Radio broadcast .. (1922-30)

902 Radio Broadcast unnecessary to neutralize the set. The quality of reproduction was all that could be desired, either with storage battery or dry cell tubes and the difference in volume be tween 199'$ and 2Oi-A's was only about 10 per cent., the sensitivity remaining substantially the same. See Fig. 3. The tuning inductances used in the set are very efficient. I believe they have about the lowest losses of any coils at present used for broadcast reception. They are supported entirely on air with the exception of the two bakelite strips which are approximately | .inch wide. The turns are held in place by means of five strips of adhesive tape which introduce practically no additional losses. Some tests were run off using the coils with and without a bakelite supporting tube and it was found that the sensitivity to weak signals using the air core coils was decidedly superior to that obtained when coils wound upon a bakelite tube were used. The coils are so located that a minimum of loss from surrounding material is introduced. Some question might arise in the mind of the reader when it is seen that one of the audio transformers is very close to the second detector grid circuit coil, but the losses introduced here are negligible, however. This would not be the case if the transformer were located at one of the open ends of the coil. The entire assembly of the set is on a 7 x 24 bakelite panel. No sub-base is used. All parts are screwed directly to the panel itself which is extremely substantial and simple. At the left end of the panel is the r. f. tuning condenser which tunes the grid circuit of the r. f. amplifier. Next is the detector tuning condenser controlling the grid circuit of the detector tube. These two controls function in exactly the same manner as the first two controls on a neutrodyne receiver and may be logged in exactly the same fashion. The third control, or tickler, is what accounts for the extreme sensitivity of the set as it provides a means of varying the amount of regeneration used in the detector circuit. THE PARTS REQUIRED HPHE material used by the author to con1 struct the set is as follows: 2 .0005 low loss condensers (Silver, Cardwell, or Duplex) i Low Loss coupler i Low Loss Antenna coil 4 Hoosick Falls panel mounting sockets. 1 Howard 6§ Ohm rheostat 2 Thordarson 35:1 Transformers i Carter IO2-A Jack i Carter 101 Jack i On-Off Switch i .00025 Mica condenser with leak clips i .002 Mica condenser i .0075 Mica condenser i 2-Megohm grid leak 6 Insulated top binding posts 3 4" moulded dials i 7 x 24 x iV' bakelite panel I 5" length J" brass tubing, spaghetti, lugs, bus bar, solder, etc. Tools: Screw driver, pliers, soldering iron and hand drill with drills and counter-sink. I f the builder wishes, he may substitute other parts than those specified in the construction of the receiver, bearing in mind that they must be of as good quality as those specified and of approximately the same size and values. FIG. 3 The schematic circuit diagram. The various coil terminals are numbered for ease in indentification of wiring. Direct reference may be made to the numbers in this plan and those in Fig. 4