Questions and Answers

Radio Record, Volume IV, Issue 47, 5 June 1931, Page 13

Questions and Answers

H M.B. (Taikorea): The wire is 26 * dee. PNQUIRER (Westport): What nunber of turns will be necessary on primary, secondary and tickler with a 3in. former to tune the broadcast band with a .0001 condenser. Reaction is from 00025. I shall be using 24 d,c.c. wire. A.: From 300 to 500 metres you wiil need 150 turns on the secondary and 50 on each reaction and primary. or the lower coil you will need 60 on the secondary, 25 on the tickler and 20 on the primary. X (Whangarei) ; Could I use a UX240 in place of the UX200A valve in the detector stage of the B.D. r.e.c. coupled amplifier? . A.: No, the valve is of the high resistance type and unsuitable for circuits such as the B.D. It could be used in one of the r.c.c. stages though a modern general purpose would be the safer. 2. After replacing the rectifying valve in my eliminator I find that the voltage has increased.. What valve should I replace the one already in use with to deerease the voltage? Aw: It is not a case of using another valve but inserting a resistance in the jJeads the voltages of which are too high. , Vv R.H. (Auckland): I have noticed the % * appearance of new Radiotron valves 221 and 280. Can you supply the charatteristics of these? A.: The 221 is a general purpose valve drawing .06 amps at 6 yolts on the filament, The detector voltage is between 20 and 50, but the maximum is 180 volts applicable in the case of a valve used as an amplifier, The bias voltages range between 4.5 and 10,5. It has an am. plification factor of 9 and impedance of 9000 ohms and costs 18/6. ‘This valve has recently been reduced from 20/-. The 230 valve is a general purpose one which works from a dry battery or an air coil. Three volts filament are needed at which tension .06 of an amp. is drawn. ‘The detector voltage is 45 and the maximum 90. The "C" battery is 4.5, amplification factor 8.8, impedance 12,500 and the price 18/-. 2. Could you name for me a cheap book that deals with the relation that the outside circuit has to the valve? .: The 1931 "Radio Guide" hag quite a great deal to say on this subject, particularly in Chapter 2. You would find further information in "The Magie Carpet," by Ralph Stranger, or No. 10 of Ralph Stranger’s Wireless Library. CREEN-GRID (Dunedin): [I have a four-valye B.D. which I want te alee into s.g. How would I go about it A.: The modern B.D. is the "Outspan Vive" published about’ a couple of months ago in the "R.R." You will find there full particulars. A H. (Tokomaru Bay): How do the * following valves compare with regard to "A" ond "B" battery current: The 201A and the 221? 4 A.: So far as filament current is con\corned the 221 is much more economical. BS. requires only .06 amps. against the .25 required by the 2014 As far as plate current is concerned the 221 is still alightly more economical.

2. I find that by putting two of these new, valves in first and second audio stages reception and volume are improved a great deal. I was told, however, that they are much heavier on batteries. A.: Your information is erroneous, as the statement given im answer to your question shows. kK SHT (Waipukurau).-My valves have completed approximately 1500 hours. Would you advise a removal. A.: Not unless reception has noticeably fallen off. Do not renew valves until results tell you they should be removed. 2.In view of recent valve improvements would you give me the numbers and makes nipat suitable for my three-valye battery se

A.: Those supplied cannot be bettered, although they may be some twelve months old there are not any new ones to take their place. The general practice for manufacturers is to improve each valve without altering its name, so that you will probably find that your next set, providing that the valves are new and have not been in stock for a long time, will be better than the original. ‘The valves are improved generally by reducing their "BY" battery by consumption, increasing the slope, and diminishing the impedance, If you want 2-volt valves, you could, course, use the aew 230 and 231 type valves. 8. I have a 4-volt accumulator on hand. Would you advise the use of 4-volt valves instead of 2?-Yes, they will probably give you improved results, and seeing they will not cost you any more it will be as well to make the change. 4, I use a horn speaker. Speech is good, but musie lacks tone. Could you give me the name and number of a unit and chassis that I could mount on a 5-ply board? A.: The fact that speech is good and that musie lacks tone is not. uncommon with horn speakers. A suitable speaker for your set would be the 66R chassis and unl 5. If I place my finger on the fixed vanes of the volume control condense the volume increases, Is that in order? A.: That is due to your bringing the set wearer eaciligtion, and is gq

order, providing, of course, there is no other complicating factor. 6. Is the life of "B" battery shortened when two speakers are used? . : A.: There is no extra drain on the batery. . R S.N. (Hastings).-Are any of the * Jongwaye stations audible in this country? A.: While we cannot say for certain, it is most improbable thut any of them could be picked up. If any reader receives any of them, we should be glad to hear from him. 2. In which issue of the "R.R." is the article by "Hard Up," describing the Daniell cell? enahenmmans

