Questions and Answers

Radio Record, Volume IV, Issue 52, 10 July 1931, Page 13

Questions and Answers

DETECTOR (Auckland).-I recently changed my set from a metal cabinet to a wooden one, and whereas the coils would once tune between 200 metres and 650, they will now not cover the band. I rewound the primary of the regeneraformgr, slightly spacing it, as advised in "Deof R.F. Transformers." -A.: Your trouble does not appear to be an obvious one, and it can be explained only if you have made some slight alteram in the wiring. It is posible that you have brought about certain capacity changes. These could be the result of closed loops in the filament winding, a different, relationship between the plate and grid wires or some similar changes, Metal near the coils will have the effect of altering the tuning range. PUZZLED (New Plymouth).---I have a 5-valve commercial neutrodyne, the valves of which have been in use about 12 months Could you tell me if they are the right type? Four are 201A and the Jast valve is C608. . A.: We recommend for the last stage B605, and instead of the 201A, the new 221 type. 2. What ig the correct value of the grid-leak? uk A.: In a broadcast set the best results gan be generally obtained by a 2 megohms leak, GQHORTY (Stratford): How many grid and regeneration turns have to be wound on a valve base former using 30 gauge d.s.c. wire to cover the 80 metres’ band using a .00005 midget condenser? A.: 24 on the grid and 17 on the regeneration coils, . Some time ago Q.R.L. wrote a series of articles describing a low-powered transmitter. Would it be possible at some

future time to describe a Heising modulator for this transmitter? A.: We have approached Q.R.L. on the subject, and it is possible that at some future time an article such as you desire will be published. GHYLOCK (Hokianga).-_Would’ my aerial be better strung from a 300ft. hill than in its present slightly-shielded position? A.: From what we can gauge from your letter, it would be an improvement to put the aerial on the 300ft. hill. It is impossible, however, to lay down anything definite until we saw a sketch of the neighbourhood. . 2. Would the aerial be better on gq piece of reclaimed mudflat, where there ate no trees and few surrounding hills? A.: Where has that 300ft, hill gone to if it is nowhere near the mudflat? Surely you must have to use a very long head in for one of the positions, Certainly an aerial should be erected away trees and hills. These have a definite screening effect. . 8. Which of the two would be the better? A.: We think the former A W.M. (Dunedin): My set tunes * very broadly, and I get the Dunedin "B" class stations and 4YA all over the dial, I have tried a s.g. booster described in the "Radio Record," but it makes volume much weaker, A.: There igs something wrong with the booster. Generally boosters have gone out of date. It is far better to use a s.g. valve in a modern transformercoupled hook-up than as a separate unit. It would be far better to use your parts to reconstruct the set along modern lines using a circuit such as the Outspan Five. Although these are not as selective as the very modern receivers, still they are a vast improvement on the ordinary two triode r.f. stage sets or the single screengrid type. They are reasonably selective and should be quite satisfactory for your purpose, 2. Could the set be made selective withgut much alteration? A.: The easiest way to make a set selective is to vary the coupling between the primary and the secondary of the aerial coil. By making the coupling looser the stations can be separated much easier, but, of course, a certain amount of sensitivity is lost. 8. I use B406 in the first audio stage ant bas in the second. Is this cor- ‘ A.: It would be better if you used A409 in the first audio stage instead of B406, which is a power valve. ‘This, however, would not affect selectivity. CRHEN GRID" (Ngaio) : I have made the Loftin Four, but cannot work it well from the gramophone. When I switch over the set gives a steady slow beat and is unworkable. A.: This is due in all probability to pick-up on the gramophone leads. Try placing the pick-up in the cathode of the detector valve, that is, between the junction of the 50,000 ohms resistance and the connection to the 200 ohms potentiométer and the cathode itself. A switch eould be provided to short-circuit this eonnection. 2. When the set is tuned on 2YA and 2ZW there is a dead spot spreading over

about three points on the dial in each ease. It does not occur with outside stations. A.: It appears to be due to overloading the detector, and you can overcome it by using an aerial consisting of a piece of wire a few feet long. ¥.Z. (Wellington) : I have a "Trina- * dyne" set, described by "Cathode" some time ago, and I can just hear 2ZW. Would another valve give me more volume? A.: Yes, you would get much better rasults if you built up the cireuit desinging:

