Questions and Answers

Radio Record, Volume V, Issue 6, 21 August 1931, Page 13

Questions and Answers

(CABBAGE (Gisborne) writes concerning our instructions for fitting headphones to an electric set. "I have had phones fitted to my eight-valve a.c. set, but find them unscuccessful. One cannot pick up the distant stations any better than he can on the loudspeaker. I would not advise anyone to fit phones to af electric set. I have taken mine off." In\veply to this, we would remark that we are in agreement with our correspondent. If you cannot pick up the station on the speaker you ‘would have very little chance of picking it up on the phones, for the simple reason that the noise will be magnified out of proportion. However, phones can often be fitted to an electric set to make listening more comfortable and convenient. ‘Thus, if you wish to listen to the set at some, distance from it, you can run a relay line and use the phone only, or, if you are sitting u late at night, and do not want to distur the house, the phones can be used with the volume turned down. Phones haye very many more uses than for merely winking nn distant stations.

SSeS Oe -"=i-_ets Al R.W. (Roxburgh).-I have built the ° Knife Edge Rejecta," but cannot separate KIF1 from 4YA. The two stations hererodyne. Similarly I cannot wegpliminate 4RK in fayour of 1YA. ey A : We are afraid that the best built avetrap will not operate stations that Are close enough to heterodyne. See our article in last week’s issue. . 2. I could not procure d.c.c. wire, so | used d.s.c. Would this make any difference ?-No. 8. How could I employ the parts I now have to rectify the trouble ‘A.: We are afraid you cannot do anything to improve matters. A wavetrap will restrict a broad station to something like its proper frequency, but it will certainly not help heterodyning stations.

They heterodyne before they get to your set, so to speak, so that the wavetrap does not really get much of a chance. DECIBEL: (Masterton): I enclose a sketch of my set. ‘The voltages seem uduly high. Is this so? A.: The voltages are fairly high. It almost seems as though a resistance has broken down. The average modern valve will take a high voltage on the plate, but 215 on the plate of the screengrid valve is rather too high, and it would be as well to check through the resistances in the main chain, and, if, these appear to be all right, put in a resistance between the high tension supply and the common plate lead. The voltage on the 945’s is about right, although the valves are not balanced properly. which accounts for the difference in grid-bias. The differ. ence in grid-bias may be due to the valves or the biasing resistances being different 2. The detector and first audio resistances are the same colour. How would a difference of 15 volts on the plate be ac-

counted for? A.: By two facts. The detector passes more current, and consequently the resistance, which we are presuming to be the same as that in the first audio, will break down the voltage to a greater extent. The action of unrectified current on the grid of the valve has a further effect in tending toward an inereased nlate current, and. whatever increases the current. lowers the voltage. We presume you have changed the detector and first audio valve, so that the difference is not due to the valyes_themselves. ; 8. What current passes in the resistances marked A.: It is impossible to say. You would need to know the drain between "A" and earth. This is the bleeder current. You would have.to place a Williameter be-

tween the X resistance and earth and und ot the current, then, knowing the voltage dropped, you could calculate the resistance. Undoubtedly, in working gut your voltages, you forgot to allow for the bleeder current, and this may be in the vicinity of15 mamps. Inealeulating resistances and current, where bleeder resistances are used, you must always add in the bleeder current. Thus, if the screens must be supplied with 14 mamps., and the next resistance "own is a bleeder to earth, and passes 15 mamps., a total of 16% will flow through both resistances, and _ this, of course, will have a very big effect unon the voltage. HLBR2 (Herekino).-1. What constitutes a by-pass condenser? . A.: See the "Diagnosis of about_a month back. . Would results be as good, out the .006 condensers when using a sixyolts accumulator and "B" batteries 10 the "Sellens’ Shortwave Set?’ A.: That is more than we can say. They prevented instability in the original model. You may find that it will go just as well without it. In amy_case, try. , 8. What are the different "B" A.: The "B" voltages really depend upon what you are Willing to place upon the valves. "B" 4 and "B" 5 could quite well be joined together, and might be of the highest voltage aydilable, say 125 volts. ."B" 3, 223 approximately, "PR" 2 might again be 90 or even 185, and "RB" 1 half of "B" 2. . 4. I use A615 and A609 in H.R. 4, Would they do for detector and second audio stages of the "Sellens?-Xes,