A,: The first article by "Hard-Dp" a): peared June 6, and this was followed by : more detailed description in our issue oi November 7. 3. I find my set develops a squeal when the plug is inserted in the second audio jack I put a .002 condenser from the grid terminal of the second transformer to the "OQ" battery. Is this all right, and will it hurt anything? A.: Actually you are by-passing the squeal. It certainly will not harm anythine, but surely it will weaken your reception slightly and take away much of the high frequency reproduction. Probably the better plan would be to reverse the connections to the primary of the second audio transformer. >

Pp eC te TP\RANSMITTER (Kerepeehi) : Which -. im your opinion is the best s.w, receiver, "The Sellens," the "Kestrel," or the "Advance" a.c.? A.: The "Advance" a.e, and the "Sellens" are very much on a par, but one of course is a.c. The "Kestrel" is a muc. weaker set than either, but will give exeellent results. . . Can’ you supply a diagram the wiring of an extra s,g, stage for the ‘Radiogram: Five? . A.: At this stage, no. a few weeks we shall bring out an extra stage for the Radiogram Five. (CKuOKE (Feilding) : Can I use a power valve in the last stage of my_set without using an output transformer? A.: Providing the power valve does not draw more than 8 mas., as you say, it would be quite safe to pass this current through the speaker. 2, 1 intend to make a B eliminator, incorporating two chokes of the tyne set watt in the table of the "Radio Guide." (an I wind these chokes, using 36 wire instead of 34, without affecting the inductanee seriously? A.: Yes, providing you will not be wanting more than 50 mas. the chokes will be improved by using 36 wire instead of 34, as you are increasing the batteries. 3. Will the reduction in the size of the window affect the inductance? A.: Not to any extent. UBSTION MARK (Wellington): Ex--perimenting with an L.W. amplifier I. have no success in picking up the local 80-meter hams. With an _ ordinary broadeast coil and the plates of the condenser all-out one of these amateurs came in fairly well. so 1 wound a smaller coil, put although I varied the number of turns from 5 to 20 I could not get good results, although I received an 81-metre ham in the middle of the condenser setting. added a erystal, and this brought the volume of the short-wave station about level with an ordinary broadcast coil, but definitely no louder. 3 5 condenser is too large for use in conjunction with a small coil for the short waves. You consequently cannot tune finely. We have not experimented with the L.W. on _shortwaves, and consequently cannot help you to a great extent. We do not know of anyone who has. We should be pleased to hear more from you in this respect. 2, Why will an electrical rectifier jar not form up? The solution is about 120z. of distilled water and half a pound of -ammonium phosphate for forming; I connected the jar-in series with a 75-watt electric lamp, and nothing so far has happened as regards dimming. The solution is fairly cloudy, and little bubbles arose from the aluminium electrode. A.: It is highly important that electrolitic fluid in these chargers be pure, The water must be pure, and the material dissolved in the water must likewise be pure. Any impurities would bring about the symptoms you complain of because they

