Questions and Answers

Radio Record, Volume VI, Issue 10, 16 September 1932, Page 13

Questions and Answers

EW CHUM (Wellington): I cannot lat get the "Differential One" to oscilA.: Try reversing the connections to the tickler coil, doubling the number of tickler turns, trying a different r.f, choke, checking the wiring to see that the choke is in the right lead, raising the detector voltage, and as a final resort shunt a -0001 condenser between one. of the sets of fixed plates and earth. . My aerial is 90ft. long, and 35ft. high. Would a longer aerial be better? A.: This would bring in greater signal strength, but the set would be more diffieult to get to oscillate. ‘Incidentally, trying the effect of a series condenser of about .0001 in the aerial may improve oscillation, 8. The reception of 2YA and 2ZW are excellent, yet I cannot get any other stations, A.: A one-valve set will not get very far, although, if you get the oscillation working correctly, you will probably be able to bring in at least a few outside stations. Your coils appear to be about right. It may be necessary to use more reactjon turns, and a few less on _ the aerial, . (rRkcuIT (Auckland): I can get only the Auckland station on my one-valve set. I have a 2-volt s.g. valve. but am notusing the screen. A.: This is probably why you are not getting good results. You must use the screen. For a suitable hook-up, see the "DX Two," described in the first issue of the "Radio Times." You can use phones instead of the resistance capacity unit. It should be an excellent circuit for your purpose. TTONB CONTROL (Pahiatua): Your best plan is to get in touch with the agents who sold you the tone control, as it is possible that it is defective. [NCERTAIN (Christchurch): Your circuit appears to be satisfactory. The broadcast coil would comprise 24 turns of 30 gauge d.s.c, aerial, 70 turns 30 gauge secondary, reaction 20 turns 30 gauge wire, that is for a 2in. former, -00035 tuning, .0003 reaction. Particulars of shortwave coils may be obtained from ‘the tables previously published in the "Radio Record." Use a 50,000 ohms. R38, 250,000 ohms, R4 .5-1 meg. RS 450 ohms capable of carrying 40 mills. ©2 .0001, C4 4 mfds. for good bass reproduction C6 .002-.006, according to your idea of tone. Unless the circuit were built upon a solid metal chassis, and the ‘ eoil thoroughly shielded from the rest of the ‘set, motor-boating would be troublesome. 57 could be used as a detec"2 = a

int tor. We cannot supply a circuit, as if you will read our coupon you will see that we cannot undertake to do so, You should get ideas, however, from _ the modern one described in the current issue of the "Radio Times." A Telsen power output. choke should be suitable for the pentode, We think this circuit should have greater amplifying powers than the Loftin White. R S. (Auckland): I have a seven-valve * electric set and cannot pick up 1ZM, which is 14 miles away, yet I can get it on a erystal. A.: Your condensers may be out of alignment, or your set may not tune low enough. If you do not know how to set about lining up your own condensers, call in a serviceman, Q R.M. (Auckland): I cannot get the * battery superheterodyne adaptor to work with my a.c. set. A.: Dry reversing the connections to the oscillator coil; increase the B plus voltage to 90 volts. Asa final resort add more turns to the oscillator coil. B minus is connected to either A plus or A minus. QCREEN-GRID (Dunedin) : Over what band does the longwave switch of the Super Six tune? A.: Approximately 200-550 metres. 2. Both B plus leads are plugged in to B maximum on my eliminator. Recently I added another audio stage, but with the added valve there does not seem to be enough power to supply it. A.: Even with the extra audio stage your eliminator should supply enough power. Are you certain the grid return of the power valve is all right, and that it is not being shorted with a resultant large drain upon your set? Possibly there is something wrong with your eliminator, H JS. (Auckland): Without a circuit ° of the proposed alteration to your set we cannot advise, UNCERTAIN (Christehurch): Your circuit appears to be quite satisfactory. However, 2 somewhat similar one will be described in a forthcoming issue of the "Radio Times," and from it you should be able to get a great deal of information. 2. Using 250-270 volts B and adhering to the values given in the circuit in this month’s "Times,’’ would the values marked be correct? © A.: They appear to be all right, but we cannot undertake to diagnose your circuit thoroughly. 8, What is the reason for the 10,000 _ ohms resistance connected in the s.g. lead of the 57 to earth? | A.: It is a bleed resistance to maintain a fairly constant potential on the screen valve, Without this drain it would be impossible to get constant potentials, seeing that the screens take very little — eurrent, . : 14] 4: (Kingsland): When I tune the ~ : locals and handle the volume control, a slight rumbling is heard, and | the control itself is very sudden. A.: Apparently there is something | wrong with the volume control, but exactly what it is impossible however, to | say without analysing your set. Af M. (Nelson): What is the size of ¢ the tuning condenser of the Differential Adaptor to be used with Spartow Hawk One coils?-.0001. iD W.P. (Wellington): We cannot un- ¢ dertake to give you the coil data required. You will probably have to experiment to get it correct and even (Continued on page 23.) 4 >