_5. Is it necessary to shield when one lives far from interference? — A.: Yes, The shielding is not against local interference, but against self-oscilla-tion. 6. Could .00014 condenser, not a double space, be used instead of a .0001? A.: It could be used, but it will throw out your tuning. You could reduce its eapacity to a 0001 by using in series a condenser of a capacity of . . 7. I am still battling with R. the W. detector circuit, as an adapter. I am getting plenty of Morse and ‘some stations. What distance apart should secondary and tickler be? A.: You must try them to see where the optimum coupling is, They should be fairly close. y 8. Are my valves right, A615, A609?9, I find I get better results with rf. valve removed from the set, A.: This is sometimes the case. it toices a load off the battery, and to some

extent prevents back Ccoup*l Mn. 10. I enclose a sample of wire. I used 100 turns jumble wound. Is it satisfactory for this purpose, and if so, what 18 the size? ‘A.: It is fairly coarse for the r.f, choke, the diameter being 30 s.w.g. dct. J P. (Dunedin): Could you supply in- ° formation regarding a set of coils for the Outspan Five, in order that I may make it into a six-valve set? A.: For the three r.f. stages you will make three coils identical, that is, serial coil and first and second radio, ‘These will be as follows :--Sec. turns, 80; 26 d.s.c.3 primary turns, ; 84 ds.c,, wound as described in the "RR." 4th coil: Sec. turns, 80; 26 dis.c.; primary turns, 25; 34 d.s.c.; tickler, 30 turns, 39 ds.c, We think to start with you had ---s

better make ali the COMUS Wile Lie new", number of turns on the secondary, and then remove turns if necessary, to match. 2. What coil alterations will be necessary to use Philips A630 valve in the r.f. stage in a four-valve Browning Drake? A.: You may have to.do some exper! menting to use this valve in the first stage. Generally it is necessary to double the number of turns on the primary coil. 3. Could you give me a diagram of connections showing how to add further sg. rf. stage to the Outspan Five? ‘A.: We are not particularly keen on supplying diagrams. The third r.f, stage is merely a duplicate of the first. However if you cannot manage it, send us 4 stamped and addressed envelope and we shall sketch out a diagram for you. Dx*8rw. (Wellington): Is it possible to convert a locally-made all-electric local station receiver into one capable of getting distant stations? A.: We think it most inadvisable to attempt any alterations to this get. The most serious drawback is the power pack, which is built to supply exactly the current required and no more. W B.O. (Masterton) : What valves are * used in the Radiogram Five battery set in the "Radio Guide’? Would the 222 type be satisfactory in the r.f, stage’? A.: Yes, 222 would be quite satisfactory. The wiring is like this. The grid is at the top of the valve and consequently the wire that now goes to the grid terminal in the present layout must come to the top of the valve. The connection

to the coil and fixed plates of the tuning condenser will likewise come from the top of the valve. The spare "G". terminal takes the wire that now goes to the "py terminal. The "P.T." terminal now left free has connected with it the plate wire which goes through into the next stage. In other words, the grid is at the top of the. valve, the plate prong connected with the plate of the valve, and grid prongs with the screening grid. power (Otago).-I have a commercial eight-valve_ receiver less than three months old. When running round the dial from 100 to about, 80, with full volume, there is a loud plopping noise, accompanied by whistling and squealing when static is bad. A.: The set is oscillating, and it appears that you will have to get in touch with the agents who sold you the set so that it may be overhauled properly. jt. would be unwise for us to advise you ty. tamper with commercially-made receivers. As a matter of fact, the writer has encountered a somewhat similar trouble and it has been traced to a defective volume control or resistances. 2, Would noises from power leaks occur all over the dial or only at eertain fre--quencies? Gyre A.: It would depend upon how severe . they are. The possibilities are that they. \- would be all over the dial. We think that." much of the noise is due to your set being out of order. a