allow a considerable discharge or reversal of current while the power line reverses. Ammonium phosphate is prepared _ by dissolving as’ much primary ammonium phosphate as the water will take up by making a* saturated solution. The crystals should then be added until there is an excess of the chemicals that cannot be dissolved in the water. The clear solution is then poured off, and is ready for use. The aluminium rod should be composed of chemically pure metal. Commercial aluminium may work and again it may not. 8. Can you describe a method of removing the glass from the base of a valve without breaking it or damaging the base? " A.: The usual thing is what you have done, to soak the base in methylated spirits. Usually, however, by working the glass backwards and forwards, it can be pulled out. It is necessary. however, to heat the tips of the valve pins and shake the solder free. ‘This will allow the wires to pull straight out. The cement can be seraped away. If you want to put the glass back again do not remove the cement, but liberally coat it and the bottom of the glass with seccotine, which is as good as anything for holding the valve together when the base is laid with cement. ’ GHUNTER (Mereer.) I propose building the Radiogram Jive, but understand that the connections for the American type valve are different from those shown. What alterations must I make? P ‘ A.: The grid connection from the coil goes to the top of the valve, and then on to the fixed plates of the radio condenser. The wire normally going to the top of the valve is carried to P in the valve socket. The connections shown to P of the valve socket are taken to G of the valve socket. 2. What is the value of the condenser shown across the three terminal gril condenser? A.: .00025 or .0003. 8. What is the minimum and maximum wavelengths that the set will tune to? .: A normal broadcast band from 250 metres to 550 metres. D W.V. (Invercargill) -A rattle has * developed in my speaker unit which I eannot eliminate. A.: You must take this to a dealer, preferably the one from whom you bought it. It will be a rather dangerous plan to try pulling the unity down yourself, . QTATIC (Christchurech).-I_ have constructed the wavetrap described in this week’s "R.R." Can I use plain copper wire if I enamel it myself? A.: Yes, but a safer plan would be to space slightly the copper windings, and allow a few less turns so that it will occupy approximately the same snace as that occupied by. the original coil. The smaller the space between the turns ithe better.

R TR, (Matangi).-I am experiencing x trouble through interference entering my set through the a.c, mains. A.: Are you quite certain the trouble is in the a.c. mains, and not in your set? If the trouble is definitely in the a.c, mains you can reduce it by connecting two or four 2mfd. condensers in series across the mains, and from the centre point take a lead to earth. This appears as shown in the diagram. If this does not have the desired effect, insert two choke coils as shown. ‘These should be 150 turns of 18 rauge d.¢.c. wire wound on a 3in. former,

H S. (Waianiwa).-Can you give me * the specifications for the charging side only of the combined power pack and (lischarger described in last week’s "R.R.?’ I shall be using a 1x1 core, on which there are already wound 1350 turns, A.: Your core should have a primary of 1875 turns, and by using a 1350 you are getting a lower number of turns per volt ratio, and probably a less economical transformer, However, if you can fairly safely reckon on 12 turns to a volt, but before actually using the outfit, it will he wise to check up your voltages either with a volt meter or with a flash lamp to the same voltage as is given for the charger in the "R.R." Ni¢8t HAWK (Temuka).-I have had good results with the Night Hawk, but there is a dead spot below 3YA. Can this be overcome by constructing a special coil? A.: In all probability, yes. Build a coil intermediate between the S0-metre coil and the broadcast band, and try that. 2. What is the capacity on each side of a differential condenser having four moving plates and three fixed? A.: Probably a .0002. .8. Do you consider a pentode in the last stage would be an improvement? A.! It is doubtful, as your experience has shown that if not matched, the pentode does not give good results. When matched up it gives brilliant reproduction. MARSITE (Te Aroha): TI find it is hard to get the condenser for the first coil of my three stage s.g. set to cover the broadeast band. I believe that 2 trimmer would adjust thisy but how could it be done in some other way? A.: It could be done only by adjusting your coil; probably by adding more turns. 2. Could you give me the specifications for a set of five coils to cover from to 100 metres tuned by a .0001 condenser? A.: Use the specifications published for the differential series omitting the tickler coil. . Can you give me the formula for working out short-wave coils? A.: A chart based on standard formula was published in the "Radio Guide." Can you give me particulars of the best way to connect a gramophone pickup to the detector from point of view of volume and tone so that it will not. alter the tuning of the set? A.: This has been very fully discussed in the "Radio Guide," to which we would refer you. WREQUENCY COP (Auckland) : What do you think of the enclosed circuit for a portable set? A.: It is not the usual, such a& that published for the "Home and Country," the diagram of which is published on page 30 of this issue. 2. T intend using either 199 valves or the new 230 type. Which will be the better? . ‘

A.: If you do not subject the set to much bumping about the new 230 valve will be the best. . 8. How long will the A and B bat-. 7 teries last using the set on an average of two hours a day? . A.: If you use the small portable tyne B batteries they will last probably three months, whereas the A cells will last about four. JQ 2TECTOR (Auckland).-I have a four-valvé set, using B406 first audio and 171 power valve. I get very loud, but blurred music from the local station, though I can move the dials just slightly off resonance, and get clearer music with less volume. Where is the overloading taking place? A.: It just depends upon how much volume you try to get out of your set. You may be overloading your speaker, for very few sets will take the full output of the local station, unless tuned down. You should not be using B406 as first audio. It is a power to be used in the last stage only. 2. I would like to change my detector into a power detector; how ean I carry this out, and would it be as sensitive as a grid leak detector? a} A.: A diagram appears herewith showing the connections for a power detector. It will be almost as sensitive as a grid leak and will handle more volume. 8. What is the gauge of the enclosed piece of wire? A.: Hither the wire was dropped out of the letter at your end or at ours, but it was not attached to your query when

we came to deal with it. Send us another sample and we will tell you what it is. R B. (Island Bay) : I have an elec- * tric eight-valve set and have logged 50 stations with an aerial only 3ft. above ns

