INSERTING THE TUBES.
Note: —In the panel type receivers, tubes should be inserted before placing receiver in console. Instructions for fitting this type receiver into console are furnished in a separate sheet supplied with the console.
Before inserting the tubes, it is necessary to first remove the large metal shield (plate) which covers the tube sockets and units in the front part of set. To do this, remove the cork stoppers which are inserted in holes in plate (for protection in shipping only), if these have not already been removed by the dealer, then unscrew the knurled brass thumbscrews a few turns to loosen them, slide plate to the right and lift off.
Next remove the cylindrical metal tube shields or covers for the screen- grid tubes. For shipping protection only, these are covered by cardboard tubes. If these cardboard tubes have not yet been removed by the dealer, remove them and then take off the metal tube shields. These shields fit rather tightly, and a little twisting motion may be required to get them off.
Now refer to Figs. 3 and 4, the part which shows location of tube sockets, and study this carefully. Note also that there is an identifying plate located on the chassis near each tube socket indicating the proper type of tube for that socket.
Before attempting to insert any of the tubes, observe carefully the arrangement of the prongs on the tube base, and the corresponding holes in its socket. The five-prong tubes can be inserted most easily by locating the single prong, which is a little separated from the other four, over its corresponding hole before insertion.
The location of the small metal pin in side of tube base should be used as a guide when inserting the four-prong tubes. Our chart shows the direction in which the pin should point, for each four-prong tube. Note that two of the prongs are thick and two thin. Do not try to force the tubes in. They should go in with a moderate pressure. If they do not, check up and see if prongs are being inserted correctly, and pin points in right direction.
The "screen-grid" tubes (type UY-224 or C-324) are the ones which have a small metal terminal on top. These are to be inserted in the sockets at front of set, which contain the bases for the cylindrical metal shields. After inserting these tubes, replace the cylindrical shields over them. These shields, as mentioned above, fit quite tightly on their bases and a little twisting and pressure is required to fit them on tightly. Then fit the thimble contact (attached to flexible lead from condenser) over the small metal cap at top of each of these tubes.
Next insert the detector tube (directly to right of screen-grid tubes), and place over it the large metal cap, furnished with the receiver (in a small brown envelope). Then insert the remaining five-prong tube in its socket. Finally, replace the large flat plate shield over the tubes already inserted, so that the large holes in shield fit over the knurled brass thumb nuts which project slightly above the main chassis assembly. Loosen these nuts a few turns, slide shield to left so that the bolts are within the small extension of large holes in shield. Then screw down knurled nuts firmly with the fingers.
Finally insert the three remaining tubes. BE VERY CAREFUL NOT to insert one of the power tubes (UX-245 or CX-345) in the rectifier tube (UX-280 or CX-380) socket. These tubes are of the same size, but the filament voltage