The "Free Grid One"

Radio Record, Volume II, Issue 24, 28 December 1928, Page 28

The "Free Grid One"

Claimed to Eliminate Distortion

(By

Free

Grid

— IN your issue of November 30, I notice the usual complaint re distortion from 2YA. Presuming that this is due to broadening of modulated wave, naturally distortion follows when received on receivers which have the inherent fault of broad tuning to powerful signals. During September, whei 2YA. was so terrible that radio column editors ahd correspondents waxed exceedingly wroth, I was listening to practically 100 per cent. distortion-free programmes night after night. The sacret is the "Kree Grid" cireuit de-

seribed in "Popular Wireless" of June 23. This circuit allows maximum regeneration to be used without over loading detector and therefore gives a sharpness of tuning otherwise unobtainable with strong signals on regenerative set. Further, as it is a form of anode rectification, the tone is perfect at the detector, it reduces HT consumption and gives smooth reaction control. Its faiilt is that it reduces volume a bit

on 4 very efficient regenerative set, although my authority says the coritrary, Any leaky grid regenerative can be altered easily and inexpensively and the details are as follow :-

Changing to the Free Grid Circuit. REMOVE filament end of secondary coil from valve socket terminal, insert a .001 or .0015 fixed condenser between coil end and filament negative terminal on valve socket, take out grid leak, short grid condenser and the alteration is complete. It may be found an advantage to increase Det B Voltage, "Popular Wire-

less" stating that this voltage may sometimes be increased as high as 100 volts without causing overlap in reaction. My own set will not take more than the usual voltage.

The Free Grid is said to work equally well with magnetic (movable tickler), Reinartz or throttle control regeneration. The filament end of this latter however must be taken to A-++ and this necessi-

tates fitting a leak holder if leak had previously been placed across grid condenser, The .001 in filament end .ofeoil is not shorted or removed..: iy ' Its presence in circuit when changi pack to leaky grjd does not affect the set if alteration has been made _ to wiring of grid leak, and further, i. will be noticed that it serves as 4a hocking condenser to keep Plate HT out of ‘filament should reaction condenser become accidéntally shorted. Claims Made.

(HERE is one point: to remember and that is that all stations will have to be relogged, the Free Grid making a consideravie difference in condenser readings. For listeners residing in YA cities and desiring practically perfect reproduction, the Free Grid will give it provided their audio stages and spedker are what they should be. Short-wave enthusiasts whose sets have that terrible affuction "threshold howling," will find the Free Grid silent and smooth ‘in action, although volume Wwili probably suffer more so than or the broadcast band. Readers are advised to leave grid condenser and Jeak holder in position, as they can revert to the old method. at any time by simply removing the short on condenser and replacing leak. ee a ee ee a a ae ee ae oe an > ) Pye