C H.W. (Iinvereargill): I have eon- » ¢ ‘structed the Sharman Receiver — from a recent feature in the "Radio Record," and the results were splendid, My log includes the Dunedin stations, 3XA, 2YA, and 2BL. I eould not hear anything until I shorted out the condenser in series with the crystal, although the receiver could be heard oscillating gently when a semi-permanent erystal was used. A.: The set usually goes better with the condenser, which is used to control the flow of h.f. current _to the erystal and so provide reaction. However, if it :4s: ws

(CORRESPONDENTS must attach this coupon to all queries sent to the Technical Bditor (Rox 1082. Wellington, Limit three questions, unless letter is accompanied by 1/ee. Name of set ..... ccescccccccencees Number of valves .covcccoceececarce Name cece ere coe eoOeGOG9OO00 00808 eo ceecccconesceccsececaccess ° COOH EHSSOAISSHSSSASSHHOHHGSOHDED Nom de plume eceeeescesesoeeoeas To be kept in subsequent inquiries. Date neecceceaccnenegneceesupe Please Note:(1) Be specific and brief, tabulating, if possible. (2) Write legibly. and on one side of the paper. (83) We do 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 in adequate, Intricate and nvolyed specifications cannot be supplied without a specialist’s fee.

os going better without it your set is not taking. harm. ’ 2, The stations on the lower wavelength came in when the tuning condenser was at its: maximum capacity and vice versa on the higher wavelengths, while the reaction condenser seemed to have no effect whatever. A.: Do you mean that the set will not oscillate when that condenser is taken out of the circuit? If so try a few more turns on the reaction coil, and if possible change your erystal. The trouble, however, seems to be in the condenser, as it is very critical. As remarked in the article you need a very small capacity, and this is difficult to obtain. 3. Would it be possible to describe at some later date an r.f. stage’for this re ceiver? ,A.: We will not promise to bring out @ extra. valve, as, after all, the set is only an experimental one. You could use the hook-up with an ordinary rf. circuit, such as that to be described for the "Ranger Three." > W.F. (Christchurch): The subject ** of pick-up adjustment is a rather

po long one and we refer you to the "Radio Guide," 1931, where the subject has been dealt with very fully. You are right in deciding that axis AB must make @ tangent to the circle, particularly near the centre of the record. Shorten your pickup until you get it near the ideal, but dook up the "Guide’-that will help you greatly. : ((OUNTERPOISE (Feilding).-Which is the most economical method of running the "Night Hawk" Two, dry: bat teries or accumulators? A.: That would depend upon the valves. If you use the .06 filament consumption type, then the dry batteries are the better. It is advisable to make a bank in series-parallel, 2. How long would the dry batteries last, using a 230 type valve? A.: That we cannot answer for you. Probably three months or -more, depend:+ ing upon the length of time you use it. . Is the set an efficient one-valve set on shortwave? A.: Yet, it is quite efficient. L P.H. (Dunedin): Ihave recently * bought a six-valve battery set’ and would like to know if my valves are cor-

