An Englishman’s Impressions of AMERICAN BROADCASTING

Radio Record, Volume IV, Issue 39, 10 April 1931, Page 3

An Englishman’s Impressions of AMERICAN BROADCASTING

BADERS will remember read- )| ing in our columns a short time ago.of the visit paid to America by Dr. Robinson, inventor of the Stenode Radiostat, and Mr. Perey Harris, /| president of the Radiostat ' Corporation. ‘In this article, which appeared originally in the ""Wirelegs Constructor," Mr. Harris recerds i ‘iinpressions of American broadcastny, The article is of peculiar interest to us, as it'touches upon, the receiving sets similar to many used in New Zealand. Wnglish conditions, being somewhat different from American, and incidentally from our own, have evolved a type of set that is altogether different from the American type. Upon these differences Mr. Harris makes some interesting observations, jt is five years since I last visited America in the flesh. ,I say "in the flesh’. deliberately, for in these days of simply constructed and highly efficient short-wave receivers one can visit America "by ear" almost any night, and often during daylight, .. But to visit the United States and Ifeten "on the spot" is quite a different matter; and so, within an hour or two of landing in October last I sat down with. pleasant anticipation to listentn. An American Set. "THE set I used followed the present trend of fashion in the States. A. handsome and not too ornate cabinet, about breast-high, with doors which opened and revealed a single tuning control, a kind of keystone-shaped illuminated window showing dial degrees, a volume control, a tone control and a radio-or-gramophone switch. The set easily "plopped" from one station to another as the tuning knob was turned with the volume kept down (I should say about a dozen stations came in in this way), and the quality was good; distinctly good if.the "tone control" were kept on "high." get any more stations it was necessary to turn the volume control well up, with the result that as you _ moved past any local or semi-local stations you nearly blew your head off, and, furthermore, the full volume necessary brought in a tremendous amount of mush and background noise, Still, with all that, it was a very good set in range, sensitivity and quality. The speaker (built-in, or course) was a "dynamic," or, as we prefer to cali it, a "moving coil." A Common Characteristic. I THEN gave closer attention to tone . with the set tuned-in to a station giving good quality (unlike -our: staHions, which are all of high technical quality, American stations vary a good déal), and this revealed what later I found to be a common characteristic. ef modern American sets-a rather pronounced boom in the bass and a peak at about three thousand cycles to give the impression of good "top." These. two peaks--top and bottomhad to be looked for in the particular

set in questin, but in many others I tried later these characteristics were most pronounced. Of a.c, hum there is very little in modern American sets. Careful design of the mains units themselves has something to do with it, but more is due to the increasing use of what are called "power detectors," with only one stage of audio-frequency amplification. : There is a lot of loose talk about power detectors, as if they were something essentially different, but on analysis a power detector differs from the older kind only in being: able to handle a loud signal without appreciable distortion. . By producing as. much as possible of the amplification prior to the detector, trouble from a.c. hum can be practically eliminated, and, furthermore, the cost of the mains unit can be reduced (a highly important point in view of cut-throat competition), as less filtering is required.

In range the sets are quite phenomenal, judged by standards. on this side of the Atlantic, but this is easily understandable when we remember that seven, eight, nine and even ten valves are often used. . The principle adopted is not to force the. utmost out of each valve, but to arrange.a moderate gain in each of several stages, a practice which personally I think by far the best in commercially-built receivers. By having a comparatively small gain per stage two big advantages accrue. Firstly, stability is easily obtained, there being practically no unwanted reaction between circuits, and consequently the individual circuits are not unduly sharpened. This is very important from the manufacturer’s point of view, as a fairly wide tolerance can be allowed in the manufacture of parts.

Important Commercial Considerations, "FOR example, the units in a gang condenser need not to be matched with laboratory accuracy; although, of course, they have to be matched with a good degree of fineness. The coils, too, can be machine wound to a standard which gives easy matching. The second important commercial point about a relatively small gain per stage is that accuracy in matching valves is not required, and the customer can replace his valyes by | any other good ones of ‘":e same type without altering the porformance of. the receiver. Few Types of Valves. NSTEAD of the seemingly needless multiplication of valve types, and considerable difference in characteristies between different makes, which characterise valve manufacture in this country, the United States has only a comparatively few types, fairly uniform in standard. I admit cheerfully that the efficiency of these valves is much below that of ours, but I do know that the American valve manufacturers could easily increase the efficiency if they wanted to, but it is not generally thought advisable. In selectivity the sets are on the whole very good, but not good enough for the existing conditions. To judge by their advertisements, American radio manufacturers achieved a 10-kilo-cycle selectivity long ago, but this is an exaggeration. Regarding ‘Selectivity. ITH comparatively weak’ stations most sets will separate stations on adjacent 10-kilocycle channels, but if one of the stations is at all strong it is quite a different story. I tried a number of different receivers, and found they varied very considerably. Sometimes different examples of one maker’s model vary between themand this certainly applies to some of the newer super-heterodynes. On most sets a strong "local" would blanket two or three channels on each side-some-times more; and as most of the programmes one .wants to listen to come from more or less local stations, a high degree of selectivity is certainly needed. . An Interesting Demonstration, for this reason tremendous interest was shown in the demonstration models of the Stenode’ Radiostat brought over by Dr. Robinson and his party. One demonstration which created quite a sensation was given in a private house within sight of station WOR in Newark. This station was first tuned in, and then as the knob was turned, tuned out, and the next station, WLW (at Mason, near Cincinnati, and only 10 kilocycles away), tuned in quite clear of the slightest interference. Not only was there no interference, but there was actually a blank space between on page 9.)

