QUESTIONS AND ANSWERS

Radio Record, Volume VII, Issue 6, 18 August 1933, Page 27

QUESTIONS AND ANSWERS

"WY Y.Z’? (Dunedin): I can receive 1YA * and the main Australian stations quite well on my 5-valve set, but I cannot hear 4ZL, Dunedin. . ‘ A.: Evidently your set needs re-align-ing. 4ZL has a low wave-length, and is evidently just outside the band now covered by your set. .F.P, (Wellington): Would a trickle charger work as efficiently with the 230-yolt mains plug connected either way? A.: Yes. S. (Waikato): My present aerial is * 220ft. long and selectivity is very poor. However, I cannot shorten it as it passes over a lawn and tennis court. Would a new aerial erected in the position shown in my sketch be an improvement? A.; Yes. Selectivity would be greatly improved as the new aerial is much shorter. However, why go to the trouble of shifting one of the masts from its present position? 'To shorten your aerial by 100 feet, use this length of additional supporting rope, thus bringing the insulators at the most distant end of your aerial about mid-way between the two masts. A M. (Wellington): I am considering "building the one-valye set described in the 19383 "Radio Guide," and I wish to use it for short-wave only. Could you give me the coil details using a .00015mfd condenser? A.: Specifications as given in the article will be quite suitable. Any additional details that you may require can be quite easily obtained from the chart given on page 120. " AMATEUR" (Christchurch): We strongly. advise you against building a superheterodyne short-wave converter. especially as you intend to use it with a broadcast superhet. "[NQUIRER" (Wellington): I have a 7 valve set employing 3 51's, 1 24,1 27, 1 47 and an SO rectifier. What replacements do you advise? A.: Replace the 51’s with 35’s, and the 24 with a 224A, 2. Can you state briefly the purpose of each valve? A.: The 235’s are used for the r.f. and if. stages; 227 as oscillator; 224A as ‘«

"second detector and the 47 ag output valve. 3. What causes fading in my set? A.: This is very likely due to a wornout valve, ID*2254 (Auckland): Could you re‘commend a simple two-valve shortwave set, and where can I obtain details? A.: The "Short-wave Club Two" described in the November, 1932, "Radio Times." 2. What type of aerial is best for shortwave reception? A.: A well-insulated aerial about 30 feet high and 60 feet long will be quite suitable, though a more efficient type of

aerial is shown in the accompanying sketch, which is self-explanatory. ‘Twisted rubber flex can be used for both the horizontal portion and the lead-in, though ordinary aerial wire can be used with the horizontal portion if desired. The primary winding on the aerial coil should, of course, not be earthed in this case. "FULTERETTE" Te Aroba): As far as we know line filters are not commercially available as-separate units, though you could quite easily have one built up. J S. (Wellington) : Full constructional * details of an aerial tuner are given in the 19388 "Radio Guide." 2. How can I reduce the heavy crashes of static without ‘decreasing volume? A. You cannot. W G.R. (Wellington): Your set has * only two amplifying valves, and so you can scarcely expect it to pick up 2ZW or 2YC at anything like good volume with a small. indoor aerial, We cannot advise readers to make alterations to commercial sets. H B, (Waikato): The circuit of your * receiver- is contained in the 1931 volume of the "Official Radio Serviceman’s Manual." W F.C. (Wellington) : I have just been * given a variety of components, a list of which I enclose. What set could I build which would incorporate most of them? A.: Wither the "Skyline Five," a t.r.t. set described in the June "Radio Times," or the. "Hight Star Five," a superhet. described. in the August "Radio Times." "YY ANK" (Eketahuna): Can a pick-up ’ be employed with a two or threevalve amplifier, and, if so, where can I obtain constructional details?

A.: Yes, A-2-valve amplifier was described in -the 1931 "Radio Guide." Alternatively, you .could use the. audio section of the "Overseas Four," which appeared in the June "Radio Times," . 2. Could I construct the a: .plifier from parts taken from my five-valye commercial battery set? A.: Yes. Both transformers you mention would be suitable. Note.-Of the valves you have on hand, use the B605 in the last stage and any one of the others in the precéding stage. The pick-up. mentioned would be quite suitable, mo HA H, (Wellington): Would reception ~~" be better with a cage aerial than with the ordinary "L" type, both aerials being of practically the same length and height? , A.: Signal strength from distant stations would.possibly be a little Stronger, thought selectivity would suffer, 2. Would the improvement, if any, be equal to adding another yalve? "AV: No. : D E.B.. (Christchurch): You can con- * nect the microphone through a transformer to the pick-up terminals of your set. Of course, you will need to place a battery in series with the primary winding and the microphone. "(pPAWA" (Christchurch): I can pick up harmonics from 3ZM on my allwave set on approx. 1400 k.c., 1860 k.c., and 1110 k.c, and also two harmonies from 3YA, A.: These are repeat points, not har. monies, and if your set is ecorrecily aligned they cannot be eliminated. "DENTAFORM" (Dunedin) : The "Diode" Six is as sensitive as the average set with three stages of r.f. "GENERATOR" (Canterbury): 1 intend to build a short-wave receiver and transmitter. Would a 6-volt car generator driven from a windmill be satisfactory to charge the batteries? A.: Yes. You will need to arrange your wet "B" batteries in 6 volt blocks, paralleling them for charging purposes. 2. Is any other apparatus necessary to control the current?