rect, The first radio A609, 2nd Cossor vale, 8rd R.C.A, 201A, the detector, a "Paason, first audio 201A, second audio A.: Your first valve is right, but your .second we cannot say because you have -not given us what type of Cossor. There "are: about half a dozen of them. ‘The third one is correct, but with the detector Again we cannot help you. It should be either a 201A or a 221. The first audio is correct, the second audio should be a power valve of the 605 type. You will ‘find that best. results will be obtained by using R.C.A.’s 221 in all stages except the last, where you use a B608 type valve biased with about 15 volts-that is if you are using 90 to 100 volts on the plate. . 2. What are the capabilities of the set, and ‘is it a good one for DX competition? A.: The set is quite a standard model and will’ give you good results. You should be able to collect quite a good log for the DX competition, N2GATIVE (Canterbury) : I have just renewed my valves with 201A’s, but the "A" battery which used to last five weeks now lasts 10 days. Is this the fault of the valves? _ A.: You are putting a tremendous load upon it. Still, if your accumulator is good, it should last far longer than 10 days. Better’ send it to your battery house and ask them to test it for you. 2. Is my aerial, 55 feet by 20 feet passing partly over a roof, better than one, 20 feet by 18 feet? A.: Hver so much depends upon the situation of the latter; probably there will be little difference, L T. (Luston): I have decided to build * an eliminator, Could a vibrator battery charger be employed in a battery eliminator? A,: You could use the transformer ani! the type of rectifier is dependent wou whether it is full or half-wave rectification, If it is a full-wave type, you can employ the 289. type valve, or for halfwave, a 280 type with the plate and grid connected together. You can compute voltage, etc., knowing the output of the various terminals, which are generally tappings of the main secondary coil. You will use the maximum voltage by taking out any resistances that are in the vibrator charger, and ‘connect this in the approved full-wave style, or half-wave, as the case may be. For the "A" battery eliminator we suggest 1010 rectifier. 2. I take it I will require another winding for the filament? A.: Yes, although you could use the Raytheon type of valve which does not have a filament. It is a full-wave rectifier, and unless you have a centre tapping in your transformer, you cannot use it. You can put on a filament winding quite easily, only an a.c, voltmeter would be needed to measure the output. You will have difficulty’in computing the number of turns: per volt without dismantling your transformer. Twin (Auckland): I am intending to make a full-wave crystal set.. Could you please supply me with a diagram or let me know where I could obtain one? A.: A diagram was published in these columns a week or so ago, and you could and fall information in the 1929 "Radio suide.’ ISTENER-IN. (Alfredton): Would the jolting that an "A" battery, through being carried at the back of a service car for over 30 miles, harm the battery? : A.: It is quite possible. If the road were rough the plates would become damaged. Your best plan in a case like this is ‘to use a car battery, not a radio battery... These are more robust, and are better suited for the rough treatment, 2. I find my "B" batteries‘ run down wery quickly. . A.: This. is. possibly due to a brokendown: by-pass condenser, aged ‘yalyes, a short’ circuit somewhere in the set, un-

if this is correct, shut off the "A" suph from your battery. Now take off "Band flick it against the terminal. See if there is a spark, and if there is you have a short-circuit somewhere in the set, You -must take it down and pull out the offending part. If your set is as old as-you say, you may be sure that it is a brokeudown by-pass condenser. Sometimes dust between the moving and fixed vanes of the condenser. will cause a battery to run down, but:this would cause .a certain amount of crackling when you are tuning your set. WY MA. (Taranaki): Where could I obtain a circuit for my _ five-valve "Natcla" battery set? : A.: The Natcla Radio Company, Leinster Chambers, Grey Street, Wellington. T ©. (Auckland): Sorry, O.M., but we do not happen. to have either vf those two issues. If we.can locate them for you, however, we: shall send them along. . W BL. (Auckland): I have built fhd * "Night Hawk Two," adding a stage of audio and a.f. amplification. The tuning is very broad. How can I sharpen it? A.: You will find that the tuning on any set, such as this, will be extremely broad. Your only hope of sharpening it up is by the use of a wavetrap. F{CONOMIC Three (Gisborne): I- was greatly disappointed with the "Kesirel Three," for I thought it would be an ordinary r.f. in the first stage. However, at some later date I hope you will oblige with a description of the ordinary triode r.f. stage. A.: The triode rf. stage is- quite out of date. Not only is it less sensitive than the ‘screen grid valve, but there is the difficulty of neutralisation. However, we shall, in the-near future, be describing a three-valve set with one stage of cu Yr biased valves, Check up grid bias, we ¥ anced r.f., and this should meet with you approval, ‘ . . ( R420 (Tokomaru Bay) : What capacity of fixed variable condenser would I require when building a wayetrap to separate 2ZW and 1ZR? A.: You should use two formodensers, as you will need a very nice adjustment of capacity. , . D*23w (Masterton) : I operate a fivevalve commercial set, but the two original transformers have burnt out. What make do you advise for replacement? -A.: We cannot undertake to recommend any definite make. Your best plan would be to use one of the better-known types. Ask any reliable dealer, L A.A. (Kilinshy): I am intending to " alter my grid leak detector circuit . to power grid detection followed by r.c.c. amplification, but: have not sufficient confidence to make it up from from the sketch on page 33 of the "Radio Guide." Will you kindly -mark the alteration fr) the accompanying sketch. ed A:: In the first place; we donot advise you to interfere with your, present set. Changing over a commercial set is always a difficult proposition. Secondly. we do not undertake to answer queries such as this. In any case, it was a postal one, and should have been accompanied by a fee, UNCERTAIN (Christchurch): I am intending to make the ‘Kestrel Three," but wish:-to use an aluminium panel ag base. ‘Phis means that «the moving plates of the condensers and the arm of the rheostat-are earthed. How can I overcome this? ; rom A.: By regarding the aluminium as a negative, The moving. vanes 6 the r.f. three and differential condensers Will be connected’ to. A-, which is as in the circuit. The rheostat and the det. condenser presents a problem. The best plan is to insulate the moving Vane and leave the wiring as it is at present, other--