JOAN OF ARC FR dram atic Radio Play © Produced at 2YA by Mr. J. F. Montague and his Company Monday April 13

An Englishman’s Impressions of America

(Continued from page 3.

could approach this degree of selectivity. When I last visited the States there appeared to be no heterodyning of stations, but this time I heard-a good deal after dark, According to regulations this should not-be, but there .it was all the same. Battery Sets Still Selling. NATURALLY, with the widespread use of electricity practically all sets are a.c., but it will surprise most Bnglish listeners to hear that. there is still a brisk demand for battery sets, and quite recently a new line of 2-volt valves, specially designed for battery operations, with a comparatively low filament current, has been brought out. Farming communities buy most of the battery sets, for although they have electricity on the farms the voltage is often low, and D.C.-of no use for H.T. purposes. Speaking of direct current reminds me that large areas are still supplied with D.C. at 110 volts. A very large part of New York and a considerable area of Chicago are thus supplied. I found that 110-volt D.C. sets. were quite good considering the difficulty of designing a good output stage at this voltage. Push-pull, of course, is a great help here. ;

Tone Control, ARLIDR in this article I referred to a "tone-control" as a fitment on receivers. Many sets have such a control this year. At first it sounds a very useful attachment, suggesting that either high or low notes can be emphasised at will, giving the set user a means of adjusting the set to his own standard of quality. However, use of. the control soon disillusions the discriminating listener. No set, I heard had adequate top-note reproduction with the tone control turned up to the fullest "high," and as one turns the control what top there is is gradually extinguished, giving by the very absence of proper high-note reproduction an iHusion of more bass. A very nasty business to the musically minded! If, and I say if with emphasis, a set has too much top, then means can be adopted for reducing the top rendition. A tone control consists of a condenser of about .004 or .006 mfd. in series with a continuously variable resistance of about 250,000 or 500,000 ohms, this combination being placed across the output of the set. If you think for a moment you will see that a resistance of, say, 200,000

ohms in series with a .004 mfd. practically cuts it out of circuit, but if the resistance is lowered to a few. hundred ohms then we have a state of affairs practically equivalent to shunting the speaker with .004 mfd., a value of capacity which will very effectively by-pass a large proportion of the higher frequencies. _ Between these two limits a wide fange of by-passing is possible. . Just such a device is the much advertised tone-control of modern American receivers, And a whole lot of people like it! They call the result "mellow !" -On the other hand, cutting off the higher frequencies also cuts off a lot of high-pitched background noise, as well as needle scratch in radio-gramo-

phones. The first is useful in longdistance listening with the volume control turned full on. ' Interesting Construction Details, Axbour the second, opinions differ, many people thinking that the advantage of reducing needle scratch is too highly paid for by the loss of brilliance in reproduction. The constructional details of modern American receivers are very interesting to the home constructor. Stiff wiring has entirely disappeared, due in the main to the risk of broken joints due to vibration from factory to dealer and from dealer to user, All those wires which can run together without harm-and a surprising number can!-are bunched and "cabled" in flexible leads, and even the separated wires are of the stranded or flexible type with insulating cover- } , To distinguish them in assembly and fault, tracing the wires are differently coloured according to their particular circuits, and connections are generally made with eyelets of the stamped

variety, screwed under nuts which are held secure with shake-proof washers, Component Design, CHASSIS construction is universal, either aluminium or steel. being used.. Soldered connections are cut down to the minimum by careful design, and when you realise how much of the cost of a set goes in labour, the saving of a few, joints and the reduction of assembly processes are very important manufacturing considerations. . Components are designed with ease of assembly in mind, and astonishing simplifications have been brought about in dozens of ways. Valve holders, for example, consist generally of: five holes stamped out of a thin strip of bakelised fibre, or stamping rivetéd on to the underside to form contact with the valve pins. You may think this shoddy manufacture, but such sets work well and give far less trouble in servicing than the older forms of construction. Mains units are fairly well standardised in these days, and valve rectification is practically universal in fac-tory-built sets. America’s "Midget" Sets. . OF late, due to the financial stringeney, and consequent reduction in spending power of the public, the s0called midgets sets are becoming very popular. The American midget set about the size of our larger cabinet loudspeakers, and contains a five or six-valve mains receiver with two or three stages of radio frequency, and a moving-coil speaker, Single-control tuning is, of course, standard here, as in all other receivers, and the sets are made to work on amall exterior aerials. Their range is limited in comparison with the larger _ sets, but they put up an astonishingly good performance for. their price, which averages about £14 in English money.