RADIO RECORD

Greymouth Evening Star, 19 December 1933, Page 9

RADIO RECORD

NOTES FOR LISTENERS-IN

(By

“Reception” )

multi-grid valves. ACCOUNT OF ADVANTAGES. The following is a brief outline of the bewildering combinations in valve design now on the market. During the past few months a number of entirely new valves have appeared on the market, and there arc strong rumours that more are to follow, says “Popular Wireless.’’ The, list so far includes the “Class B.’ Double Diode Triode, and DoubleDiode Pentode. Two more we may confidently expect to arrive soon are the Pentagrid Converter and the “Q.P.P.,” as we may tentatively term it. Those readers who know of these valves only through seeing them buried in the middle of complicated-look-ing circuits may well consider them to be extremely advanced productions. But actually they are not. No vitally new fundamental principles are involved. In fact, we can safely say that these new valves herald a kind of portmanteau era in valve design. Nevertheless, they are none the less important for that. These words are not being written with any depreciatory intent, but merely to show the home constructor that he need not jump to the conclusion that with the new valves radio has taken a leap from comparative, simplicity into a condition of bewildering complexity. All the general principles which guide one’s understanding of the theory of straightforward circuits using normal valves still apply; but, instead of using separate valves for each separate duty, valves capable of carrying out several tasks each have been introduced. . The “Class B” valve is essentially a pair of ordinary triodes (three-elec-trode valves) built into one bulb.. “Class B” is, in short, a specialised system of push-pull There are several advantages in combining the elements of two valves in one bulb. The most obvious is that one article replaces two, and space and wiring are economised. A point of even greater importance is that the necessity of matching two valves —for they must both be of identically similar characteristics and operate under exactly similar conditions —is entirely eliminated. The Double-Diode Triode combines a diode having two anodes with a three-electrode valve. This latter section is generally used as a straightforward amplifier, while the diode part, which can be regarded as quite a sep. arate entity, is available for detecting and for automatic volume control. The Double-Diode Pentode is the same kind of valve as above, only, as its name suggests, a pentode section replaces the triode. The Pentagrid Converter (or Hexode) is a special super-heterodyne valve in which a three-electrode oscillator and either an S.G. or Pentode Detector are built into one bulb. The latter is designed so that it has var-iable-mu characteristics, and these enable automatic volume control to be applied. • . The advantages of this portmanteau” valve arc that the “mixing of the input and oscillator frequencies is purely electronic, i.e., is done inside the valve and a consistent performance over the whole waveband, with practically no coupling trouble results. The “Q.P.P.” is the name we ourselves have given to a. new . valve which, at the time of writing, is still in the experimental stage. But there is little doubt but that it will in due course appear. This, too, is a simple enough propo,sition; it is a couple of pentodes for quiescent push-pull enclosed within the single envelope.

HUMAN EARS. It is a very remarkable fact indeed that the ear is capable of supplying the fundamental to a note when only the overtones or harmonics of the note are present. Small horn loudspeakers, gramophones of the old type and similar speaking instruments never used to be able to supply bass notes much lower in'pitch than Middle C (256 cycles). The fact, therefore, that with their use we did hear lower notes to some extent results from the marvellous property of our ears for actually supplying fundamental tones which were entirely absent from the reproduction. Another curious property of the ear is that it can render itself very sensitive to faint sound and very insensitive to extremely loud sounds. If when a certain limit of sound intensity has been attained, further energy is put into the vibrating system or mechanism, there is not much increase in the intensity or loudness of the resulting sounds. In fact, as the intensity of a source of sound is increased (particularly when the sound is deficient in lower jiiotes) there comes a point at which the sound produces a tickling and even an actually painful sensation in the ears.

You can easily test the sensitivity of the hearing to variations in soundintensity by connecting a variable resistance across the terminals of a loudspeaker. Let the subject of the experiment sit with his back to the speaker, and then, when you are gradually varying the resistance placed across the speaker terminals, get your subject to inform you immediately he is aware of any increase or decrease 01. the sound's intensity.

A few simple experiments in this direction will pretty soon convince you that not only are different pairs of ears of different sensitivities, but also that, as a general rule, their power of differentiating between fine degrees of “loud” and “soft” is very severely limited.

STIFF HBADS Did you know that, if at any time you have a terminal head which turns stiffly on its shank, the quickest way of making it turn easily is to hold it on the edge between the lirst finger and thumb against a hard surface and then severely rap it with a hammer m several different places? Contrary to belief, as any engineer will tell you, this doos not close up the bole —it opens it! Did you know, too, that only on the rarest occasions will a nail split the wood into which it is driven if the end of tho nail is first flattened with a hammer*