NORRESPONDENTS must attach / this coupon to all queries sent to the Technica) Editor (Rox 1032. Wellington. Limit three questions, unless letter is accompanied by 1/ee, Name of set .. ........- ecccccees Number Of ValveS ..sceeessseeeeeees Name Srrrrrrrrrrrrr rrr rit rrr tree AGATESS coccccccccccccccccccrvces: . Soe eeerrecceresereconeossseoreveses ny Nom de plume .esececsevececcces To be kept in subsequent inquiries Date © cccvesccecescecceccccees Please Note:(1) Be specific and brief, tabu lating, if possible. . (2) Write -legibly, and on one side of the paper. (3) 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 involved specifications cannot be supplied without a specialist’s fee. »

the roof. Should I be able to pick up the Americans? : roa A.: Your aerial is not very efficient, and it is doubtful that you ‘will be able to pick up these stations. See the D.X. column for a statement concerning your other requests. piko (Hauraki Plains): I am contemplating making an Outspan Five. Would I get approximately as good results as if I used new coils and new valves in my five-valve B.D. and otherwise adapted it for a.c. operation? In other words, I wish to use the screening box now in use. A.: Yes, you would get good results. » 2, The best valves to use in. either Philips or Mullard makes? ' A.: Mullard, two PM16, PM6D, PM5X, PM256 in push-pull; Philips, two A442, A615, A609, B605. 8. Which would be the more suitable in push-pull, 603 or 605? A.: 605 would give you a greater stepup, although 603 would deliver a greater undistorted output. However, it is unlikely that you would want to get 2 greater output, than 605 would deliver, 4, Could a 66R be used with my silk speaker? A.: Yes, but you will probably have to make some adaptations in the arrangements to use it. You will probably have to have the rod tapped and extended. ATPO (P.N.): I find that by varying the grid bias on 442 I can get better results on certain wavelengths. I damaging the valves by so doing? A.: No, you are only making your set more prone to oscillate on the lower frequencies and hence more sensitive. WATILLIDO (Tikurangi); My B.D. four-valve set distorts badly. Can you give me a remedy? I am using PM4 in the first audio stage and UX240 in the first radio stage. A.: Your first valve should really be a g.p. valve of the PM3 type, and the first audio should certainly be of the latter type and not a semi-power valve ’ X of the PM4 type. 2. What grid bias is necessary on 3 \ 256 valve with 90 volts:on the plate? A.: From 9 to 12. T'xRO (Auckland) : The Australian stations come in only faintly on my six-valve a.c. set. Should the set not give a better performance? A.: It appears that the condensers are out of balance. You could have a technician true them up? 2. Is the valve combination satisfactory ?7-Yes. 3. I am anxious to learn something about radio. Can you recommend a good book other than the 1981 "Guide," which I have . A.: "Wireless, the Magic Carpet," by Ralph Stranger, is a good book, though it deals more with theory than constru+tion. It is delightfully written, and you should find it intensely interesting. R. (Woodville): I would like to get { °* in touch with the constructor who peites of his "Outspan" in the eurrent issue of the "Radio Record." He sigaed himself "G.T. (Dunedin)." Should "GT. (Dunedin)" see this would he communieate with us and we will forward his address on to J.R. (Woodville). pu. (Wellington): I wish to ereet an aerial between two houses 12ft. apart, both having iron roofs. What height would be necessary to avoid interference from the roofs? .: Get them up as high as possible, 20ft. would riot be too much, 2. Would it be better to erect the serial on the other side of the house in order to avoid passing over-the roof and near electric lines? A.: If you cannot get the requisite height it would be advisable to do this. "EN7 J.H. (Foxton): How. can I connect phone terminals to my a.c. set? A.: As the set uses an output filter, you ean use the speaker posts,

