Questions and Answers

Radio Record, Volume IV, Issue 9, 12 September 1930, Page 24

Questions and Answers

D S. (Market Cross).-Do you con- ’ sider the enclosed specifications for an eliminator to work from 32 volts d.c. satisfactory? A.: Yes. As far as we know these units are made up of Edison cells to any voltage, provision being made to parallel the blocks for charging when the voltage required is greater than the mains. They are really wet batteries, and are practically indestructible. 2. Would it supply sufficient for two minus 171 A’s in the last stage? A.: In all probability yes, but it is hard to determine from the amount of data given. 8. What valves with low filament consumption would replace two minus 112 A’s, as detector and first audic in an American model receiver.-UX&£. .. JoMARF (Oamaru).-Could you give the the constructional details of frame aerial. A.: They were published in the "R.R." on December 6, 1929. 2. Could I use a short-wave adaptor with.a 7-valve a.c. set?-Yes. Where could I find particulars of such an adaptor? A.: In the 1980 ‘"R.R.- Listeners’ Guide." 3. Would you advise building an adaptor or a short-wave set? _._ A.: A short-wave D.C. set would be the more certain for results. J B. (Nelson).-Can I add oa stage of * rf to my 4-valve parallel feed B.D. If so how? A.: Yes; the 2 r.f. parallel feed B.D. was described fully in the 1929 "Listeners’ Guide." | a a ne a a a a a a a aaa a a a a a a a a ae ee ae ee ee ae ae ae

2. What voltage should I apply to the detector first and second audio and r.f. tappings on my set? A.: RF equals 90; Det equals 45; 1st audio equals 185; power equals 150. 8. What bias would I need to apply to these valves? A.: We eannot state unless we know the valves you are using. 4. Would I need to shield any of the stages and would sheet brass do?

A.: The three stages, rf. and det. should be shielded with sheet iron or aluminium, but brass would do. 5. Would I need to alter the coils? A.: The specifications are given in the 1929 "Guide." To use two r.f. stages the aerial coil and regenaformer remain as they are, and the first r.f. coil is similar to the regenaformer without the tickler, providing the same condensers are used. 6. Are the number of turns on the r.f.c. critical ?-No. BUNG (Hamilton) : a 10-valve s.g. super-het. as ne as a 10- valve S.g. receiver using an aerial? A.: No; the former is designed for use with a frame antenna for areas where it is inconvenient to use the outside aerial. uld I add an extra stage of sg. using one s.g. and three ordinary valve,

or could I put a pentode in the | last stage? . A.: You could add a stage of screen grid if you followed out the circuit published in last week’s "Radio Record." The pentode could quite easily be placed in the last socket with the auxiliary terminal connected to the highest B-+-. 3. What is a vario-coupler? . A.: A vario-coupler is defined in the "Listeners’ Guide’ as "a loose coupler of variometer design having a coil rotaing inside another.". It is a method of tuning a radio receiver by varying the inductance rather than the inductance and capacity as is the case with the ordinary receiver. 4, What is the cause of the set making a singer or speaker sound as though talking through his or her nose? A.: If it is only occasional, and your batteries are up to standard, it is distortion due to your locality. C.B. (Nelson): I have built the "RW. Two," but it is not going very well. I. have altered the value of almost everything, and the set will not oscillate. A.: The failure to get results is caused by the alterations you have made. Yor instance, you have altered the value of the tuning condenser from .0002 to .0001, and this will quite alter the tuning range of your coils. They were designed to oscillate with the .00035, but you are using .0008, consequently you must add more turns. Your coils will have to be redesigned for a .0001 condenser. If you state the size of former you intend to use throughout, the gauge of wire available, we will design them for you. We strongly advise constructors to adhere to specifications. Failure to obtain results is more often caused by this than by anything else. Altering specifications to suit the correspondent’ requirements is a long job, and we do not particularly welcome It. e M K. ( ): I have a Western Volt ! * ammeter reading 0 to .1 volts, 0 ~ to 8 volts, and 0. to 30 volts. I wish to

increase its range to 300 volts. What resistance must I use in series? A.: We need to know the number of ohms per volt. This is usually marked on the meter. However, if you use a universal resistance and calibrated the ‘meter with a known source of supply, you could arrive at the setting by experiment, GHORTWAVE (Auckland).-Could you supply me with valvebase coil data for the Cossor Melody maker? A.: Your best plan is to use a .002 m.f.d. fixed condenser in series with the existing variable condenser to reduce their capacities to 00015, and then construct the coils described in the 1930 "Radio Listeners’ Guide," page 95. We are returning your 6d., as the only coil data for the Cossor that we have published was the specifications on the standard coil former for one band. A G.B. (Wellington).-I enclose a dia- ¢ gram of a erystal and valve with three-valye performance designed to operate from the mains. Is this circuit satisfactory? A.: Yes, but it will be advisable to use a variable resistance for grid bias. You ean use either PM3 or 201A. We do not know the other. D.H.I.

