Radio Broadcast (Nov 1926-Apr 1927)

42 RADIO BROADCAST NOVEMBER, i9a6 Cam--* Cam Bush'g Screw Switch Blade' %6 EH. Machine Screws ■ _ %2 Section Removed FIG. 9 There are two forms of the Marco illuminated dial on the market. If you have obtained any but the latest models, a slight alteration will have to be made. This alteration, which involves the removal of a section of the frame, is explained elsewhere, and is clearly shown in the above diagram THE CORRECT TUBES TO USE THREE 201-A tubes may be used in the first three sockets and a 171 tube in the last audio socket. At 135 volts of B battery, this latter tube requires about 27 volts of C battery. Now pull out the filament switch. This should light all the tubes. Turn the regeneration condenser so that its movable plates are completely meshed with the stationary plates. Then, with the aid of the tuning chart shown in Fig. 1, set the right-hand dial at an approximate setting for the station it is desired to receive, and slowly turn the knob of the detector condenser, swinging it a few degrees above and below the number on the other condenser. If the station is broadcasting, a regeneration squeal will be heard in the phones or loud speaker. Back off the regeneration condenser setting to diminish the squeal. Then slowly rotate the antenna tuning condenser. If the squeal changes in pitch, the neutralizing condenser should be adjusted until there is no such variation of the squeal pitch. The set is then properly neutralized and may be operated like any other receiver that employs the squeal — V r:-;;^iyT*T»'Ti'>i'j'Ti'*f 3j BINDING POST TERMINAL STRIP All Holes No. 18 2VZ — No. 18 / Holes \kjjH CLAMP FOR 22 k VOLT "C" BATTERY All holes No. 18 < h"2" -X BASE BOARD-PANEL BRACKETS 2 REQUIRED 3% •j w CLAMP FOR 4 h VOLT'C'BATTERY FIG. 10 a . 20 -11 Material For Baseboard 1-pc. ^Jxll}s"x20" 2-pcs.7,6 x Ui"x Uii" Baseboard \, 20" Cleat Cleat Cleat FIG. I 1 For the base board it is essential that good wood be employed, thus obviating any possibility of warping. The base board of the "Lab" Receiver is exceptionally wide, and cleats are employed to strengthen it. The base board supports the front panel rather than the front panel supporting the base board, which is generally the case ened to the base board by means of the brackets, details of which are shown in Fig. 10. To complete the wiring of the receiver the units on the panel are wired to their correct points on the base board. By means of a five-wire fused Belden battery cable, the batteries, with the exception of the two C batteries, may be connected to their respective binding posts. The five wires of the Belden cable are colored as follows; red, maroon, yellow, black with red tracer, and black with yellow tracer. These wires are connected to the binding post terminal strip as shown in Fig. 6. The C batteries, since they are contained inside the receiver cabinet, are connected directly to their respective binding posts, as is also shown in the same diagram. Radio Broadcast Photograph INSPECTING THE JOB Right to left, are Willis K. Wing, editor, Keith Henney, Director of the Laboratory, and Howard E. Rhodes of the Technical Staff. Mr. Henney is pointing to the cabled leads which are distributed along the rear and side of the base board method of tuning. The fact that a squeal can be heard in the loud speaker does not necessarily mean that other neighboring receivers will also pick up this squeal — providing that first you have satisfied yourself as to the proper neutralization of the receiver. This enables you to turn up the regeneration control and then vary the tuning of the detector condenser until the carrier wave of a station is picked up. Now, from this point onwards, it is only a matter of bringing the antenna condenser setting up to the point where the loudest squeal results and then backing off the regeneration control until the squeal is eliminated. In its place ought to be the music, or speech from the broadcasting station to which the set is tuned.