RADIO

Southland Times, Issue 20111, 23 February 1927, Page 14

RADIO

NEWS AND NOTES By “Reflex.” Last Friday evening found 2FC on the air with an excellent programme. Among the items were: The popular musical comedy “Hullo Healo” written by Ken Duffielf, Australian composer, in association with D. Titherago and Mr Sydney Smith's reminiscnces or the Australian cricket tour; From the studio there were violin solos by Mr L. Lawson, and Miss P. Dunbar and other musicbl items. Radio listeners look for novelty, and will hear something to their liking on Sunday evening, March 6 from 2FC. A visiting Mexican journalist, Mrs Consuelo de Aldag, now resident in Sydney, has an interesting talk to give concerning the quaint old customs of her country, which will be interspersed with a number of Mexican songs not previously heard in Australia. The manuscripts are in the sole possession of the lady, and they will be interpreted by Miss Annie Payne, mezzo. In addition some unusual South American records are to be played. A surprising amount of dust finds its way into the necks of horn type speakers. It is a good plan to unscrew the horn periodically, and to blow out any accumulation that is visible. You may possibly find a dead moth or Christmas bettie, which has caused you no end of trouble. A film of dust or dirt which has accumulated between the terminals of a receiver will often act as a resister, which may appreciably affect the operation of a sensitive circuit. Motto: Do not allow dust to accumulate anywhere, but remove it with a feather duster or soft cloth as soon as you notice Rain water is quite all right for topping up accumulators, but should be collected in an earthenware pot out in the open spaces, not under down pipes or verandahs, since iron drippings and other foreign matter will enter the water. When wiring up a receiver do not put in an .001 because you have one; if the circuit specification tells you to use a .00025, always keep to the size specified. Just because the .001 hapens to work is no reason for its use, the correct one is sure to give better results. Fixed condensers of the best make procurable should always be used, as if the insulation between the plates is of inferior quality, a break down will frequently take place, and noise will result. Bad noises have often been traced to this cause, more particularly a leaky or broken down grid condenser. For those who are handy with tools and do not desire to scrap existing big condensers, it is posisble with most types to undo the moving plates and take out every second plate, and fill in the space with a metal washer of the same thickness as the discarded plate, in this way the capacity of the condenser can be very much reduced. THE NOISY B.C. RECEIVER Many broadcast listeners are very annoyed when, in the middle of some important or particular item which they do not want to miss, whistles or deep-toned howls are heard in the 'phones. It is often the simplest thing that causes the most trouble. For example, leakage across the base of the valve sockets often causes peculiar whistling sounds, which can be remedied by carefully cleaning them. Another very important point (often neglected) is to keep the vanes of the variable condenser free from dust. Faulty windings in the headphones, transformers, or loud speaker, or a few broken strands of the loudspeaker cord, may cause high and shrill whistles. Reaction used in excess or improperly and unskilfully used causes much unnecessary annoyance. So much has been said about this subject that it is only proposed here to give a fairly good and reliable test for oscillation. Touch the aerial terminal with the finger; if a click is heard in the 'phones, both when the terminal is touched and when the ringer is removed, then the set may reasonably be supposed to be oscillating. This can be remedied by reducing the coupling of the reaction coil or by reducing the filament current or plate voltage. Just a little experimenting will often ensure smooth working. BREAKDOWN OF AUDIO TRANSFORMERS It is rather to be noted that the percentage of breakdowns experienced locally n regard to audio transformers is rather high. This trouble is not confined to the products of one or two individual manufacturers. It is spread fairly evenly, taking into account ratio of sales. As more of the most important and reliable makers have oeen giving unconditional guarantees with their products the higher percentage of ‘‘duds” has been noticeable. In the majority of cases it is the primary that fails. As many of the makers have been informed pretty thoroughly by their agents here of the particular climatic conditions with which we have to contend they have evolved what their experiences proved suitable to stand up to requirements. It may seem an unusual thing to say, but it is the writer’s candid opinion that in many cases the audio transformer, irrespective of what make it may be, is not given a square deal. Probably in the great majority of cases there are first and second stage jacks, or medium and loud, as the case may be. Incidentally the set is also equipped with a battery switch, but except for pulling it out at 6.15 p.m. and pushing it in again at 12.30 a.m. it is never used. Every time the plug is to be placed in the other jack the filament switch should be “off.” If the set is in full operation and the plug is changed from one jack to another a sudden surge is impressed on the primary of the audio transformer, and then one day the trick is done. It is that sudden surge that is responsible for the majority of the breakdowns. Should your set not be equipped with a filament switch put one in. DEVELOPMENT OF RADIO INCREASE IN LICENSES. The Postmaster-General (Hon. W. Nosworthy) in officially opening the new radio transmitting station, 3YA Christchurch, delivered the following speech—“At Auckland, six months ago, I had the privilege of declaring officially open the first of the Broadcasting Company’s new stations. That occasion marked the passing of the first milestone, and the transition from make shift to organised radio service in New Zealand. To-night we pass the second milestone of the Dominion’s progress in the broadcasting branch of radio science; and I i hope that before many more months have passed we shall reach the third stage with the completion of the larger station proposed for Wellington. “This fine new station will be doubly welcome. The electrical plant and the studio equipment are the most up-to-date obtainable. The installation is of the highest efficiency yet developed, and would be an acquisition to any city. “Since the Auckland station was opened, radio in this country has made rapid strides, the most striking advance being the increase, during the short time that has elapsed, in the number of licensees. There were then only 4,500. To-day we have 16,000. On a population basis, this repre■ents an approximate increase of from 1 in 300 to 1 in 80. Hundreds of applications are still pouring in; and we are confident