2. Could you give me an idea of the approximate voltages on the different valves? A.: We cannot tell you this, but it would probably be about that in the slip you sent us for your model. Do’ NRAD (Christchurch) : I have built the Loftin Four, but am using two 2A45’s in parallel. The set has developed

excess hum. I find by earthing the filament heads of the 224 that.the hum is deadened but causes this. A.: It is due to your by-passing, the hum frequencies originating in the 224 filament circuits. You could try an extra choke in the h.f. plate supply. 2. When the pickup is connected the hum .is very bad. 2 A.: This should, of course, not be. It indicates a wrong layout or a.wrong con nection in some respect. Try changing the position of the pickup. If you have it now in the grid return, take it over to the cathode and vice versa. 8. Is it necessary to shield the 224’s and condensers? A.: It may be. If you are troubled with instability then by all means do 80. This would not cut the hum down. 4, Was the value of the special tapped resistance absolutely correct? : No, but notice that the resistance in the main chain was 2500 not 12,500 as first stated. A diagram is reproduced herewith showing the resistances and their value, ; 5. If the pickup leads touch the lead from the maing a loud blasting and hum is caused. A.: This is quite in order. You are picking up a.c. hum from the mains and transferring to your input. . Can you supply a blue print of this set? It has a wonderful tone and power. A.: We are sorry we do not have a blue print for this particular circuit. A ®GON (Auckland): Can I connect two 1.1 volt valves in series to a supply of 2.5 volts? . A.: Yes, though whether your set operate under these conditions is another thing. They will certainly get all the power you want, but you will probably pick up hum. You will not need the 400 ohms potentiometer indicated across the filament of the first valve. The earthing will take place throwgh the .5 mfd. condenser shunted across the 3000 ohms variable resistance. Your method of obtaining grid bias is correct. BN ADHEM (Christchurch).-With .my Loftin White the 400 ohms potentiometer made no difference, " and

then suddenly the hum became greatly reduced and the set ceased to function. The filaments were all right, but I do not know about the "B" voltage, eause I have not a meter. -A.: In all probability a resistance in the bias chain has gone. If you have not a.meter you must be very careful, for if the bias chain hes gone the anode eur-

rent from the power valve would be very high, and you are likely to ruin it. 2. The set was oscillating when 3YA was tuned in, but as I had the maximum number of turns-on the primary coil, I believe this is quite in order. The ‘Tayout was as nearly as possible that given in the "Record," the only departure being a switch in the plate lead of the 250.

A.: The ‘oscillation was due probably to there being too many turns on the primary -coil, and as you’ have probably had a defective resistance from the'start, these two factors have combined to make your set troublesome, conjunction pe ? A.: Yes, it is identical with the Silver Ghost, which was advertised recently by LL. M. Silver. ; 2. I wish to build the " Hawk" one, Would it be practi to use a mid~ get condenser for tuning? _ oh Yes, if it is to be used on shortwave only. . . 8. IT have a Mullard PM2, and in all tables I can find it listed marked 150 volts max. In the literature accompanying the valve it is stated that its rating is 100 volts. Which is correct? A.: Both, the tables refer to the later types of valves, and yours is probably one of the earlier makes. Do not exceed the voltage specified on the leaflet which accompanies your valve. PARKES (Gisborne)-My set is rather broad in tuning. Is it possible to use the knife edge rejector So as. to sharpen tuning? . A.: It is possible but not The knife edge rejector will sharpen up one station only on one adjustment. This means you have to be continually: adjusting it. Tf you use an ordinary wavetrap and adjust this as you would an extra dial on your set, you would achieve the desired end, but if you used a. condenser of .0008 mfd. in series with the aerial you would possibly sharpen the tuning satisfactorily. H M.T,: Why does my set squeal when * IT use PM5X in the first stage instead of 201A? Tae A.: Your set is neutralised for « 2014, and if you use 5X you must reneutralise It. . , 2. The set has a tapped primary coil. Most of the stations come in on one clip, but 2FC and 4YA cannot be tuned in properly, because the set will not’ go out of oscillation. The primary coil con {Concluded on page 30.)

