Page:Popular Mechanics 1928 01.pdf/130

 of the coils. It was found that in the common practice of testing coils at only one wavelength of the broadcasting band, two or more coils might be perfectly matched at the wavelength at which they were tested, and yet, at some other wavelength, would be hopelessly out of tune. By testing the coils at both the upper and lower ends of the band, the coils so matched would be in close agreement over the entire band, therefore these coils are supplied in matched sets, tested at both 250 and 500 meters. The condensers used are constructed in such a way that they can be assembled in the receiver and either a long control shaft, or insulated, flexible couplings substituted for the regular shafts without disturbing the accuracy of the units. Small neutralizing or balancing condensers, made by the same manufacturer are very useful for equalizing the units of the multiple-tuning condenser, and may be fastened directly to the socket binding posts or to the condensers, simplifying the wiring connections. The audio stages consist of two heavy-type a.f. transformers, together with a power tube, making possible beautifully rounded reproduction of the bass notes. Drilled and engraved panels are available; however, for those who wish to drill their own, full-size drilling templates of the diagrams appearing on page 129 have been prepared.



The wiring diagram on page 126 shows the simple arrangement of the instruments with the coil bases and sockets marked for position. Note, in the photo on page 129, that the subpanel is cut away at front to make room for the rheostat-switch and the potentiometer. Mount the instruments on the front panel first, as shown in the photos on this page. The brackets are then screwed to the underside of the subpanel, and the subpanel assembly completed. No. 14 round, tinned-copper busbar wire is used for wiring throughout the set. It will be noted that the last coil at the right, mounted close to the front panel, has a hinged primary which allows a very close adjustment of the coupling for aerials of various electrical characteristics, and different selectivity requirements. In each case, the No. 6 terminal of the coils is mounted as close as possi-