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In the R. B. Lab.
307
FIG. 7 The "works" of Mr. Brown's one tube reflex set.
Note the spider-web coils
you have or can obtain, always, of course, confining yourself to good apparatus. Mr. Brown uses an Acme transformer; this laboratory has used the Amertran and Pacent with equally good results. If a set calls for a straight coil of wire, but you have (or prefer) a honeycomb, bank-winding, or spider-web, use it. The chances are it will work as well as, or even better than the inductance specified.
A radio set is of infinitely more value and pride to the owner, when it is, in part at least, a tribute to his own originality and thought.
TRANSFORMERS AND REFLEX SETS
WITH the stir that reflex sets are making in radio circles, a word as to the proper series connections between radio and audio-frequency transformers is quite appropriate, and will, perhaps, clear up some of the difficulties under which many of our readers seem to be laboring.
There are, of course, certain ends of both radio and audio transformer windings which should connect to the grid and plate, with the remaining terminals of the secondary and primary going respectively to the filament and plus (positive) side of the B battery. In the majority of cases, these terminals will be found
marked as "G," "F," "P" and the plus sign,-f-, or in another equally obvious manner. However, in a few cases, the reader may be left in doubt. In the case of a single-layer primary and single-layer secondary radio transformer, such as is found in the neutrodyne circuit, the coils are always wound in the same direction. Then if the start of the primary is led to the plate, the start of the secondary must run to the grid. In the case of audio transformers, the outside leads from primary and secondary run to the plate and grid respectively. It is generally a simple matter to determine the outside leads by noting how far from the core they enter the windings. In reflex sets the grid terminals and the plate terminals must always run to those two elements of the tube, either directly or through the windings of another transformer. The windings must always be "pointed" or heading in the right direction. For instance, the grid connection from an R. F. transformer will go to the grid, as it should, while the filament end of the secondary winding will run to the grid connection of the audio transformer. Thus the filament connection of the R. F. transformer finally reaches the filament, after running through the secondary of the audio transformer, while the grid connection of this latter transformer reaches the grid by running through the secondary of the radio transformer.
The circuit shown in Fig. 8 (the Inverse Duplex as improved by Mr. Eric Shalkhauser), indicates this principle very clearly by the lettering at the transformer terminals.
LOADING THE TWIN VARIOMETER SET
By WM. H. WEST
SINCE the new allocation of wavelengths, the majority of owners of the twin variometer type of apparatus have experienced difficulty in receiving stations transmitting on waves above four hundred meters. The September, 1923, GRID section of RADIO BROAD