Questions and Answers

(Continued from page 18.)

sists of 40 turns‘of d.ce. Can I add a few more turns? A.: It is unusual for set to keep on O8cillating on low frequency stations. reducing the detector voltages on these. You may add a few more turns on the primary if you wish, but try reducing 3. The valves are all 6§-volt ones, conto a single rheostat, which I can turn only half on. If I go any further the set oscillates. A.: It seems as though your set is very much out of neutralisation, DXNAMIO (Lower Hutt) : Can I use my short-wave set in conjunction with an all-electric set by connecting the output with the gramophone _ terminals? A.: Yes, but you will haye to make some provision to prevent the low-fre-

eney ecurrent' getting mixed up with the a.c. set. To do this either use the adapter as described in the "Guide" or use an output filter as is shown. in the accompanying diagram to isolate the two sets. O™ (Wanganui): I am intending to alter my set to take a.c. valves and I intend to use 226 for the r.f., 227 for the detector and 608 for the second audio. What value of grid bias resisters are needed for the r.f. and detector valves? A.: The 226 valve should not be used as it is out of date. Use 227’s throughout. ‘This valve, with 190 volts on the plate, requires about 2000 ohms bias resistance. 603 requires the same. P S. (Carterton): When the free end: *of an indoor antenna is connected to the earth terminal on my set the volume is sensibly increased. Why? . A.: Because by using your aerial as a loop you are bringing the set nearer oscillation. 2. Seeing my aerial has a natural wavefength, which is increased by a coil, how is it when I use a shorter aerial 2YA eomes in on the same place on the dial, Le., seeing that L is less how is it that C does not have to be increased to give the same Le. value? A.: The inductance of the aerial is almost negligible and practically does not affect the inductance of the coil, Furthermore, it is coupled to a special coupling device which prevents variations in the length of the. aerial having any effect upon the tuning. 8. Without any adaptation of the set could I use s.g. valves?-No. 37 (Christchurch): In what issue can I find diagrams and details of a shortwave four-valve set? A.: The Differential Four in the "R.R."

of April 2, 1931, and the "Sellens’s Shortwave Set" of April 17. The latter is shortwave only, but broadcast coils the dimensions of which have been given this week to "Enquirer, Westport." 2. Would the above set give better re sults than the usual three-valve shortwave set without a s.g. stage?-Yes. 3. What fixed condenser is needed to shunt a 44-1 transformer to make it function as if it were a 2-1 or I-1 ratio? A.: You eannot use a fixed condenser in this manner without by-passing high frequency and ruining the response. C A.H, (Napier) : I.recently constrict- * ed the s.g. short-wave receiver in the: 1930 od, " and although I have varied the winding on the coils I cannot get the set to oscillate below 28 metres, _ : Try the effect of a midget condenser in series with the aerial. instead of using the primary coil. Bring this straight on to the top of the secondary coil, 2. What are the windings to cover the broadcast band?

A.: They fave been published previguely. 1 See "Radio Record" dated April M ©.B.: (Christchurch): It is my in- * tention to construct the Loftin Four using two 245 valves in parallel. Can you give me the following particulars: 1. What is the value of the resistance between the filaments of the 245 power valves?-20 ohms, as is the value of the resistance across the filament of the 224. Is the circuit diagram enclosed correct irrespective of the individual values of the various components?-Yes, Are the resistances contained in the table overleaf correct : You will find them all set out underneath the diagram on page 15. 4, Will the transformer described in the 1931 "Guide" for 100 watts be satisfactory ?-Yes. . In December 5 issue of the "Radio Record" you say that the two half-width secondaries are necessary for two valves in parallel for full wave rectification, whereas in the diagram~ you show half-way rectification. A.: Hither can be used with equal satisfaction ; 280 may be slightly quieter in operation. F. J. (Gisborne): You are referred to the previous correspondent’s query and the diagram. Note that there is a condenser between the potentiometer arm an . 1. Will a 40-watt resistance carry the current of R3, 4 and 5?. : No, you will need a 75-watt resistance. 2. How would a dynamic speaker with & field of 8000 ohms. be connected in this circuit? A.: It can n used only as a choke in the main B-- lead. 8. Does the for the 245’s connect at the two points indicated?--~Yes,