of reaching and even passing the mark at which we are aiming. Unfortunately the remarkable growth has brought in its train an aggravation of the howling valve nuisance, the elimination of which constitutes a difficult problem that is engaging the serious efforts of the Post and Telegraph Department’s experts. Listeners can themselves do much to alleviate it by educating their less experienced fellows in the proper operation of their sets; and I would strongly urge them, in their own interests, to supplement in that way the efforts of the official inspectors. “The unlicensed listener, deservedly known as the radio ‘pirate,’ is a less direct but just as potent an obstacle to the attainment of a first-class service as the Oscillating Oswald’; but an active campaign has been organised against the ‘pirate,’ and it will be seen from police court reports that he is being made to ‘walk the plank’ when captured. It may not be generally known that one of the trial measures adopted is to encourage by reward every officer of the Post and Telegraph Department to report the existence of unlicensed sets. This scheme has not been long enough in force to gauge its effect; but it has greatly added to the possibility of detection, and cannot fail to disturb any sense of security the ‘pirate’ may have had in the past. “It may interest you to know that during this year there will be held in Washington an International Radio Telegraph Conference, and one of the matters which will probably be considered is that of abolishing the 450 and 600 metre wave lengths for ship stations, and allotting ones that will be well beyond the broadcasting band. Interference from ships has been largely prevented in the meantime by prohibiting their use of the 450 metre wavelength within 400 miles of the coast during the evening, and within 100 miles during the day. “A phase of broadcasting that will receive a great deal of notice in the near future is the re-broadcasting of programmes. Experiments are now’ being made which, if successful, will enable programmes broadcast from England to be received at large receiving stations in the Dominion and retransmitted for the benefit of local listeners. There is at present no station in the Old Country of sufficient power to carry out this work; but, when one is erected, it will give us our most intimate bond of communication and interest with the Homeland, and prevent broadcasting from becoming the medium of the un-British influence for which the film industry has unfortunately provided a vehicle.” PHILLIPS SPEAKER GETTING THE BEST RESULTS. (Contributed.) A receiving set that is not properly constructed cannot be expected to give firstclass results. In many cases, however, an unsatisfactory set can be improved by slight alterations. It is particularly necessary when using a Phillips Loud Speaker that the set should be as free from distortion as possible, as this new Loud Speaker, unlike the older types, reproduces the whole range of audible notes, owing to its being made on an entirely new and patented principle. The reed which conveys the mechanical (sound) vibrations to the conical diaphragm is set between two Electromagnetically controlled magnets and, therefore, reproduces perfectly the lowest base and the highest treble notes. Some of the many cases of bad reproduction of sound owing to distortion are dealt with below. Distortion and impurity in reproduction can be due to a fault of—(1) the low-frequency amplifier, (2) the detector circuit, (3) the high-frequency amplifier. The Low-Frequency Amplifier. Distortion in the low-frequency amplifier may be due to—(1) incorrect negative grid-bias, (2) overloading of the tubes, (3) transformers of poor quality or wrong ratio, (4) the presence of high-frequency oscillations, in the low-frequency amplifier, (5) oscillation of the low-frequency amplifier. I & 2. Overloading can be avoided by using tubes adapted for power amplification. The choice of a low-frequency amplifying valve is determined by the amplitude of the grid-voltage variations to be expected. The grid should never be allowed to become positive with respect to the filament whilst the valve is in function. If this should happen, grid currents would be produced, giving rise to distortion. When the