRID CURRENT

Radio Record, Volume I, Issue 27, 20 January 1928, Page 3

GRID CURRENT

A NEW THEORY, éver since the advent of the first transformer coupled valve audio amplifier we have always guarded against the presence of grid current in the grid-filament circuit of the valves. We have been informed that grid current causes amplitude distortion, a change in the signal wave form, a reduction in the valve amplification, in general everything detrimental to good audio aniplification. In fact, all fans have heen warned against permitting grid current in any amplifiers, Now we hear ot w sew system of audio amplification in which grid current is permissible; in which the amount of grid current usually encountered with very detrimental results in a transformer coupled audio system, has no effcct upon the wave form or amplification. This new theory of amplification is propounded by KF. &. Hiler, and pertains to tuned double impedance aniplification, DISTORTION TWLIMINATHD, The presence of grid current is usually considered as an indication of valve overloading, and is made audible in the loudspeaker by a rasping or blasting sound on certain frequencies. With this new system, it seems as if this form of annoyance is removed. The reason for permitting a certain amount of grid current is founded upon the fact that the momentary change iu the grid filament circuit when grid current is present is not reflected back upon the primary circuit of the coupling unit in this system of amplification. Neither is the amplifying operating characteristic of the grid choke altered until the grid filament resistance drops sto a very low value,