Po | wise you would have to redesign the set completely. . a ~ 2. Will you be publishing an a.c. verion of the "Kestrel Three" in the near future? A.: We cannot make any promises, but we hope to be able to do so. . "MAYRURO" (Auckland) : I have a three- ™ valve s.g, battery set, and have up 20 New Zealand stations and 7 Australians, but I cannot separate the stations that come in on the lower part of the dial. Could the set be made more selective. A.: First try the effect of a .0003 variable condenser in the aerial lead, or better than this a formodenser, which is semi-variable. Next try a wavetrap. 2. When my wavetrap is on I find distant stations come in with greater volume. How is-that? A.: Because you are tuning the aerial. This sometimes happens. 8. Would it be possible to increase the length of the aerial?-Yes, but you may interfere with selectivity. . , 4, Ig it possible to attach headphones te’ the set for short-wave stations that are ening through weakly on the speaker? A.: Yes, see the article in last week’s ¢ ‘eonstructional columns. 5. Short-wave coils on the set are from 24-90 metres, Is there anything of interest outside this band? A.: There are a few stations below it, but nothing worth worrying about. 6. Short-wave stations are listed in metres. How ean J find the approximate position on my dial? A.: See the reply to N.C, (Masterton) last week. %. Is the DX Club for short-wavers or broadcasters? A.: For both, although the DX Club primarily eaters for broadcast listeners and the Short-wave Club for short-wavers. Still, there is a considerable amount of overlap in both elubs.

8. What are the qualifications needed before one can become a transmitter? A.: Briefly they must understand the fundamentals of electricity and radio, and pass an examination set by the Government. They must know the Morse code and the laws pertaining to amateur transmitters, ‘They must show the examiners that they have a thorough understanding of transmitters as applied to amateur radio transmitting. 9. Is transmitting an expensive hobby? A.: Fairly, though a "ham" makes most ‘of his own gear and for this reason it is not expensive, It is certainly a very fateresting and instructive hobby. D C.D. (Auckland): Your query is * really ont e the scope of Questions and Answers. We do not. undertake to design amplifiers or sets. You can work out the value of the main chain of resistances in the Loftin White Amplifier -in this fashion. You know the current passed by the valves and this will of course, pass through the main chain of resistances, You know the voltage that the

