Radio age (Jan 1927-Jan 1928)

RADIO AGE for October, 1927 SO O O O^n m ^ fZZO *2Z0 *Z2 f A typical split-loop Superheterodyne circuit with the Jewelers' Amplifier substituted for old Intermediates In adapting the time signal amplifier to super-heterodynes that have been built previously our task is very simple. The outward appearance of the old set can remain exactly as it now is, the controls in no way being different. This is of considerable importance because it means that the new catacomb can be dropped right into the receiver in place of the old I. F. amplifier. As a matter of fact there is but one control for the time signal amplifier, the oscillation control which is simply the conventional potentiometer. In substituting this efficient time signal amplifier, therefore, in place of our old intermediates the front end of our super and the A. F. amplifier remains exactly as it was. The customary first detector and oscillator stage are not affected, the catacomb merely displacing the old intermediate stage and the second detector. Inasmuch as the Jewelers' Time Amplifier is but 15" long, 5" wide and 3" deep we will usually be able to displace the units which are being removed and find room to spare. The audio amplifier system of the receiver, providing of course that it delivers the tone quality that we demand today, remains intact exactly as it is. On the Jewelers' Time Amplifier we will find eight binding posts, four on the left hand side and four on the right. The left hand side binding posts are marked N, +90, B and P. The N terminal is connected to the center arm of the potentiometer on our panel and controls the oscillation of the intermediates (a ^ or 1 mf. bypass condenser connects across the arm and minus end of the potentiometer). We all know that with an intermediate amplifier the closer we approach to the oscillating point (toward the negative side), the more sensitive the receiver becomes and with a proportionate volume increase. This control works exactly the same in the time signal amplifier as it does with ordinary intermediates. The +90 terminal connects to the 90 volt B battery line. The terminal marked B connects to the 45 volt battery line and the terminal marked P is the one that is connected to the plate of the tube socket of our first detector — this carrying the signal from the detector tube to the first stage of the time amplifier. A choke coil should be included in this lead, such as the S-M 275, if a split loop circuit is used. On the right hand end are four terminals marked — \y2, P, — 6 and +6. The terminal marked — ¥/2 goes to the negative of our 4H volt detector C battery. Rectification of the signal in what then becomes our second detector, which is the detector in the time amplifier, is brought about by the use of a C battery rather than by a grid condenser and leak, because of the advantages of greater handling capacity. The P terminal carries our signal to the first audio transformer. The — 6 terminal is negative A battery lead and the +6 terminal is the one going to the positive side of the A battery. In the time signal amplifier we will find that the negative A terminal is grounded, in other words, the entire housing as well as the shields in the housing that separate each stage from the other are connected to A—. Inasmuch as the Jewelers' Time Amplifier is completely wired the matter of bringing an old super-heterodyne up-to-date requires but a very few hours. In all probability it will take longer to tear out the old intermediates than to substitute this new unit. With this substitution the old superheterodyne is not only brought up to date but a careful search of what the market affords has also definitely demonstrated that there is nothing to be had that will give the results of the renovated receiver. As has already been said the Jewelers' Time Amplifier with an amplification factor of approximately 10,000 gives us an amplification gain in the intermediate stages far beyond that to be found in ordinary amplifiers. Comparative laboratory tests have shown that through the use of the time signal amplifier owing to its tremendous per stage gain, distant stations could be brought in with loud speaker volume barely audible with other sets with an equal number of tubes. The selectivity is such that in Chicago it will allow reception of out of town stations within 10 K. C of powerful locals. 90,000,000 Radio People Approximately 90,000,000 of the 1,000,000,000 people living within the world's constant radio reception area receive radio broadcast programs, in some form according to a report on potential markets for receiving sets by Lawrence D. Batson, Electrical Equipment Division, Department of Commerce. About 18,000,000 receiving seta are now in use, according to Batson, who estimates that 200,000,000 sets would be required to service all of the people within the constant reception area on a basis of five members to each family. Fifty-seven foreign countries now maintain regular broadcast service with Canada, Cuba, Russia, Sweden, Australia, Germany, United Kingdom, Argentina, and Mexico ranking first in order of number of broadcasting stations maintained and regularly operated. Radio broadcasting, according to Batson, has attained as great importance in international, national, and family life abroad as it has in the United States, all circumstances considered, and has now been recognized by all of the principal foreign governments as an important means of disseminating entertainment, information, and instruction. Radio programs have a striking similarity all over the world and jt is not without some basis of possibility that programs broadcast throughout the whole universe may be expected to prove more popular than those of local origin, the report states. More news and some direct advertising find place in foreign programs and government communications are formally presented to the people through the microphone, but in general a typical American program is likewise typical for any part of the world, according to Batson. Congestion of broadcasting stations has occurred so far only in the United States, Canada, and Europe. Mexico City, Buenos Aires, Sydney, and Melbourne and a few other cities having sufficient number of stations to require particular attention to wave lengths in order to prevent interference but their problem has been simplified in these places by the fact that the full wave band is available. These cities are favored, too, by the fact that there are no other stations operated in close proximity to the city limits, according to the report. North America and Europe have broadcasting stations scattered throughout the inhabitable area. South America is well served except in the interior and the extreme northwestern part of the continent. Other developments are spotty except in Australia and New Zealand where stations are well distributed. Some foreign countries regulate radio broadcasting on a strictly commercial basis with broadcasting corporations holding exclusive or quasi-exclusive concessions. Where such regulation is enforced, owners of receiving sets are usually assessed a fee for reception privileges, according to Batson. In countries where monopolies do not obtain, any person or firm showing satisfactory general qualifications is granted permission to operate a broadcasting station. In a few countries where unusual political or economic conditions prevail, the possession of broadcasting and reception equipment is rigidly denied, according to the report. SEE NOVEMBER ISSUE FOR SUPERHET CIRCUIT WITH NEW FEATURES