Information Coupon (To be used with all requests for information. ) Name Of BCt rccceccencccececcccees Model Name Address POoeoDS OO eS HCOS SO SDOO BC OEOES SOSSHAPOSISOSIOLOGSOSOOOOSOGEOSD 0900088809 0089000000808009 TIT ITIT ITT IT TT ITI TriiTiTTTriTrT Tre SPOSSCOSTHSTETEHSHSSCOCHESEEGSSIOTOSSOEOED Nom de plume .sccccccsccoesccces To be. kept in subsequent inquiries, Please Note:(1) ze Specific and brief, tabue ating, if possible. (2) legibly, and on one side the paper. (3) ) We do not design circuits, (4) Limit three questions. unless 1/- is enclosed. (5) Postal queries limit three questions. Enclose stamped envelope and 1/- fee.

Questions and Answers somo (Continued from page 13.) then if it were not absolutely true you would cause interference. Tt is not our ptactice to encourage readers to experiment with oscillator coils. As a matter of fact your circuit contravenes the regulations.

N I.A. (Auckland): We are afraid we * cannot help you. Your best plan is to get in touch with someone locally who knows something about your set and the adaptor, — BLvuEY (Waiuku): By connecting the earth wire to the aerial terminal the vélume is the same as before. Is this harmful?-No, 2. How can I connect a dynatiie speaker to my a.c. set? A.: You would need to use either one that derives power from the a.c. mains or which works with a permanent ficld. In the case of the former you wouid connect the field to the mains and then in the case of both connect the voice coil to the binding posts to which the ordinary speaker was attached. PENTODE (Papakura): Sorry, the coil particulars for the "Kriesler Fiye" are not available. As far as the circuit is concerned, we ean give vou no further information, but we will try to help you if yqu get into difficulties with the kit itself. C.. (Thames): {fs enamelled, 7/22 * aerial wire much superior to tinned? A.: No. The difference is negligible. 2. Is a 40ft. single pole, tlon-dircctional aerial superior to 2 -80ft. two-pole flattop one? wie A.: No; we think the latter would be the better 4erial. UZZLED (Livingstone): 1 haye two bicycle generators each rated at + volts .8 amps. If I connect these twe in series will they deliver 8 volts. .6 amps or 8 volts .O- amps? ©: ©. «| ~A.: 8 volts .3 amps. "In parallel, + volts G amps. ~~ , 2. Would the two dynamos connected, as above be suitable to trickle charge the accumulator? A.: No, as the bicycle generators would probably be a.c. ‘ 8. Would two PM3’s in push-pull. stand more yolume than'a PM4, and what plate

milliamps would the two PM4’s in pushpull use? sy . A.: Two PM3’s would handle volume than one PM4.. Two PM4’s in push-pull, double biased; would-use from 4-5 milliamps. The radio Call Book is unobtainable, but a sécond edition is being prepared and one of these will be sent, you. os Y. (Dunedin): Will the 227 valve * work satisfactorily as first and second detector and oscillator -with the a.c. super. six ?~Yes, ; 2. Will I have to screen the 224 valve? -~Yes, * 3. Will a 3003 power unit supply enough eutrent for three 227’s, two'224’s, and one 245? "eet! A.: No, the 245 will have it beaten, we think. ri. ; 4, Will I have to put bias resistors in the first detector, s:g. valve?: If so what will they require? A.: We shall publish in the next "Radio Times": the cireyit of the a.c. 8.g. super six using 224’s and 227’s. By putting in a mains switch do I cut out the three-pin switch-Yes. Your flex is quite satisfactory for ‘wiring the filaments, but keep jt twisted., The specifications for a suitable filament transformer appeared in the 1930 "Radio Guide." . G T.M. (Auckland); Will you give the © broadcast coils for the P.OJ. Your? . Av: With .00015 for tuning use 28. d.s.c. wire, winding 100 turns on the secondary and 30 turns of 36-d.s.c. on the reaction, while for the r.f. coil you will usé the same secondary, with 25. turns for the primary, wiring as before, For the second coil you will need.195 turns on each secondary, of 82 d.s.ew wire; 50 turns for reaction on the anode coil, and 40 turns on the aerial coil. Both these are wound with 36 d.s.c. wire. The wire you specify would not be satisfactory, as it would make the coils too. bulky. 2. I have 2 — .00035, 1 — .0002, and 1 — .0005 variable condensers from an old set and wish to use some of them in making up the set instead of buying new ones. A.: The tuning should be done with a .00015 condenser, so in seriés with each | .0008 use a .0002 fixed condenser. For the reaction coudenser use .0002 condenser. 3, Is the circuit I intend to. use the best one using s.g. valves for broadcast reception ? A.: If you are wanting to design a special broadcast set, we think you would be better to follow one of the recent descriptions in the "Radio Times." However. as an all-wave set it would be very good.