seribed by "Cathode" some time ago Une der the heading of the "Trinadyne Two." You could use the method of regenera tion employed in your present circuit, in other words, just add the extra valve as shown. You may have to wind a special coil to separate 2YA and 2ZW. This coil might well take the form of that described for the "Rejecta Il" crystal set. In fact it would not be a bad plan to incorporate the "Rejecta II." 2. I have a battery made up of three two-volt 20-ampere hour cells. The charging rate according to the label is 5 amps. I have access to a battery A CA TET OT OE ETE LA a en SS

am AS ~ ates ORRESPONDENTS must attach this coupon to all queries sent to the Technical HKditor (Box 1032, Wellington. Limit three plese letter ig accompanied by 1/ee, Name of set Ps eerescoesevessecsses Number of valves seccocccccccvccces F Name Poeeeacosesseesseesessoeasses ’ Address Soeceeeenocoaccoeseseaeses Cee eeeeeccesesesseesssceceesesceessed SSESEHEH SS SHHOSHSSESOSESESEH OOS ESO DOSER Nom de plume Saeeereseesescetese To be kept in subsequent inquiries. Date Seeeeeteseseseserevereren Please Note:(1) Be specific and brief, tabulating, if possible. (2) eT the oe ey: and on one side tt) e (3) We "not design circuits, but accept suggestions for feature articles. Solving trouble, as different from advice, is difficult by correspondence and while letters are given every consideration, answers are not necessarily correct--they are only our opinion based on the matter supplied, which may be quite inadequate. Intricate and involved specifications cannot be supplied without a specialist’s fee.

éhariee with tappings at 2 and 4 volts, amp. Which tapping should I use? A.: Connect the positive of the two batteries together and the negatives together and take a lead from the common positive and cummon negative to the two-volt tapping on your charger. HORTY" (Stratford)-How many grid and plates turns must be woun‘ om a valve base former to tune over the 80-metre band using 30 gauge, d.s.c. wire, and a .00001 midget condenser? A.: .00001 is a very small condenser to attempt to tune over this band, and you will find that you will have to break it into two coils to get complete coverage. . Try the following, grid coil 12 turns, reaction 11 turns, and grid 20 turns; reaction 18. OVER THE WAVES (Marlborough): What alterations should be made in

the Outspan coils using a .0003 differential condenser? ‘ ; Reduce the number of turns on the tickler coil by about 10 per cent. 2. Whe number of turns for the primary using 32 d.s.e.? A.: There is no need to alter the number of turns from those given in the "Radio Record.". . 3. The best valves to use in the four-volt series? : A.: A442, A415, A409, "PDADIO" (Wellington) : Reception has dropped back with me when it should have improved. The valves are only three months old. A.: Check up upon your batteries for voltage, your aerial and earth for good contacts. Undo the earth wire where it joins the pipe or whatever you use for an earth and serape it until it is clean and bright again. If you can,

let doivn the aerial and examine the wires and see that they are not corroded. Also examine your insulators and see that they are clean. ‘ 2. The aerial poles. are 85 feet at one énd and 38 at the other. Would it better to make both poles the same height? A.: Most certainly. 8. I can receive four Japs and 80 small stations: only with the help of a wavetrap,* which seems to add extra power to my set. A.: The wave-trap is tuning your aerial, and thus making your set more sensitive. X (Dunedin): Is a .000025 mfd. midget condenser too small for shortwave work? . A.: No, if you matched the coils to the condenser. 2. Would you design coils for the shortwave band, using 2in, former? ‘A.: We regret that we cannot do this, as if we design the coils for every purpose that we are asked we should be doing nothing else. 3. I was experimenting with the resist-ance-coupled amplifier and the grid leak resistance. I accidentally disconnected

the grid leak resistance and discovered that the set worked every bit as well. Can you explain why? ‘If it was in the plate circuit of the detector valve and there was no other possible chance of the plate current getting through, we cannot. Just examine it very carefully and make sure there was no alternate pass for the current. RY. DIO (Shannon) : In placing a shield round the s.c. valve, how far up the valve from the top must the shield eome?