Information Coupon (To be used with all requests for information.) Name of set see wn vesccesscecosanss Mode} Toe PACT OSS OROSE BOSSES OSOOFEF Name svevecee eacecerceorss Address FOCOSHSSOCESESREOTOOSOEESS? tthe treet titiiiiititi iit Peereeres cr emerescescasoceseseeevencs Nom de plume ...cccvccccuccceces ' To be kept in subsequent inquiries Please Note:- . 41) Be specific ana orief, tabulating, if possible. (2). Write legibly. and on one side of the paper. ‘ . (3) We do not design circuits, (4) Limit three questions. . unless 1/- is enclosed : (5) Postal queries limit 3 queations, Enclose stamped and’ addressed envelope and 1/- fea,

Ac* An ‘ainmeter™ and a "heavy~ duty~ rheostat to control the charging current. Some means should also be provided for cutting in the generator when the charg: ing rate becomes sufficient, and also. for: cutting it out when the charging rate becomes too high. "PDADEX" (Waitara): I ean. log only one American station, KFT, which comes in at full volume. Should I be able to hear more? A.: Yes. It is chiefly a matter of knowing when and where to look for them, Study the dx pages. 2. Reception from all stations has lately become distorted. A.: Have your valves tested, and the alignment of your condensers checked. Possibly the trouble is due to unfayourable reception conditions. W. (Auckland): Could I use the © method of volume control employed in the "Quality Six" (described in the 1933 "Radio Guide") in a set employing 282 r.f, valves? A.: No-=these valves are not of the multi-mu type and bad distortion would restilt when the bias was increased much over 1.5 volts. Note.--The plate of the English screengrid valve is connected to the cap, but in the American type it is the grid which is taken to this connection. Co el F. (Cambridge): The plates of my * 980 rectifier become red-hot. Could you tell me which condenser has broken down? A.: One of the filter condensers, more likely that before the smoothing choke. 9. The rf. filament voltage has dropped. Why is this? _ A,: This is due to the very heavy load thrown on the transformer by the broken down filter condenser. 3. Could you outline the method of aligning the condenser gang of a receiver, using a milliameter? A.: First of all connect the milliameter in the detector plate lead. Then tune in a station somewhere near the middle of the band, say 38YA, and adjust the trimmer on the detector section of the gang for maximum signal. Repeat the process with the second and first r.f. sections in that order. "OMSK" (Whakatane): You would need to pass a special examination, the Broadcast Operators’ Hxamination, before you would be permitted to operate a station on the broadcast band. Full partieulars may be obtained from the Post and Telegraph Department. 2. What would be the approximate cost of a 15-watt amateur transmitter? A.: About £8 to £10 for the transmitter only. Note.-1400 volts is far too high for 212 D’s employed as oscillator. Do not use more than 1000 volts. Modulating the amplifier, the power of your proposed transmitter would be from 15 to 20 watts. "Buppy" (Christchurch) : Since fitting new valves in my 5-valve commercial T.R.F. set, noisiness and instability have developed. A.: Evidently the special control employed in your set has become defective, ‘and the r.f. valves are now operating without bias. This would explain the broadness of tuning of which you complain. 2, How can I re-align my set? A.: Tune in a station operating somewhere near the middle of the broadcast band and turn the volume down. Then with a screwdriver carefully adjust the trimmer of the detector section of the gang ‘until volume is greatest. Then do