valve requires to operate it at maximum, and that a further 200 volts is necessary to provide bias and the plate voltage for the detector, That means a total of approximately 450 volts to work on, and subtracting the 250 from this (as this is dropped through the valve itself), we find that 200 volts are left. Now if these 200 volts are dropped through the resistances comprising the main chain of resistances and the plate current, taken by the valves represents the amount of current flow, you can easily find out the number of ohms the resistances ‘must contain. So that R5, 6 and 7 can easily be arrived at. The bias also can be worked out, but this is a little more complicated, and the best plan is to try different grid leaks until you happen across the right one. The other resistances should be about right. 2. What output transformer will I need to match my American Ferrand Green Spot inductor dynamic? tito. 3. I find that no home-made scratch filter can approach the one used in the gos theatres when playing records. Why is this?

Ao? Because the people who made the talkies know more about radio and scratch filters than the people who make the home-built apparatus. A commercial product always attains a higher standard | than amateur built, for the simple reason that they have more resources to draw upon. oy WAAC (Christchurch): Can the "Sparrow Hawk" differential adapter be used for an a.c. set? .: Yes, if you build up the one shown on page 111 of the 1931 "Guide," it will be satisfactory. However, for an a. ‘set why not use the super heterodyne type also described in the "Guide’? If you use the ordinary type of adapter you plug in to the detector socket, but, of course, you must insulate the socket from tle adapter as shown on the same page of the "Radio Guide." G B. BOY (Dunedin): We think theve ® would be very little difference in the two makes of valve you mention. Certainly not worth making any changes if the valves have not lost their emission, If you wish to use Radiotron valves, use the new 221 type in preference to 201A. F, J.D. (Albury): I have a rechargeable "B" battery which is about 3 years old and seems to be losing its capacity for holding its charge. What is the cause? A.: The age of the battery. When an accumulator is three years old it is time it was discarded. However, if it is taken down, al] the electrolyte drained: off and refilled with sulphuric acid of the correct density (1.250) it may Pos. sibly hold out a little while It you are anywhere near a battery-charg-Ing depot or a garage with a electrician, we advise you to take it along: to them. If you do attempt to take down the battery yourself, see that you (Coneluded on page 28.)

Super-Heterodyne Coils © Several correspondents have asked for coil data for the a.e, screengrid super-heterodyne converter described in the 1931 "Radio Guide." We give them herewith:-

The wire gauges are given in small figures, and it is assumed that coils of the.same diameter as valve bases will be used. The windings will be approximately correct whether the coil covering is cotton or silk. The 10-meter coil should be spaced Zin. between turns, All coils have about ain, between windings.

Questions and Answers ee (Continued from page 15.) give it a strong charge before you do anything, ‘To take a battery down uncharged is fatal. M Z,M. (Lower Hutt): I have a five- * valve battery set and would like to know if it would be worth while fitting an eliminator to do away wit. Pihe "R" battery? If so, what is a reliable make? A.: For the five-valve battery set you peed an eliminator that will give you about 150 volts and 20 or 25 mamps. There are several well-known makes now available and we noticed some advertisea in the "R.R." recently. However, there are many good makes to choose from. Just make certain that you get 150 volis and 25 or 30 mamps. It will certainly improve your set a great deal. MA&SITE (Te Aroha): I have built a five-valve all-electric set and wish to develop it into something more advanced in design as I think pretty well mastered this circuit, which is three s.g., one 209 and one C443. I have been thinking of tackling a super het. of the modern all-electric type and would like to know the following :-- 1, Do the modern sets use the sai type of intermediate coupling transformers as the older circuits? 1 think I can obtain a set of these fairly cheaply. A.: More or less, but we would advise you to wait for a little while, say a month, until the design of our new a.c; super heterodyne comes out.

Band. 80-meter ... 40-meter ... 20-meter ... 10-meter ... 7 (30) 4 (80) 2 (20) 1 (28) Lt 37 (80) 16 @4) 7 (24) 3 (22) L2 30 (30) 13 (24) 6 @4) 24.(22) L$ 20 (80) 10 80) 6 (80) 3 (28) LA 5 (80) 3 (30) 2 (30) 1 (28)