A.: About half-way. ' 2. I have two phasatrols which I have taken to pieces, and wish to use the fixed condensers, What are the values of these? A.: .25 to .6 mfd. H C. (Christchurch): I wish to build * the P.C.J. 4, but would like to incorporate resistance reaction control instead of "condenser control. Is my diagram correct A.: Yes, that system would work quite ‘well, but probably an easier plan would be-to put -your resistance in series with the B-+- ‘to the detector, 2. What value resistance in ohms would be suitable for all-wave work? — A.: About 50,000 ohms. 3, What number of turns would be suitable for. the broadcast band using .00015 condenser? A.: You would need two coils, for one secondary 80 turns of 30 gauge enamel, with 30 turns for a tickler, 36 d.s.c.; for the other one’ you need 148 turns of 30 enamel, with 36 turns of 86 gauge (.s.c. for the tickler. ‘The secondaries for both radio and t.r.f. coils will be the same. The primary for the radio coil will be about 8 and 12 turns less than the respective ticklers,

K A.D. (Wellington): Are the new * circuits any better than the "Crystal and Valve," and if so which one? I have had 87 verified stations on this receiver, but since I have renewed my batteries oscillation has been very rough, On part of the dial it will not oscillate, while the remainder produces only a fierce squeak. A.: This sounds very like your valve; have it tested. If your set has been going well do not interfere with it, other than changing the valve, grid leak, or condensers. D*NAMO (Waitomo Caves): How can I add a radio frequency valve to my 8-valve set the circuit of which I. enclose? A.: We might have L.en able to have helped you had you sent us the theoretical diagram of your set, but a weird collection of lines leaves us quite bewildered. However, before very long we shall be adding a radio stage to the "Ran Two," and this should interest you. 7 2. I was.troubled with audio howl and placed a .0002 fixed condenser across G. and P, of the power valve. This stopped a little and gives me more volume. Am I doing any harm?-No. FUSE (Hamilton B.): I have a transformer marked P1, P2 and Si, 82. What do those. terminals indicate in. modern terminology ? A.: PI-B-+. P2-P, S1-F, S2-6. 2. Is the choke in the "Ranger Two" necessary, and could I use a fixed resistance instead? . A.: You may be able to work without the choke and use a resistance, but. the choke is preferable. : 8. Is one terminal on to the fixed plates and one on to the moying plates in a condenser or are both terminals on the fixed plates? A.: One terminal is for thé fixed plates and one for the moving. The moving plates are ‘connected together and toy earth. BROADOLA (Auckland): Can you give me the eoil data for P.C.J.4, using .0001 double spaced condenser for tuning and reaction coil wound on valve bases? A.: If you refer to the table as published in the "R.R." a short time ago and use the specifications for a 14in. diameter coil you will be about right. AM constructing the moving-coil speaker described in the "R.R." some time ago. Would if be suitable for my set ‘using a 201A in the last stage of the amplifier? A.: By not having a2 proper amplifier you will get no better results than if you

had an ordinary cone speaker. You need & power valve if not a power amplifier to get the best results from such a speakr. , 2. Can I use a trickle charger to energise the speaker field which is wound for a 6-volt supply? A.: Yes, but you will need to shunt an electrolytic condenser across the output of the charger, . 8. Will the wire taken from the primary of an ordinary transformer be suitable for winding the moving coils? .: If you use a step-down transformer the fine wire would be quite satisfactory. [TUPLEx (Blenheim) : Do you consider it worth while to have the superheterodyne receiver, illustrated in the accompanying magazine made up? A.: It is a good receiver, but we venture to say a better one will be described in our constructional columns before long. 2. Do you consider its distance-getting ility is greater than that of the stanmrd factory-built set? , A.: Most decidedly yes. . % Does it comply with the P. and T. regulations? A.: If you wind a separate and secondary for the aerial coil it will probably do so. It is just hard to say whether a circuit can be approved by merely looking at it. The set has to be tested in the P. and T. laboratory. V ©.T. (Wanganui): How many plates * of the size enclosed are necessary to make a .00005 and a .00015 condenser? A.: Por the .00005 use two moving and three fixed, for the .00015 use eight fixed and seven moving. They will be quite suitable for the "Advance" short-wave receiver in the "Radio Guide." T 0. (Invercargill): My aerial is 40 * feet high at one end and 25 at the other. I get a great deal of noise which is not apparent when using an indoor aerial or when the outside aerial is shortened to 60 feet. ' A.: It would seem that some of the joints are not satisfactory or that you are living in a locality where interference is bad and the shorter aerial minimises the pick-up. JK ELBURN (Wellington) : Would you let me know the number of turns for the broadcast coils of the Sellens short-wave reeciver? I am using valve base coils.

