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6o
Radio Broadcast
tube was lighted. Then adjust the neutralizing condenser until the signal almost, or perhaps actually disappears. This tube is then completely neutralized and the same process may be applied to the next tube. As each tube is neutralized, the filament prong insulation is removed.
With the condensers and coils used, as described, the amplifier will cover a wavelength range varying from 230 to 600 meters for the entire broadcast band.
WHAT TO EXPECT FROM THE AMPLIFIER
THE author does not attempt to set a distance limit on reception of a set using this amplifier when connected to a detector circuit. The radio public has educated itself to the point where it takes with a grain of salt the highly imaginative claims of sometimes over-enthusiastic set designers about the distance range of their receivers.
It is not our desire to put a limit on the reception qualities of this amplifier. Rather let us say that it will equal any two stage radio-frequency amplifier we have ever tested
650
0 10 20 30 40 50 60 70 80 90 100 Ci CONDENSER SCALE
FIG. 12
A wavelength chart which may be used as an aid in locating stations
Radio Broadcast Photograph A DETAILED VIEW OF THE NEUTRALIZER Part of this condenser is cut away. The turning of the screw, top center, varies the capacity
NEUTRALIZING THE AMPLIFIER
ON THE lower wavelengths it will be observed that the amplifier will go into oscillation more easily than on the higher wavelengths.
Now, by turning the adjusting screw of the neutralizing condenser, up and down, a point may be reached where the self oscillation is entirely eliminated or perhaps only feebly present. This oscillation is recognized in the form of a squeal whose pitch varies. The detailed method of neutralization was fully described in "Notes on the Robert Circuit," in the January, 1925, Radio Broadcast.
It is well to apply the neutralization process at several wavelengths, noting the position of the tubing for each change, so that an average may be struck. If the amplifier works properly, no great difference in the several neutralizer settings will be noted.
Since this circuit, is not reflected it is quite satisfactory to employ the standard neutrodyne method of neutralization. Briefly explained, that is as follows: A station is tuned-in, preferably a distant one, so that the signal is not as loud as a local. Then the first tube is removed from the socket, and one filament prong is covered with a slip of paper or spaghetti tubing, so as to insulate it when replaced in the socket. Now after inserting in the socket (the filament will not light) the station previously tuned-in may be heard faintly. Carefully retune for maximum signal strength, which will not be as loud as when the