voltage-variations of the grid, for example, attain a maximum value of 7.5 volts, the grid should be made negative with respect to the filament by means of a battery of at least 7.5 volts. The grid voltage will then vary from—ls to 0. In this grid voltage range the characteristic should be as straight as possible, as otherwise the fluctuations of the plate-current would not be proportional to the grid voltage variations, with consequent distortion. The larger the grid-voltage variations the higher must be the negative grid bias. In the case of strong amplification the lowfrequency oscillations on the grid of the last valve may reach 15 volts or more. In that case the use of a valve of the type Philips 8403 which allows the use of a negative grid bias of 15-24 volts at a plate-voltage of 120 volts is essential. It is of the utmost importance that a sufficiently high platevoltage should be applied to the low-fre-quency amplifier-valves. 3. When the transformers used are not of first-class quality an appreciable improvement often can be effected by connecting a resistance of 70,000-100,000 Ohms ® parallel with the secondary. This, of course, causes loss in volume. The first transformer should have a ratio of 2.7 : 1 to 4 : 1 the second 4 : 1 to 6 : 1. 4. High frequency oscillations which occur in the plate-current of the detector-valve must be prevented from passing into the low-frequency-amplifier. For this purpose a condenser of from 0.001 mf to 0.002 mf should be connected in parallel with the primary of the first low frequency transformer. This condenser constitutes a bypass for the high frequency oscillations. If resistance amplification is used the condenser should be placed across the plate resistance of the detector valve. It is also advisable to place such a condenser across every following plate resistance. 5. I€ multiple transformer-coupling is used it may happen that the low frequency amplifier oscillates at an audible frequency; this frequency, however, may also lie beyond the audible region, resulting in bad distortion in both cases. Oscillation may be eliminated by reversing the connections to the primary or to the secondary of one of the low-frequency transformers or by mounting a resistance of about 100,000 Ohms in parallel with the secondary. Earthing the cores may also lead to improvement. When constructing a low-frequency amplifier, care should be taken that the transformers are not placed too close to each other and that the cores are at right angles. This prevents mutual coupling of and interaction between the transformers. The Detector Valve. For good detection a correct value of grid-condenser and grid-leak is of the utmost importance. The grid-condenser should have a capacity of 0.0002 to 0.0003 mf; the grid leak should be about 4.3-3 megohms. It is advisable to connect the leak between the grid and the sliding-con-

tact of a potentiometer connected in parallel with the filament. By this means the best working point can be found. Care should be taken against too strong a reaction, as it results in bad distortion. The High Frequency Amplifier. The high frequency amplifier may oscillate when the set is tuned. In such cases improvement may be effected by connecting a resistance of 10,000 to 20,000 Ohms in parallel with the tuning coil of the gridcircuit. Also reduction of the plate-voltage of the high frequency-valve often suffices. H.T. BATTERIES A peculiarity is very evident by many in the purchase of high tension batteries. Many sets require •./ 22j volt tapping for the detector circuit. The nett result is that if a 45-volt block is used the lower, or 221volt portion, depreciates more quickly, until finally it must be discarded, although the other portion may be quite serviceable. It is far better policy to use two 223-volt blocks in this position instead of one 45volt. When the first 22j -volt has reached a state of uselessness it can be replaced much more cheaply, being only half the price of the 45-volt. Another point overlooked by many: It is better policy, if operating multi-valve sets, to use the extra size batteries now available for the heavier work. Although the expense is a little more in the first place this is amply repaid in the long run by ensuring more satisfactory service.