Radio broadcast .. (1922-30)

904 Radio Broadcast which should be wide enough to project to about the edge of the coil whereas the strip inside the coil will be only f inch wide. ASSEMBLY THE assembling may then be started by placing lugs on all instrument binding posts and mounting the parts themselves upon the panel following the scheme of Fig. 4. No wiring should be attempted before the b uilder has first studied the lay-out carefully and has turned the lugs in the directions which will permit of the shortest possible connecting wires. After this has been done, the variable condenser, coupler, and rheostats should be removed from the panel and the filament wires put in. These wires should be run along the panel at a point about two inches above a line passing through the socket bases. Small lengths of bus bar should be soldered to the main lines and carried down to the lugs on the sockets. It is advisable to cover this wiring with spaghetti. The antenna coil which has been previously wound should now be placed between two thin strips of bakelite about % inch wide and 3! inches long. In the end of each of these bakelite strips a No. 1 8 hole should be drilled, placed 3-^inches between centers and arranged so that when one strip is placed over the other the holes at either end will coincide. If i £ inch round head -£% machine screws are put through these mounting strips at each end with a nut on the far side of the second strip, it will be possible to clamp the coil between the strips which rest on the winding at a point directly above one of the lengths of adhesive tape. It will be noticed on the condenser that there are two holes used for small mounting screws on the back plate which are approximately on a line which would run through the rear shaft bearing. These screws should be removed, and after a second nut is placed on each of the ij inch screws running through the coil mounting strips, these two new screws should be inserted in the holes in the condenser from which the original ones were removed. They may then be tightened up, care being taken to keep the nuts loose upon them until they have been entered at least 5 inch into the condenser end supports. One nut on each screw may then be tightened up against the condenser end plate, and the second nut on each screw tightened up in the opposite direction against the bakelite strip. This will leave the coil clamped firmly between the two bakelite strips and mounted on the back of the condenser. In connecting this coil to the condenser, the end near the tap should go to the frame of the condenser if it is of the grounded rotor type and the end farthest from the tap should go to the statoi plates, which will in turn go to the grid of the r. f. tube. The tap itself leads to the antenna binding post. It is very much simpler to purchase the coupler completely built up than to endeavor to build it, since its construction will involve the turning out of a special shaft, bearings and lock washers. For this reason it will not be taken up, although the winding data has previously been given, and if the constructor feels confident of his ability to build it, he will have sufficient knowledge to supply the mechanical coupling arrangement details suitable for his needs. The r. f. condenser with its coil is then mounted at the left end of the panel and the detector condenser placed in the next position to the right, followed by the coupling unit which is located between the detector and first audio tube. The rheostat is also put in position and wired with one of its terminals to the positive A battery binding post and the other to the line connecting the positive filament terminals of all sockets. The balance of the set wiring presents no particularly difficult features and if care is used, a very neat job can be made of it. The stator plates of both condensers should be connected to the grid sides of their respective circuits. TESTING THE SET AFTER the wiring and assembly has been completed, the set is ready for test. If 20 1 -A tubes are used, a 6volt storage battery will be required and a go-volt B battery tapped at either 22 or 45 volts for the detector. A 4^-volt C battery will also be required for the audio amplifier. If vv-igg tubes are used, the B battery will remain the same, but the A battery should consist of three dry cells connected in series or if extra life is desired, six dry cells connected in series parallel. The batteries should be connected to the set, and as they are connected no sparking should be noticed. If sparking is noticed it indicates that there is a short circuit in the wiring, which should then be very carefully checked. After the batteries are connected, a single tube should be inserted in the right hand socket and the rheostat just barely turned on. If the phone plug is inserted in the right hand jack a click should be heard and if a finger is placed on the grid terminal of this last tube either a click or squeal should result. If this