A.: You will need two coils, the first will have a secondary of 80 and a tickler of 80. . The next will have a secondary of 148 and a tickler of 65. These specifications apply to the detector eoil. The r.f. coil will have the same number of secondary turns as the detector, but the primary will be a few turns less than the secondary in each case. The wire is 80 gauge enamel for the secondary and 30 gauge d.s.c. for the secondary. 2. In the lay-out diagram the switch is shown between the plate of the first audio and the grid of the second audio.

The text differs from this. Which is corree A.: From the plate of the first audio to the grid of the second audio. POWER PHNTODH (Kauroa): In which issue of the "Radio. Record" were details of the Loftin Four published? A.: December 4, 1930. 2. Is it harmful to use a 232. type s.g. valve with zero grid bias?-No, 3. In a recent issue of the "Radio Record’ mention was made of a new pentode for portable and battery sets which had a very low "A" and "B" battery consumption. What type is this? A.: The new Philips B443. N#28010 VERUM (Cashmere): I intend to build the Loftin Four with 245 parallel valves, using a dynamic speaker with a 2500 ohms resistance. Where can this be used? A.: Substitute it for the 2500 resistance in the published circuit. 2. Can I use .00035 ganged condensers with matched shielded coils instead of those published ?-yYes. . . 3. What hum bucking condenser is used, .6 or 1 mfd.? 7 A.: Hither will do. " 4, Will I have to increase the secondary voltage to accommodate for a 2500 ohms field resistance? _ A.: No, not unless is used in a position other than that indicated in the text of the previous articles, | B G. (Nelson) : I have a five-valve neu- * trodyne set and wish to put another power valve. Do I have to put a gnothar "B" battery as well as a A.: It depends upon the amount of voltage you now have available. A power valve should be worked with a power of 135 volts, though 90 will do. It is really better to put in the extra block and bring your "O" battery up to that required by the manufacturers for the particular valve you install. RHO SIGMA (Ngaio): I have recently completed, according to the somewhat meagre specifications, in. the 1931 "Guide," the super het. shortwave adapter and it failed. I have had to guess at some of the components, A.: We publish herewith a diagram with full explanations, also a diagram of the layout. If you will follow the in- | structions given and get the components

eorrect you will get your set to function all right. 2. The broadeast set to which the adapter has to be connected has two sages of tuned r.f. Is this sufficient?es. 8. Must the return from L.5 be connected to any point of the set?-No. 4, Would increasing the number of turns on L4 cause the set to oscillate? A.: If correctly constructed it should oscillate with the number of turns given, but increasing the number of turns would certainly help oscillation.

F D.W. (Lower Hutt): Can I add a * stage of r.f. to the a.c. Night Hawk shown in the "Guide"? A.: If you intend using it for all-wave ‘work it is not advisable to do so. We hope at some future date to describe the Hlectric Night Hawk, also the Dlectric Kestrel, but we canot say anything definite ye , STUMP (Napier): I constructed the ~ Loftin Four and followed the instructo detail, but every time the condensers are brought into resonance the set oscillates. How can this be prevented? A.: By reducing the number of turns on the primary coils and r.f. chokes in the "B" leads to the screen grid valve. . 2, How many primary turns are required for a transformer using a stalloy core i 1-8in. x 1 3-16in., and what are the number of turns per volt? A.: Primary 1470 turns, of 26-gauge wire, turns per volt 64. L H.L, (Lower Hutt).-I would like * the specifications of a two-valve battery set. Oan you supply full particulars? A.: We shall do so very shortly when we describe the Ranger Three, H.G. (Oamarn).-Would one trans- * former and two r.c.c. stages deliver as much volume as two transformer stages ?--Yes, . 2. Would 7/18 aerial wire be any: improvement over 7/029?-As far as signal pick-up is concerned? A.: 7/18 being slightly large, then 7/22 (or 7/029) would theoretically be the better wire, but it is doubtful if there would be any appreciable difference be tween the two. ITEHARD (Seddonville)-Is the .. Sparrow Hawk Differential Adapter for my 5-valve set?-Yes. 4 Would I get good results with same. -Yes. 3. How much would it cost to build?about £8/10/-. E R.W. (Wellington).-My accumula- * tor has lately been bubbling, and acid has been escaping freely, Within 4 fortnight the liquid fell below the level of the plates. . Av: It seems that there is an short circuit, unless, of course, you are overcharging. Charge it fully and drain off the acid. Wash out with distilled

