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A Good Four-Tube Receiver
903
FIG. 4
A picture layout of the wiring. The parts are in relatively the same postion as shown in Fig. 2
Before starting with the assembly and immediately after the purchase of parts, they should be carefully checked and inspected to see that they are in first class condition. All bolts, screws, and springs should be tightened up so that no trouble will be encountered further on in assembling the set.
The panel should be laid out with a scriber and square following the diagram given in Fig. 5 if material as specified in the parts list is used.
After all holes have been located they should be drilled and counter-sunk where necessary. If desired, the panel may then be given a sanded finish by rubbing in one direction only with fine sand paper and oil until all traces of the original polish have disappeared.
DETAILS OF CONSTRUCTION
IF THE builder decides to wind the coils used in the set, the simplest method of doing it is to wind them upon a bottle approximately 3 to 3!" in diameter and then break the bottle away from the coil. The method of doing so is to place five strips of adhesive tape lengthwise along the bottle, these strips being held down by two rubber bands at either, end, the sticky sides up. Sixty turns of No. 20 double cotton-covered wire should be wound in place for the antenna coil with a tap taken at the fifteenth turn, the rubber bands may be removed and the ends of the adhesive tape, each strip of which should be approximately 6 inches long, may now be bound back over the coils to hold the turns in place. This will leave five bands of tape, each one running around both inside and outside of the coil
and touching each turn on the inside and on the outside of the winding.
The stator coil of the vario-coupler is wound in exactly the same manner except that at one end of the tube fifteen turns of No. 30 d. c. c. wire are first wound on the bottle and then sixty turns of No. 20 wire put on over this. These fifteen turns are wound single layer, as close together as possible, and the 60 turn winding of No. 20 d. c. c. is put on starting directly over the first turn of the No. 30. When fifteen turns of the stator-secondary winding have been put in place, a tap is taken as on the antenna coil and 45 more turns then put in place. The tickler consists of a small bakelite tube approximately 2 inches in diameter and i inch long arranged so that it may be rotated at the end of the last coil made which is the farthest from the tap. The tickler should consist of between fifteen and twenty turns of No. 30 d. c. c. wire.
A more satisfactory way of supporting the coils would be to paint them with a good grade of insulating dope. I n order to keep the losses low, however, an extra good grade of dope should be used. If the coils are made in this manner, 55 turns in the grid windings will be sufficient, instead of 60 turns, as the insulating compound increases the distributed capacity slightly.
For the vario-coupler two strips of bakelite may be used to clamp the stator coil together and they may project somewhat at one end. These two projecting ends may have a hole drilled through them which will accommodate a shaft to which the tickler coil is attached. Terminals may be machine screws run through one of the pieces of bakelite .strip