"likewise with the second r.f, trimmer, and--finally the first. A "peak" position should be obtained with each trimmer, i.e,, when turned a fraction either way, volume. should diminish. If it is found that one > trimmer screws right in or out without giving a peak, screw the other two 4 turn or so in the opposite direction and repeat the process. 3. How is volume controlled in my set? A.: A special type of volume control. is employed, which operates as a poten--tiometer across the first r.f, primary and also varies the bias on the rf. valves. EPRW’S HOPING" (Wellington): Between 4.30 p.m. on Sundays, when 2VA. closes down, and 5.30 p.m., when 4YA commences the children’s session, I cannot pick up any station at all, even

with the volume control full on. From 550 kc, to 950 k.c. all I can hear is a slight hum, From there on to 1200 k.c. static and other noises are heavy, but from there on to 1500 k.c..a hum is all that can be heard. A.: We have tested out the particular model you are using and found it a splendid dx set. It appears almost certain that your set is badly out of alignment, and we suggest you get in touch with the local agents. " ©." (Ngaruawahia): In "ham" par°Jance, 73’s means "best regards," and 88’s "love and kisses.’ There are only three figure abbreviations used, the third being 99, which means "keep out." T ©. (Christchurch): Do not earth your ® second aerial when it is not in use. To comply with the Underwriters’ Regulations, however, it must be eonnected to a lightning arrester. ; "PUZZLED" (Livingstone): The type 19 valve will not be available in New Zealand for several months yet, so your best plan would be to use two 230’s instead. The switch and battery cable could be shifted, as you suggest, without affecting the performance. The speaker you have ean be connected directly to the output terminals, If you have difficulty in making the set oscillate, reduce C6 to .00005 mfd. "AFOGUL" (Hokianga) : I have a threevalve battery set: Can I connect the headphones and speaker to the set without damaging it in any way? A. Yes. "& UDIO" (Auckland): X wish to add a stage of audio to my 1-valve set. What would be the best ratio for the transformer? A.+.5 to1. or with a good quality transformer,. 74 to 1.

2. What-"B" voltage would. be required to operate a small cone speaker? ~ A.: 120 to 185 volts. 3. Does oscillation affect neighbours’ reception to any extent if the set is operated on an indoor aérial? A.: Yes. A broadeast set such as your’s should never be allowed to oscillate under any conditions, BADER" (Horotua): My reception is spoiled by crackling and hissing noises caused by generators and motors in the locality. At times it is almost im- . possible to use the set as the noise drowns all reception. Can this be rectified? A.: We doubt it. The articles on eliminating power interference published — in the "Radio Record" dated July 21 and July 28 may help you. "GPARKS" (Rangataua): Would a 201A be suitable to use in a onevalve amplifier to be added to a erystal set? A.: Yes. Your circuit is correct. Note: You will find that sensitivity would be slightly improved by tapping the erystal down the coil in the way shown in the circuit of the "Seleatra" erystal set, described in the August "Redio Times." NAST COAST" (Gisborne): Use 4 32’s, 2 30’s, and 133. A two-volt 40 -amp-hour accumulator will be satisfactory for "A" supply. Q1GOA. (Auckland): I am enclosing a diagram of my two-valve all-wave set. What is the maximum voltage for B+?

A.: You ean apply anything up to 150 volts, though you will probably find the set will operate best with 45 volts, 2. What should B max. be? A.: 120 to 135 volts, Note: Your cireuit is quite in order, though you will probably find that reception will be improved by connecting the grid leak from G to A-- instead of across the grid condenser, "[EJNTUNED" (Timaru): Would it be possible to add a stage of untuned sereen grid r.f. to my commercial threevalve battery set? A.: Yes, though it mean rather expensive alterations to the set. ap HH. (Taihape) : I have a seven-valve commercial battery set which oscillates rather badly. A.: We suspect you are using the wrong type of valves in the r.f, stages. The set was designed for 201A’s, 2. I have constructed the wave-trap deseribed in the July "Radio Times," but cannot get it to operate satisfactorily. A.: If the condensers of your set are badly out of alignment the trap will certainly not make much difference. G. R, (Nelson): How can I prevent the whistle which results when two stations operating on practically the same frequency are tuned in? Would a wavetrap be of any assistance? A.: No. This phenomenon is’ called heterodyning, and is caused by interference between the two carriers, H L.M. (Milton) : What is the approxi- * mate trade-in value of my set? A.: It is impossible for us to tell you. Any dealer would be pleased to give you the information. 2. Which is the better for. short-wave reception, an a.c. all-wave set or an .a.c. set employed. with a converter? . A.: This depends. on the type of set. If both are well designed and constructed : there would. be very little to choose be tween them, o

we . Two Fine Sets ‘The "EIGHT STAR FIVE" and the " SKY-KING SIX" are described in the August ‘‘Radio Times" Get YOUR Copy Now ! to ey