4, Is the centre tap filament necessary for the 280 in this circuit? Exactly how do you mean, and which filament do you refer to? , RE? BIRD (Wellington): My aerial is 30 feet high and 60 feet long, and I have an elaborate earth system. Is this installation good enough to get the American stations? Although your aerial eould be higher, it is good, and the fact that you do not get the American stations and have a good set indicates that your locality is at fault. 2, Should my aerial be longer? For city reception, no; you have almost an ideal aerial except that it might be 10 or 15 feet higher. BATIERY (Wellington). My 60 volt 80 amp battery has had a severe knock and one cell is dead, but the other two show a full charge. Can I use these two as 4 voltage without cutting out the dead cell? A.: If the set works successfully like that, yes. You are doing no further

harm, 2. I have a six volt 1.8. amp charger. What resistance will I have to use to charge at 4 volts and how will I connect ‘A.: You will need approximately 2 ohms resistance and this you can make yourself by obtaining sufficient 18 rauge resistance wire and winding it into a coil. You will connect it between the positive of your battery charger and the positive’ of the battery to be charged. An alternative suggestion would be not to coil the wire but to use it as a connection between your battery and the charger. REGULAR RBADER (Christchurch). I have built the five valve Radiogram described in the "R.R." but am not using push-pull. Signals are distorted when grid bias _is applied to the first audio valve. Without biasing this valve signals are much stronger and clearer. .: This is not altogether unusual because some sets do not use bias on the fst audio stage. It will be quite in order to leave out the resistance. I notice a spark when I connect the eentre tap of my filament transformer to rth. A.: If the set functions quietly without this connection, do not make it, for the spark originates probably because of all the filament power coming from the same source. H L.M. (Milton). What type: short*wave adapter should I buy for my four valve set? : Write "Mack’s Radio, Wellington," or any other reputable dealer. THANKFUL (Timaru).-I have built the "Outspan Five" but cannot get the set to work with the coils eorered, I can get no signals at all,

A.: It seems that by’covering the coils you are earthing a part of one. Probably the can is touching a loose end. 2. My aerial is 45 feet high at one end, %0 feet at the other. Is this satisfactory? A.: Yes; your aerial is actually about 55 feet high, 8. Is my earth too long? . From the distributor point just outside the set four wires go to different earths. The longest is 12 feet. A,: No; the earth is quite satisfactory. WwW H.B. (Christchurch).-Tone is in- * variably harsh and heavy when plugged into the second audio, although the output from the first stage is good. I am‘using a B409 in the first audio stage and a B409 in the second. A.: This is wrong. A power valve ) should not be used in the first audio stage. Use A409, and be quite certain that ye B409 is biassed properly. 2. Would an output "transformer or’ tap choke be best for my set? A.: Hither a tap:choke or an output transformer would be satisfactory. You need a 1-1 transformer. 38. Am I using the correct valves? A.: With the exception of the first audio, yes. KENTY (Manuniu)-What current would a torch bulb draw?. ane? Most torch bulbs draw about 3ne. What type and value of resistance is used for a 2.5 bulb used in connection with a 6-volt battery? AA resistance of about 10 ohms. 3. What wires connect with B+ and P on an output filter? A.: It does not matter which, as direct eurrent is not flowing and cannot harm your speaker. K 0.8.0. (Wellington).-Would it be * possible to fit the "Sparrow Hawk" / Differential adapter to my _ three-valve s.g. set? A.: Yes; you could make an adapter to fit in to the detector socket. You would not get a great number of stations from the gpeaker, though you would get good phone results. 2. Which is the detector valve on a Cossor three-valve Melody Maker? A.: The second one, L D.H. (Te Aroha)-From what firm can I obtain the bakelite bobbins and No. 4 stalloy stampings and a clamp for the transformer used in the power unit described in the "Radio Guide"? A.: From any firm which sells companents. The No. 4 size is one inch wide. 2. Would a 30-henry 45 m.a, choke be suitable for the above power unit?-Yes. PTIMISTIO (Dunedin). Can I u three .00025 condensers for the span Five? If so how many turns would be required on the coils? : Yes, if you are using 26 gauge enwire the secondaries should be 105 turns, and the primary from 25 to 30, and the tickler 45 2. What secondaries must I put on 100 watt transformer to make a Tunga charger? A.: The bulb requires a very high filament current. It will need to be wound with 14 gauge d.cc. wire. If you are intending to charge a six volt: battery you . must wind on 45 turns and take a tapping at 20 turns for the filament, The resistance must be used in one of the leads to regulate charging rate. EN FAD, (Gisborne)... When I switch on my three valve set I am troubled by, a loud motor-boating and I cannot receive any station other than the local. A.: Have you tried changing over the primary connections to your audio transformer? Failing that, use the antimotorboating device illustrated herewith. Are you quite certain your "C" battery is eonnected round the right way with the negative connected to the secondary of the aranstormer and that it is of the yaiue