BAx (Christchurch).-I am using @ new professionally-made three-valve kit set, and can pick up only two stations on phones. Why should I not received other stations? ; ‘ A.: Your best plan would be to ‘take the receiver back to the dealer who de ° it and state your case. You should" get better results. 2. Which is the better valve combina-tion-L410 detector and two P.410’s, or two 415’s and one 410? A.: The second is by far the better; in fact, the first is quite wrong. P.410 is a last-stage valve. : ANe@uUs (Wanganui).-What are the specifications for coils using threeganged .00025 tuning condensers? A.: You have not stated the type of wire you wish to use, but we recommend 72 turns 24 d.s.c. wire on a 24in former. 2. If the sereen voltage is higher than the . detector voltage fringe howl is bad, otherwise the set is quite satisfactory. . A.: This is a characteristic of the circuit or the valves. So long as you get good results, everything is in order, 8. My aerial is only 20 feet high, and the lead-in runs for twenty feet over the roof, The Australian stations come in at their maximum strength at five o’clock... A.: It would probably be better if you increased the height of the aerial, 80, that it cleared the roof, leaving more margin. pisko (Hauraki Plains)-I am _ not clear about using a 200,000 ohms resistance in series with the plate leads to the eliminator, as I already have an rf. choke in the same position. Must have another condenser placed in parallel with the resistance? A.: Providing the plate voltage can be controlled satisfactory from the eliminator there is no need for the resistance and by-pass condenser. In any case, using parallel feed there will be little need for a condenser across the resistance. BARNER (Lower Hutt).-I have a three-valve all-wave set. Could I add another stage of audio?

MANY correspondents still ask questions and do not append the coupon. They cannot expect to be given priority over those who do.

A.: As you are already using two . transformers, no. NGHL (Palmerston North).-About t what would be the cost of the materused .in the short-wave adaptor deseribed in the "R.R. Guide." A.: Approximately £3/10/-. LONG-WAVE (Auckland).-On a twovalve set how far should I.be able to receive? I am using 45 volts. A.: Little more than the local station satisfactorily. You will need higher voltage before you can reach other stations, 2. Could my set. be converted into a short-wave, and about what would be the cost? A.: You could use the parts in assembling "Round the World Two." You would need to reduce the capacity of the condensers with a series condenser. The eosff would probably be less than £1. %. Is the Octron a good valve? ™ We do not know.it, but presume it is one of the 201A type manufactured under license from the R.C.A. You should know if it is as good as the standard by the price. It should not be under 4, Is the a good transformer? A.: No, it is a cheap one. G M. (Dunedin).-Where could I ob- * tain a diagram of a two-valve short-wave receiver using 199 valves? A.: Construct "Round the World Two" — in the "R.R." February 28, 2. How far should I be able to reach out on earphones? A.: This set will bring in London, and _ Russia, ONTROL (Invercargill)---When I touch our dynamic speaker with any metal object, it can be heard in the speaker. Is this right?-Yes. 2. What is the consumption of our set in watts? : A,: 60 to 80. 3. Is our aerial of excessive length, 45 feet high, 115 feet long? A.: Yes; unless you are troubled with excessive noise, or lack of selectivity. do not alter it, otherwise try .00025 condenser in series. 4, The dial light flickers. Is this a fault in the set? A.: It may be loose in its socket, otherwise you should consult. the agents who sold you the set. T.A.. (Ngunguru).-Can the first * charge for the B accumulator described in the 1930 "Guide" be given with a car generator? A.: If the directions in the "Guide" concerning the rate of charging are followed, the operation could be carried out successfully with the generator. Of course the B battery would have to be divided up in series parallel so that the

section receiving the charge would be slightly less in voltage than that delivered by the generator. 2. Would a Daniells cell charger besufficient to keep it charged? : Yes, if the B battery is broken up in sections slightly less in voltage than that supplied by the chargers. N D.B. (Tolaga Bay).-If I cannot ob- * tain 1.5/8-inch tubes, how many turns: would I require on 14in, tubes for Akarana band pass four? A.: The number of turns can quite conveniently be the same as the small difference in diameter will make only a ~ negligible difference in tuning. 2. Could short-wave be received on this set if fixed condensers were arranged so that they could be switched. in series with the tuning condensers? A.: Yes; to find out the number of turns for the coils, you would have to do an amount of experimenting. You could use as a basis the specifications given for valve base coils in the 1930 "Guide." 8. Would the set be more sensitive than the B.D. with an s.g. valve? A.: No; but it would be more selective. 4. Could the Akarana B.P. 4 be built with two stages of s.g., and regenerative detector ?-Yes.