water. Refill with acid of the correct density (1125), and then recharge aud use. If che bubbling persists cake. the battery to a specialist. You must not drain off the liquid without fully cnarging.the accumulator, but once haying doue so you can leave the accumulator without liquid for some time. You wi quite safe for ten. days. SCREEN (Cambridge) Would you supply the following information relative to the power grid system of rectification: (a) The value of the condenser ; (b) the value of the grid leak; (c) apvroximate detector voltage; (d) connec¢tion.of the grid return. A.: Condenser, .0001 to .00015. (b) The grid leak, .15 to .25 megohms. (c) Detector voltage as high as possible. Anything from 135 volts up. (d) A grid return goes to A--. See the diagram reproduced herewith. 2. I have not had success by adding an s.g, valve. One appears to give me a lift no greater than that of an ordinary triode, whereas two are little better, and three very little improvement on the two. With one s.g. valve, oscillation is altogether absent, but with two or more it was so bad that I had to reduce the primary until there was little or no amplification in the system. The valves, ete., are fully shielded with aluminium. lieve inter-action is taking place between the plates and the grid of the sg, valve. A.: Oscillation appears to be taking place because of common leads or common resistances, and if you use plenty of by(Concluded on page 29.)

Questions and Answers

TA ROAR (Continued from page 1%)

pass condensers you ehould get over tom of the ‘primary amd "A> insert ° @ ry and insert a 006 condenser. Between the bottom of the secondary coil and the filament return there should be a bias battery, and across this put a fairly big condenser, say .5mfds. The bias should not be very high; about 14 volts would do splendidly. Check up your wiring for closed loops-filament wires that are a few inches apart which Tun parallel to one another, In general keep your plate and grid wires well apart, but with filament wires bunch them together, The judicious use of chokes in plates leads, and also in the screen leads,

if necessary, with adequate by pass condensers should enable you to overcome the trouble. 2. Could you give me a diagram of a tuned anode coupling for the first stage, also the value of the coupling condensers, e A.: Yes; we reproduce a suitable diagram on page 15. K.S. (Papakura).-What additional * apparatus would be necessary to change my set to all-wave? It is a det. two audio. . A.: It is not clear to us how your eoils are arranged. Where is the primary connected? Your best plan would be to take the det. andio stages from the Kestrel Three, for you have all the specifications for primary and_ tickler coils. You could bring the aerial into the grid of the secondary coil through 2 neutralise ing condenser. 2. What canses a blank spave on long: wave where there is no oscillation? A.: That is due to a dead spot which you ean shift by using a condenser in the aerial. It is due to peculiarity of your aerial or valve. pv2ZLeD (Timaru).-In a school magazine there is a descriptioy of a erystal set which is no more than a coil connected to a crystal and phones, The aerial comes in at the mid point of the coil, yet the writer states that he can get all N.Z. stations on it. How does he tune it? A.: It is tuned by altering the inductance by controlling the space between the numbers of turns on the coil. They are arranged on pieces of string, and you either extend the coil or contract it. Undoubtedly this way of tuning is a compromise, and is not 80 good as laying a fixed

