QUESTIONS AND ANSWERS

Radio Record, Volume V, Issue 27, 15 January 1932, Page 11

QUESTIONS AND ANSWERS

FRANK

KEE

The Technical Editor will, through these columns, be pleased to help readers experiencing trouble with their sets. Queries are limited to three-for more. than this a shilling fee is charged, and a similar fee is payable for queries answered by post. Supplying layouts, cireuits and solutions of intricate theoretical problems is beyond the scope of this service, A coupon must accompany all requests for information, Nonappearance of the coupon in any issue eannot be regarded as a reason for its not being used. Address all queries, The Technical Editor, Box 1032, Wellington.

‘A } (Wanganui): What is the ap- ~ proximate life of an eliminator and that is the difference in cost between running an electric set and a battery set; also the cost of an eliminator? A,: A good battery eliminator may be had for sums varying between £5 and £7/10/-. Its life is almost indefinite, although the rectifying valve may want renewing after about two years, while oceasionally a resistance or a condenser breaks down, but the chance of any of these happening is very small and an eliminator can be regarded as something permanent, The eost of running an eliminator is almost negligible. It takes very little more electricity than a 20 or a 30 watt lamp. It will probably ryn 50 hours on a unit, which usually costs about 4d. The cost of a battery, say you provided two batteries to give 90 volts, would work out at approximately $d an hour. | PAT (Rangiora): Place the Ferranti transformer first. 2. What is the average life of my 108 volts battery? A.: That depends upon how much current your set is taking. It will probably last from six to eight months. C G.I’. (Woodville) : I. constructed the ° shortwave adapter described in the Radio Handbook, but on connecting it to my a.c. set it will not work, A.: Have you been trying to use a sereen-grid valve as detector where a 227 is specified? It seems you have, and have been causing complications thereby. Wirst of all see if your set will work on phones. You make the filament connection as shown in the diagram, that is the filament of the valve sockets in your set. Take the plate leads instead to one tag of a pair of phones,

take the other tag to the plate socket of the detector valve in your set. You should ‘then be able to get the. set working. If you cannot under the circumstances, it will be impossible to do so when connecting the adapter up to the set. The adapter could not work in the first audio, which is designed for a 226-valve, and there are only 1.5 volts on the filament, You are using a 227 detector requiring 2.5 volts. Your best plan would be to construct a super, het. type of adapter. One of these was described in the 1981 "Radio Guide," Of the two coils, L1 is the tuning coil, and is the langer, L2 tis the reaction coil, and is smaller. . , BEGINNER (Auckland) : Without further details we cannot say if any harm is being done to your set by the alterations mentioned. However, if a radio sefviceman has done the job, and the set now works satisfactorily, you can rest assured that everything is quite in order, EK W. (Christchurch): Short-wave sets * are génerally better when two separate coils are used for reaction. You are using the Reinartz circuit as different from the Schnell, which is generally considered to be the better. The "Night Owl Two" recently described in the "R.R." utilises a Schnell circuit. If you change your circuit round to this we think you would get better results. A V.B. (Petone): Could you tell me if * enamelled-covered wire is suitable forthe secondary winding of a 150-watt transformer ?-Yes. (RONA (Napier): Would you tell me where to fit a milliameter in my set, so as to obtain the total consumption that the set is using in mamps? A.: Break the "B-" connection to the "B" battery and insert your milliammeter there. The positive will be toward the set, and the negative to the battery. IWL (Arapuni): My power transformer is 24 volts out of balance, there being 197.5 on one side of_the centre tap and 200 on the other. Will this be detrimental to its performance? A,: A.small difference such as that will be negligible, particularly ‘as the power pack will have ample smoothing. 2. Could you supply the output curve for the 1560 valve? A.: We are afraid we cannot. Unless. you can get it direct from the New Zealand agent you will have to do without it. The valves will not deliver a higher voltage than the power pack voltage even under light load. OMSE (Bay of Plenty): What would be the cost of a four-valve a.c. set, and will it have to have a rectifying yalye? A.: We do not happen to know of a commercial four-yalve a.c, s.w. set, although Johns Ltd., Radio Ltd., or Silver

Marshall mav have one. We think, however, you could get one built up for abgut from £15 to £20; maybe less. However, a dealer could tell you better than we could. If you have already a good commercial set, why not use an adapter? A suitable short-wave super-het. converter could be obtained for about half the sum previously mentioned,

awe A C. (Manurewa): How can I find out ¢ wavelength in metres from kile cycles? . A.: Divide the number of kilocycles into 800,000. 2, My "B" eliminator takes some tima to get into stride; the signals are very weak to start with. . A.: There is something wrong

ae. the eliminator, Have it tested by a reliable dealer. It may be that the valve is at fault. INU CHUM (Havelock North),-Is it possible for an amateur to build a shortwave adapter for-an all-wave elecjtrie set? Where could the circuit and Jayout be obtained? A.: The most suitable adapter would be a super het. One of the type describ@d in the 1931 "Radio Guide." See the article on stite Ten adapters in this fmonth’s L . Can one particulars of the PRadcord Crystal Set? ?" : This set, was described in the 1950 EE Guide."

R B.C. (Raetihi)-Could you give a * brief description of the Beverage frerial? A.: A Beverage aerial consists of a ‘wire about 400 yards long, slung about ten feet above the ground just clear of stock, ete. The wire is not necessarily stranded wire and can be ordinary galvanised iron wire, The distant end must be earthed to a 750 ohms _resist@nce. 2. What are the chief advantages of a Beverage aerial? __ A.: The signals are brought in louder they are on the average aerial. It is strongly directional and the end which is earthed must point toward the stations which are to be supplied. 8. Can you supply information or feature an article for the construction of a shortwave converter? A.: See the reply to the above correspondent. A complete description of the

Berevage aerial appeared in the 1981 "Radio Guide" and in the "R.R." ONSTANT READBR (Gisborne). — My five valve screen grid set radiates. Can you tell me a good circuit that will not? ; A.: A screen-grid set, unless it is very poorly designed, will not radiate. Are you quite certain your set is radiating? Do not listen to everything you are told. The "Radiogram Five" is not a radiating set. A 473 (Helensville).-Is it safe to dis- * connect the speaker of an allelectric set while using phones? A.: You can disconnect the speaker voice coil but not the field, which is usually incorporated in the power pack. If, however, the field supply comes from a separate retifier you will be quite in order to disconnect it entirely. W B.E. (P.N.)-A fortnight ago the * speaker of my six-valve set started to heat although the tone and quality are splendid. A.: It sounds as though you have a breakdown in the voice coil which is now passing more current than it is designed to do. You had better consult a radiotrician who can soon tell you if there is anything wrong. Neglecting it may possibly cause more serious trouble. 2. What is the correct place for a pickup jack in the set? A.: Between the grid and cathode of the detector. BERDONIAN (Wellington) -Can I use a three-yalve set with batteries? I am now using an eliminator. A.: Yes, the set will operate quite satisfactorily on 120 volts "B." 2. If I decide to alter the set to a shortwave five-valve set, could this he

done without mnch outlay or drastic pulling to pieces? , A.: It is usually not a practicable proposition to pull about a commercial set in order to change over to shortwaye or ae, M C.B. (Christechureh).-The "Cath- * ode Super" which will appear in a week or so should suit your purposes admirably. The Australian "Wireless Weekly" have published many articles on super. hets. and if the "Cathode Super" is not to your liking and you wrote them, they may be able to put you on a circuit they have published.