CURIOUS | (Auckland).-Is the cabinet model of receiver superior to the table model, and why? A.: The cabinet provides a_ bigger baffle, and this improves the tone. 2. Which is the difference between two models (cited) ? .: 66 is an a.c. model, with three stages of screen ‘grid, one of 227 and two of 250. The other is a battery model with three stages of 222, one of 112A, and two 171A’s. Note.-Sorry, "Curious," be we cannot compare commercially-made receivers. [ATERESTED (Auckland).-Why do we get much bétter reception from the B class Dunedin station than from the A station? A.: This appears to be locality trouble. Our own experience has been that 4YA is the most reliable. ADIO FIEND (Halcombe).-When " the aerial condenser is tuned below 80 degrees, everything is cut clean out, but bad motor-boating commences. Be low the centre point of the dial the read-

Ings do not agree. A.: It seems that the moving and the fixed vanes are making contact below 30 degrees, and in the other that the coils are not properly matched. There may be stray capacity due to proximity of metal parts or the condensers may not be of the same precise value. .2. I tried altering the aerial condenser by seriesing several fixed condensers. They altered the reading backward and forward. Why? A.: You were altering the capacity of the tuning condenser, and this would naturally affect the reading. A W.W. (Otago).-How ean I elimin- * ate hum pick-up from electric light mains when I use long leads from a crystal set to headphones in- another room. A.: The leads may be too close to one another, or run too close to the electric light mains, ; : CQONTROLS (Gisborne).-What are the number of turns and size of wire to tune between 15 and 110 metres, using 00015 tuning condensers, and a 2kin. former?

A.: 16-30 metres 3sec, 4 tick. 28-45 metres 6see. 5 tick. 48-65 metres 1lsec. 6 tick. 62-115 metres 20see. 7 tick. These may have to be varied slightly. 2. What resistance is used for 200A and 201A valves? A.: 4 ohms for the detector, and two for the a.f. 8. I have the adaptor in the 19380 "Guide," but get motor-boating. What is the cause and the cure? A.: It is due probably to the grid circuit of the adaptor coupling with either the plate leads or part of the set. The leads should be short and well away from one another, and if necessary should be shielded as described. Are you using the small battery?

ROTON (Gisborne)-Can I use 4 screen grid valve in the detectot stage of my ‘kit set? A.: Yes, a circuit will be published in a month or so. Fs Could I add an extra stage to this se A.: Yes; the method was described in the "RR" about a month back. 8. Which would be better, a further stage of detection or another stage. A.: The ordinary receiver has only one stage of detection’ Two are found in heterodyne receivers, so you had bet« ter add another audio Do you know of a two-valve ampli fier that would go with this set? A.: You can add only one valve ows ing to- coupling taking place when ther€ are more than two transformers.

S our waiting list is now, with a few of last week’s. queries, brought up to date, would any correspondent who has_ written in and not received an answer, communicate again, restating his problem,

5. My: loudspeaker vibrates. A.: You are probably giving | it too much volume. Try" adjusting the diaphragm or use a filter. C ©._ (Hikuranga) -What valves shall * I use in the short-wave set described in the 1930 "Guide"? I am using 222 screen grid, and a 4-volt accumulator. A.: Mullard, detector 4DX, first audio, P.M.3, second P.M.4, detector 415, first audio 409, second audio 406 for quality, or 409 for volume. Osram, 10, in sll stages, or P410-if quality is desired, L. S.B. we eetahana) --What valve would you suggest for my --- receiver? A.: A two 221A’s, detector 200A, last gtage 112A 2. My set fades on Auckland. Will ga new valve improve that? A.: Probably not. It is an atmospheric phenomenon. 8. When tuning the filament current eontrol to halfway volume ig at a maximum. Why A.: Because at this point the valves are heated to their optimum temperature, and further increasing the ‘current is likely to damage the valve. 4. Is the enclosed diagram eorrect? A.: If you are using 112A you should use 9 volts, grid bias. A. T.C. (Wellington).-Can you supply me with a three-valve circuit? A.: You can either add another valve to your existing receiver, as shown in

our. issue of August 8, or construct "Round the World Three," described on March 7. PT MPEDENCE (Christchurch) _-When the gramophone pick-up is plugged into the set I cannot get enough volume. Would an impedence transformer improve this? A.: An ordinary inter-valve transformer would be better. 2. Can tone be improved? A.: From the table of your valves it appears that the last two 45’s are not balanced. Consult your dealer. T M.L. (Kilbirnie).-I intend building * Pentode’s crystal and valve with three-valve performance, Has the set been redescribed? . . A.: No; the original circuit is perfectly satisfactory. 2. Could another stage of audio be added? A.: Yes; as was described about a month ago. .

.. ef OM eg ISTENERS must attach this coupon to all queries sent to the Technical Editor (Box 1032, Wellington). Questions arriving without it are likely to go astray or be delayed. Name of set cccccocsccocccccacccces Number of Valves cccosccoccccqc0ce Name soncsescesbeseucenssseenscs Address 00000000000000000000000000 eee ooTOBOOODOSFOOUDODOGHOCAGOODO9G9ODI00® POOCEHOOAOOOTOVOGOOOSOOOSGSOOIOSTIIAOHOOOOS Nom de plume © +00000000000000000000 To be kept in subsequent inquiries. Date peveccccccecvcccecccccescccoee Please Note:(1) Be specific and brief, tabulating, if possible. (2) Write legibly, and on one side of the paper. (3) We ao 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 ‘ gpecifications cannot be supplied without a specialist’s fee. ;