coil with a condenser shunted across % It must be a very good set to get all N, stations, N. (Hamner Springs).-I have built * the D.C, eliminator from the "R.R." of October 30, and am using it with my set, but while it is giving good results as far ag smoothness and volume are concerned, stations lower than 3YA cause the set to oscillate, A.: We suggest reducing the voltage on the detector valve as coupling is takin place between this and the remainder the circuit. TT RICKLY CHARGDR (Wellington) : Part of a mains operated relay I°jn‘tend making (for automatic switcli¥g purposes) is a solenoid which is to function only for about 15 seconds each time the amplifier is switched on. An iron core is to be so arranged that when the mains current is switched on it will be drawn into the solenoid moving a distance of between 1 and 2 inches in 10 or 15 seconds (due to its operating a small train of clock wheels and governor), Then the circuit is automatically broken, The core is part of an old car sparking core, and consists of 24-gauge wire bound together. It is circular, about din, in diameter and 3in, to 4in. long. Could. you, sive me particulars of the solenoid to use A.: We would not attempt to estimate the size of solenoid necessary without knowing the magnetic condition of the core anl the exact load to be drawn in, So much depends on these factors. We would advise you to get into touch with a consulting electrical engineer, CuRious (Hawke’s Bay): My set emy" ~ ploys a full-wave rectifier, which, though it has been in operation only five months, lights blueish. A.: The valve has not been properly evacuated. There is. gas in the tube, an this is ionising when you turn on the current. So long as it functions it will be all right, but if you notice any defect in your set, such as volume falling off, you can attribute it to this cause. R W. (Wellington): How many turns * would be required for a valve base coil to tune the 600 metre band? A.: Valve base coils would not be suitable to tune this band, You would need a 3in. former, and upon this wind 200 turns of about No. 26 gauge d.s.c. wire, 2. What would the r.f. choke need to be wound on and how many turns are mere A fully described $ was y in the 1980 "Guide," and reproduced in "R.R." some time ago. As another qu tion nas been raised on the same subjéct we are reproducing again this piece about chokes, and trust it will be what +you are requiring. 3. What ratio a.f. transformer would be used in the 1st stage to give best results? A.: If you are using more than one audio stage, the ratio of the transformer should not exceed 84-1, If there 3s one stage only you could use a 5-1 or even a 7-1, but the use of high ratio transformers is fatal if there are more stages than one.

GPAN (Dunedin) ; I have built an Out- . span Five, and it is not giving any- \ thing like the result that it should. As soon as I bring the r.f. condensers into alignment a vicious rattle is set up. I have tried shielding the valves and the condensers, but there was no improvement. A.: If you have followed the lay-out exactly as it was given you should have no difficuity on the score of uncontrollable oscillation, We would suggest extra bypass condensers between B+ r.f, and earth and between the grid return and earth choke in the leads to the plates of the r.f. valve suitably by-passed would also help to control oscillation. Look for a defective condenser and defective valves. Test the coil for continuity, and try re versing the connection to the primary coil, 2. Would a choke in the screen-grid circuit be of any use? if so, how many turns would you suggest? _A.: A choke is not necessary unless the éreen is taken to a point common with ther leads to different parts of the set. ‘he choke could consist of a thousand "turns on a core former. A suitable choke was described in the 1980 "Radio Guide" and reproduced in the "R.R." a short time ago.. ( (©. (New Plymouth): My 4-valve Ke electric set has become very unstable, particularly on the lower wavelengths, A station may be tuned and then it completely fades away, and the set bursts into oscillation. It cannot be left unattended for any length of time. , A.: It requires to be reneutralised, or the instability may be due to the lack of by pass condensers. And then if there are plenty of by pass condensers, it is possible that some have broken down. Try fairly large condensers across the "B" batteries. We presume that you have them between the plate and earth. ~ Mike (Blenheim): I have recently ac4a quired from the estate of a deceased * person a partially complete radio set. Unfortunateiy the circuit diagram cannot be found, and all the parts are Hnglish. Could you give me a suitable cireuit? A.: It appears difficult with the information given, to give you the circuit you require: We have hunted up several English magazines, but cannot get anything quite suitable. We would suggest that you write to a city dealer who specialises in Bnglish products, and see if you can vat 9 suitable circuit from them.