CONDENSER VALUES With the very large number of different types of condensers which are now available the ordinary man gets rather confused on the question of capacity values, and unless you arc continually handling condensers for different purposes you are liable to go wrong on a decimal point, which means multiplying or dividing by 10, and makes a lot of difference! It might perhaps be useful to mention the purpose for which different capacities of condensers are generally used. For instance, the very small capacities, say, 0.00005 up to about 0.0005, are generally used for aerial tuning, the smallest values being for aerial selectivity adjustments. Values ranging from .0003 to .0005, are also used for tuned anode, and for highfrequency transformer tuning, while fixed condensers having values of about 0.0001 to 0.0003, are often used for high-frequency coupling detector anode bypass and power-grid detectors. Coming to higher values, resistancecapacity coupling takes 0.001 up to many times this value, even as high as 0.1, while this latter value is also useful for high-frequency bypassing. With parallel-feed transformers you can use from 0.05-microfarad right up to 1 micrafarad or even up to 2 microfarads. For low-frequency decoupling, condensers of 1 or 2 microfarads may be used, while for smoothing circuits, as in a mains-supply unit, you can use 2 or 4 microfarads, and, in fact, go to electrolytic condensers with very much higher capacities. TO-DAY’S PROGRAMME. IYA AUCKLAND (650 kc). 5.0: Children’s hour. 6.0: Dinner music- 7.0: News and reports. 7.30:, Talk, Book Reviewer, “Book Review.” S.O: Selected recordings. 9.0: Weather forecast and station notices. Reserved. 9.20: Recordings. 10.0: Dance music. 11.0: Close down. Alternative programme (IYX, 880 kc): _5.0; Musical programme. 6.0: Close down. 7.0: After-dinner music. S.O: Alternative concert programme. 10.0: Close down. . 2YA WELLINGTON (570 kc.). 5.0: Children’s hour. 6.0: Dinner music. 7-0: News and repoits. 7.10. Lecturette, Representative Agricultural Department, “For the Man on the Laud.” S.O: Recordings. 8.26: Mr Ronald Chamberlain (pianoforte) (a) "First Romance”; (b) “Second Romance”; (c) “The Phantom Horseman. 8,36: Recording. 8.40: Talk, Representative British Medical Association, "Cancer is Curable.” 9.0: Weather report and station notices. 9.2: Special presentation of “The Elysian Fields, a, radio drama by Bernard Cronin; produced by Mr L. J. Maule. 9.40: Mr Ronald Chamberlain (pianoforte), (a) “Three Studies, On. 8”; (b) “Polonaise in C Sharp Minor”; (c) “Fantasie Impromptu.” 9.50: Recording. 10.2: Close down. Alternative programme (2YC, S4O kc.): —5.0: Musical programme. 6.0: Close down. 7.0. Alteidinner music. 8-0: Alternative concert programme. 10.0: Close down. 3YA CHRISTCHURCH (720 kc). 5.0: Children’s hour. 6.0; Dinner music. 7.0: News and reports. 7.35: Talk, Miss Scott-Baker, “Books.” 8.0: 1 Special Studio Presentation entitled “British Sea Dogs in Song and Story by A. G. Thompson and Company. 9.15: Weather report and station notices. 9.17: Selected recordings. 9.30: Dance music. 11.0: Close down. 4YA DUNEDIN (790 kc.).

5.0: Children’s hour. 6.0: Dinner music. 7-0: News and reports. 8.0: Thirty minutes of recordings. 8.30: The Chorus Party, “Sweet and Low ; (b) “The Viking’s Song.” Mr Eric G. Williams (trombone) (a) “The Favourite”: (b) “Lay My Head Beneath a Rose.” Recording. The Chorus Party, (a) “At Eventide” (Raff); (b) "0 Who Will O’er the Downs so Free. ’ Recording. 9.0: Weather i eport and station notices. 9.2: Talk, Mr Martin F Cock “Historical Subjects—The Tower of London.’ ” The Chorus Party (a) “Moonlight”; (b) “Londondeny Air.” Recording. Soprano, Evelyn Shepard, (a) “Have You Seen a White Lily Grow?” (b) “Rose Softlj r Blooming” Mr Eric G. Williams (trombone), (a) “The Switchback”; (b) ‘lntermezzo from “Cavalleria Rustical) a.” The Chorus Party and R. Dunbar, (a) “Medley of Sea Shanties ; (b) “By the Sea.” Recording. 10.1 a: Close down. EMPIRE STATION, DAVENTRY. Transmission 1.: 8.0 a.in.: Time Signal Hom Big Ben. News bulletin. 8 15: Foreign Affairs, a talk by Mr Vernon Bartlett. 5.30: Scrap Book by Leslie Bailey. (Time Signal from Greenwich at 9.0 a.m.). 9.00-10.0: Organ Recital from the Concert Hall, Broadcasting House, London. Transmission II.: 12.0 (noon): lime Signal from Big Ben. Reginald New at the organ of the Regal, Kingston-on-'l liames, Surrey. 12.30: The Commodoie Grand Orchestra, directed by Joseph Museant, relayed from the Gem modorc Theatre, Hanunersniith, London. (Time Signal from Greenwich at 1.0 n.m.). 1.15-1.45: An organ recital. (Gi eenwich mean time.)