Radio broadcast .. (1922-30)

Operating the Neutrodyne Receiver Directions for Tuning, How Best to Use Different Kinds of Tubes, and How to "Shoot Trouble" By KIMBALL HOUTON STARK Chief Engineer, F. A. D. Andrea, Inc. This is the third and final article of this series on building the five-tube Hazeltine-circuit receiver. The first two articles appeared in RADIO BROADCAST for December, 1923, and January, 1924, respectively. IN THE first and second articles you have learned how to assemble and wire your neutrodyne receiver and have found it necessary, after its complete assembly, to adjust it for capacity neutralization. The necessity of such a neutralizing adjustment is characteristic only of neutrodyne receivers. Due to the radical difference of the circuit, the method of tuning is also quite different from the tuning of the usual regenerative or non-regenerative receiver. Consequently, instructions must be very explicit. In this article, we shall accordingly study in detail the method of tuning neutrodyne circuit receivers and in addition, some general information will be given on antennas, vacuum tubes and " trouble-shooting." TUNING THE RECEIVER THE procedure of tuning your neutrodyne receiver, providing antenna, ground, and all battery connections have been properly made, is as follows: 1. Insert the recommended vacuum tubes (See paragraph on the use of different tubes) in their respective sockets and with the power rheostat at its correct position for the type of tubes you are using, and with the vernier rheostat knob turned to the left as far as possible, and with the plug of the loud speaker inserted in the " horn" jack, pull out the knob of the filament switch on the panel front, causing the three amplifier tube filaments to light. 2. Turn the vernier rheostat knob to the right slowly. When the filament current is turned on, the first indication that the receiver is functioning properly will be indicated by a slight noise in the phones. As the rheostat knob is turned farther to the right, this slight sensitivity indication does not increase in volume until a point near the end of the rheostat adjustment is reached. At this point will begin a comparatively loud "hissing" and "frying" noise. For the best signal reception the rheostat should be turned back slightly to a point just before this "hissing" and "frying" starts. 3. With the detector tube at approximately its right operating point, set " Neutroformer" dials 2 and 3 at the same dial setting. Select any particular dial setting, but take for instance the wavelength of station WEAF, 492 meters. Dial settings for this particular station are about 66 or 67. Setting dials 2 and 3 at this point, rotate dial i very slowly over its entire range from o to 100. If any broadcasting station is operating at the particular time at 492 meters, it should be heard at a maximum when the setting of dial i is approximately in the range of 10 or 15 above or below these settings of dials 2 and 3. 4. When signals from any particular broadcasting station are coming in, it is advisable to readjust dials, i, 2, and 3 slightly and possibly also the vernier rheostat, in order to increase the intensity of the signals. In tuning, the dials should be moved slowly. It may be found that the tuning adjustment will have to be changed slightly when shifting the phone plug or loud speaker plug from one jack to another. Dials 2 and 3 should be rotated slowly at the same time, and about in step with each other. Then with dials 2 and 3 on the setting for a particular station, dial i is rotated until signals come in with maximum strength and clarity. Sharpness of tuning of neutrodyne receivers when using short indoor antennas is much greater than when using outdoor antennas. In tuning neutrodyne receivers, the broadcasting stations will not be picked up by hear