2. Can you tell me the correct connection for the respective 6-pin coil bases? . A.: The six-pin: base may be used in a variety of ways, depending upon the circuit employed. A quite usual system seems to be (1) aerial, (2) earth, (3) earth (bot. sec.), (4) grid, (5) wavelength change, being the centre tap of the secondary coil. This could be used for regeneration, but, as we added before, there are an infinite variety of ways in which the six-pin coil can be used. agcour best plan is to scan through the in this issue and see which ealers specialise in English goods, and drop them a line. They possibly will be able to do something for you.

N2w SET (Dunedin): I have a T75ft. aerial, including lead-in, and am very close to a high-powered electric cable. Would reception be better if I lengthened it? A.: It certainly would, but by lengthening’ it you are liable to pick up interference from the main line. 2. I am not troubled with much noise from the local station, but yet consistent crackling absolutely kills reception when volume is turned on to bring in the Australian or long-distance stations. A.: Remove your aerial and then turn up your set and see if the noise persists. If it does not, as we think it will not, then you can take it for granted that the noise is coming from the power lines close by, and in this case the only plan left open for you is to get in touch with the District Radio Inspector, who should be able to help you.

8. What height should my aerial be -to give satisfactory receptions from distant stations? A.: As high as possible, particularly if you get interference from power lines; 40ft, is not too high. RB L. (Christchurch).-My set is a * home-conducted all-electric receiver using 2 RF 227’s grid detector, 227 and reaction. My difficulty is in the primary, but I have tried 60 turns of 34 s.w.g. enamelled wire solenoid wound over the secondary, and tapped at 30 for split primary neutralisation. Results have so far been only fair, with selectivity poor. I have tried several types of primaries, but found the one mentioned the best, although it is nut satisfactory. The second tuning condenser has littie or no effect apon the signals. : It is quite clear that there is something wrong with the second r.f. stage. We cannot help you by pointing out what it is, but concentrate on that stage. Until that condenser tunes sharply there is still something wrong which is affecting the set generally. We think if you get to the botiom of this trouble your selectivity problems will disappear. You seem to be using the correct number of turns and the best system of coupling the valves. We presume that you have taken the yery simple precaution of arranging the windings in the same direction,

G L.H. (Northland): I have assembled ° the Rejecta Set and am pericetiy satisfied with the resuit, but is it not possible to get greater strengta from 22 VV? We get 2YA strongly enough to drive a speaker, A,: 2ZW is a relatively ‘weak station, and it is not always possible to pick it up on a erystal set. The Rejecta is equally as sensitive as any other type of crystal set, as made evident by the fact that you ean receive 2YA loudly enough for a loudspeaker. You should, however, be able to receive 2ZW at fair crystal strength. Of course, you will never be able to get it really well on account of its low power.

C "B. (Auckland): Can an "A" and » ©" eliminator be made with only one rectifier, preferably a Westinghouse, and if so where can I obtain instructions for same? A.: An "A" and "B" eliminator can rarely be made with the same rectifier, unless it uses the special rectifying valve for that purpose. A suitable circuit -was described in thé 1930 "Radio Guide." We do not know of a Westinghouse rectifier that will do both jobs, although you could get two Westinghouse rectifiers, one for the "A" and one for the "B." 2, Would the Radiogram Five work satisfactorily with an ordinary valve instead of a s.g. for the r.f. stage? If so, can. you supply the circuit? A.: Yes, it would work perfectly well with a triode, stage used in the rf. A circuit is not available at the present time although in the near future we hope to bring out a three-valvye circuit with a triode in the first stage. You could, however, build the Browning Drake with two stages of triode r.f. This would be the Radiogram Five, only the battery version. You would, of course, adapt pushpull amplification, as shown in the "Radio Guide." 3. Is a s.g. valve much harder on batteries than an ordinary valve? A.: No, It requires very little extra current. 4. Is a Philips A635 valve suitable for the first stage of r.f, amplification? A,: The A635 is a very high impedance triode, and is very difficult to neutralise. in a circuit such as the Radiogram. A far better plan would be to put in a modern s.g. valve. 5, In my set I am using a .0005 tuning condenser, and cannot tune below 300 metres. Can I lower this by taking a few turns off the secondary? A.: Nes. Dake off about 6 or 10 turns,