Radio age (Jan 1927-Jan 1928)

RADIO AGE for January, 1927 The Magazine of the Hour 19 and 135, should be assured. If using a B eliminator, test your voltages to see the proper values are secured. In using dry batteries be sure to use the heavy duty type, since the receiver when using a power tube, takes from 30 to 50 milliamperes. In actual operation and with everything going full blast our test set ran 35 milliamperes. Inside of the 111A coils there will be found small rotors. These rotors govern the pickup from the antenna, and the pickup from the oscillator. It would be a good idea for the set builder to experiment with different inductive relationships of these rotors. The rotor in the antenna coupler should be varied until a good signal strength is secured with a given length of antenna, while the oscillator rotor may also be varied until the best results are secured. Tune in a local station first and get the set adjusted for best wave transmission which might ordinarily be heard on the super, is likewise done away with. In the audio end with the falling characteristic of these transformers many of the shrill whistles heard on another set are cut off to a point where they are not noticeable. In the lower register we found tones from the well known "oompah" of the Sousaphone, the throbbing cello and a number of the pedal notes of an organ that we did not believe were in existence before. One of our radio wags suggested the audio transformers used in this receiver should be sold to a great many of the broadcasting stations for line transformers. In another portion of this story we will give the results of our tests. At present we will confine ourselves to a description of the circuit, section by section. The Description FIGURE 1 of the blueprints shows the front view of the panel, which is 7 by 21. On it are located the jack for the meter, volume control, selector one, RF gain control, selector two, filament control, and the filament switch. The drawing gives the detailed dimensions. In the second blueprint, Figure 2, are shown, reading from left to right, the three intermediate stages, the shielded first detector, the shielded oscillator, and the two stages of audio with output transformer. The stage shields are available so that any one can duplicate this feature of the design. Figure 3 shows the under side of the subpanel on which a majority of the connections are made, most of these connections being run together across the bottom of the subpanel. Schematically the Clough superheterodyne is shown in Figure 4, which is the diagram from which the set should be studied and wired. All markings are shown on the diagram so that even a novice should not hesitate to make up a set. Referring to the schematic circuit, we will dissect it for our readers. The first detector circuit is located inside the stage shield. It comprises the coil socket, 515, the plug-in coil, 111-A, the tube socket 511, the variable condenser 316, the grid condenser and grid leak. Ground is common with the stage shield, the negative filament terminal 4 of the coil, the rotor of the variable condenser, the rotor of the midget condenser (.000025 mfd) and one side of the bypass capacity which is across the 45 volt lead. The oscillator circuit is likewise shielded with a stage shield, which is common with the negative connection of the potentiometer, the negative of the filament. A strap is shown below the ground connection which serves to join the two stage shields and place them at ground potential, thus limiting Photograph of the completed Clough superheterodyne with the stage shields removed from the first detector and oscillator