Radio age (Jan 1927-Jan 1928)

12 RADIO AGE for October, 1927 "1928 Infradyne" Presents Attractive New Features AMONG the new radio receivers and equipment for the 1928 radio sea■ son we find the "1928 Infradyne" one of the most distinctive. Here is a radio set embodying really new features ; interesting alike to the man who builds his own set and to the professional set builder. All the difficulties a man encounters in building, such as the tedious alignment of the tuned radio frequency stages, stabilizing, preventing inter-stage coupling, etc., have been removed before the parts for the set reach him, and he has a much better chance of immediately getting perfect and gratifying results; still there is the satisfaction which every radio fan knows, derived from having constructed one's own set. The assembly of parts and wiring is a matter of two or three hours of interesting work and the result is a receiver which not only has the appearance of the finest factory built set, costing considerably more money, but also performs like the best of them. The creation of this set is certainly a progressive step in the industry. Ten tubes are used throughout the set, two CX301As in the first two stages of tuned radio, one in the first detector socket, one as the second detector, and also one in the first stage of audio; three CX399 tubes are used in the Infradyne Amplifier unit and one more in the oscillator socket. Either a CXI 12 or CX371 is recommended for the last stage of audio. The photo, Figure 1, shows the set as it looks completely assembled and housed in an all-metal cabinet, which provides an effective shield against picking up radio frequency and other electrical disturbances by the coils and associated wiring in the set, permitting only energy which is picked up on the antenna and going through the tuned channels to be amplified. Through the efficient shielding and very selective circuits all but the desired signals are rejected. The tuning controls or selectors are the two upper knobs on either side of the voltmeter, connecting with the two drum indicators which are mounted, one on the three-in-line Remler gang condenser to the left, and the other on the single Figure 3 — Radio frequency amplifier with the metal case removed Remler condenser to the right. A filament control is directly beneath the voltmeter, the voltage applied to the tubes being indicated on the meter. A volume control is on one side and "sensitivity" control on the other, both of these are rheostats mounted behind the condensers ; extension shafts connect the rheostats with the knobs on the front panel. A switch at the bottom of the front panel controls all the filaments. When the switch is at the "OFF" position all the filaments are out; when it is turned to "LOCAL" position the Infradyne amplifier is out of the circuit and only the radio frequency tube and audio frequency tubes are lighted-, and when the switch is turned to "Distance" all the tubes are lighted and the Infradyne Amplifier is automatically put into operation. Just above the base and to the left of the central control panel is a supplementary bronze shield carrying the antenna compensator control. The antenna compensator control knob is double, the larger part operating a three-point switch permitting variable antenna coupling and the smaller part controlling a small variometer connected in series with the secondary of the input radio frequency trans Figure 1 — The receiver as it looks completely assembled and housed in an all-metal cabinet former or antenna coupler. Adjustment of the antenna compensator is made when the set is first put into operation after which the antenna circuit will stay in line with the remaining circuits over the entire wavelength band. A very slight adjustment of the antenna compensator might be desirable as a last step in obtaining the best possible reception of a distant station but under ordinary conditions it can be forgotten when it has once been correctly set. In the rear of the cabinet, at the end nearest the antenna compensator controls, are the "Antenna" and "Ground" binding posts, the battery cable and the jack for the loud speaker. The whole receiver is made up of several units which are easily assembled. One of the most interesting features is the all metal base, with holes already drilled, and the completely assembled radio frequency amplifier which constitutes the front part of the set. The photo, Fig. 2, shows the complete layout of parts and the photo, Fig. 3, the radio frequency amplifier with the metal case removed. The r.f. amplifier is unique in many respects, and shows real engineering on the part of the designers. The three transformers are tuned with the single Remler three-in-line condenser to which is mechanically connected a shaft having the primaries of the transformers mounted thereto; as the capacity of the condenser is increased the coupling between primary and secondary of the transformers is increased, in a relation which tends to keep the greatest sensitivity without oscillation over the whole wavelength range ; also, provision is made for two degrees of primary to secondary coupling so that the amplifier is readily adaptable to various broadcast conditions. The coupling can also be changed by moving the secondary coils which are mounted on brass rods extending up through the center of the coils, up or down, thus changing the relation of the secondary to the primary coils. The coils are matched with the gang condenser at the factory, this eliminating trimmer condensers to compensate for deviations in the coils as the wavelength range is covered. For greater selectivity the coils are moved upward and for less selective tuning the coils are moved down. Shields between stages minimize interstage coupling; together with the automatic coupling scheme, the amplifier is very stable over the whole wavelength range, and also at maximum sensitivity over the whole range. The front part, or radio frequency amplifier, of last year's infradyne was in some cases rather difficult to handle. In the new Infradyne this complication is eliminated. At the rear of the set is mounted the Infradyne Amplifier. This is the same amplifier which has become so well known during the past year for its ability to sharpen tuning and to build up volume of signal without an annoying increase in background noise. In construction and per