Radio broadcast .. (1922-30)

906 Radio Broadcast Another method of neutralizing the set would be to tune-in a fairly strong signal and then remove the first r. f. tube from its socket. A piece of paper should be placed over one of the filament pins and the tube replaced in its socket. Then, with the tube unlit, the signal will come through weakly and the brass tube should be slid along until the signal does not come through at all or at best with very poor intensity. The receiver having been neutralized, there is nothing more to do, and in tuning it may either be operated with the tickler set at zero and the first two dials handled in the same manner as when tuning a neutrodyne, or the tickler coupling may be increased until the detector oscillates and a signal located by rotating the detector condenser until a whistle is heard. The detector condenser should be left set on the whistle and the r. f. condenser moved to a point where the whistle is strongest. If the tickler coupling is then reduced to just below the oscillating point and the two condensers readjusted very slightly, the signal will be heard with maximum intensity. De Forest ov-3 tubes, which have the same characteristics of 199'$ may be used and will work in very nicely as they have standard bases and do not require adapters. wo-i2's will also work in very well as they also have standard bases. It is probable that the neutralizing adjustment will not be at all critical if 199*5 or wo-i2's are used. TROUBLE SHOOTING THERE is very little that can go wrong with the receiver or that might cause failure to function, and if it is assembled properly, there is no reason why it should not work. However, it is possible gradually to improve it slightly by following some of the suggestions outlined below: Selectivity: If the detector tuning condenser is broad, it indicates the use of an insufficient amount of tickler coupling. It should be possible to make this control very selective indeed by bringing the tickler up to just below the oscillating point. If the r. f. tuning condenser is broad, this may be overcome by inserting a small fixed condenser, say .00025 or .0005 mfd. in series with the antenna which will, in effect, reduce the resistance of this circuit and sharpen its tuning very much. This will not be necessary except with a very long antenna, say over 125 feet. Volume: If the detector can be made to oscillate and the receiver to tune sharply, poor volume may be attributed to trouble in the audio frequency amplifier and should be looked for in this section. Improper connections or misplaced C battery, would account for this. Individual location conditions will more probably be to blame, however. Hand Capacity Effect: This will not be experienced if the stator plates of the condensers are connected to the grid sides of the circuit and if all by-pass condensers are wired in. The by-pass condensers are very important. The .002 mfd. by-pass condenser is quite important and should be connected from the plate terminal of the first audio transformer to either minus or plus side of the filament line. Squealing: This would be due either to too high a value of tickler coupling, failure to neutralize the r. f. amplifier, or more probably to the audio amplifier. If in the audio amplifier, it may be overcome by reversing the leads to the primary of the audio transformers or shunting the secondary of the audio transformers with a .00025 mfd. condenser or \ megohm grid leak, or both. Noise: Noise in the set should be traced by first disconnecting the antenna. If it disappears it is picked up on the antenna and probably cannot be eliminated. If it persists, the first r. f. tube should be removed and so on down the line until it stops. If it stops upon the removal of some tube other than the last one, the noise is probably in its circuit. If it persists throughout the entire set it is due to some faulty common wiring, such as B battery, or A battery, rheostat, or socket contact. Grid Leaks: A 2-megohm grid leak will be satisfactory for practically all tubes used, although it may be found that a 3 or 5megohm grid leak will give a little better result on weak signals. Tickler: The detector circuit should not oscillate until the tickler has been advanced to about 50 to 70 degrees on its dial. If it oscillates at some point below this, turns should be removed from the tickler coil until the oscillation point is brought within this range, if the builder wishes to do so, although this is not very important. If the detector fails to oscillate, reversing the tickler connections will correct matters. Neutralizing: If the r. f. stage cannot be neutralized so that it does not oscillate, the leads to the primary of the r. f. transformer should be reversed. If this fails to correct matters, one or two turns should be removed from the primary, although this would be an extreme case.