QUESTIONS AND ANSWER

Radio Record, Volume V, Issue 14, 16 October 1931, Page 12

QUESTIONS AND ANSWER

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, circuits 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 cannot be regarded as a reason for its not being used. Address all queries, The Technical Editor, Box 1032, Wellington.

R A.8. (Christchurch): We are send- °® ing you under separste cover full particulars of the DX Club. 2. The numbers on iny dial go from 0 to 100. How can I find out the kiloeycles and metres they represent? A.: It is yery difficult to do so from a dial that is reading from 0 to 100. Your only plan is to prepare a list of the stations you get and their frequencies. Then, for stations in between those you have already listed, you can more or less estimate the frequencies. There is no direct way of telling unless you plot @ curve. 8. The distant pole of my aerial is 40 feet high, the lead-in 30 feet. The total length, including the lead-in, is about 90 feet and crosses an iron roof most of the way. Would it improve matters if I shortened the aerial 10 te 16 feet and avoided the roof? -A.: Theoretically, yes. Whether it would be any better in practice is another story. It would certainly be well worth trying. P A.B. (Auckland): I wish to build a * one-valve amplifier and have 201A‘'s and power valve. Are these suitable? As Yes. Use one of the 201A’s. 2. I have a 6-1 ratio transformer. Is this suitable?

A.: Yes. We do not happen to know the transformer, however, and cannot tell you the markings. Your sketch is correct. V OLTAGE (Otago): Would I get better results if I used a pentode in the Jast stage and coupled it to an inductor dynamic speaker? A.: It is very hard to say whether you would get better results or not. If you use a specially matching transformer you certainly would get better results. If you didn’t use this transformer the ehances are that your results would not be any better than they are at present. The péntode is a wonderful valve, but needs to be specially matched to the speaker to get the best out of it. An article on matching the pentode to a speaker appeared in the "R.R." a few months ago. You could have a speciallycoupled transformer made to your requirements. The inductor dynamic speaker will give you better tone than the one you are using at present. RATERFUL (Oamaru): I have recently constructed the "Outspan Five" and have had good results with it. In the. last stage I am using P625. Is this JI.F A.: P625 is the equivalent of UX245. If you have available 250 volts you are

getting the best out of your set. If not, the value is far too big P625A would be better. 2. I am troubled with a whistle. A.: This is due probably to coupling between the stages. Use a choke ani by-pass condenser in the lead to the plates of the rf. valves. The circuit we show here for a filter in the detector circuit will possibly eliminate some of the

trouble. You use two small condensers on either side of the existing choke. 8. How could I even up my dials? Dunedin comes in at 90 on the ist and 2nd dials and at 80 on the next. A.: You need a few more turns on the third coil. Try five turns extra. You could make a soldered joint; there is no need to rewind the coil. BANIO (Hawera) : I have an American set using A615 first and second r.f., and detector A609, first a.f. B605 output. Could you suggest a better combination to bring in more volume and distance? A.: Your combination is really quite ood, roviding your set ean be neutralised with A615 in the first and second r.f.’s. If you can do this then you are getting the maximum from your set. Répro (Bay of Plenty): Why cannot I get stations under 330 metres? 2YA comes in‘all right, and also 1¥A. but nO others. : It seems as though when you turn below 880 metres the vanes of your condensers touch and consequently shortcircuit, Hxamine the condensers, turning them so that the dial reads below and above metres, and note what hap- pens. The valves you are using in the audio stage are quite satisfactory, and it would be hard to suggest a better combination. ONE, DIFFERENTIAL (Oamaru): wish to construct the One for short-wave. Where could I get a description of same? ‘What would be the total cost? A.: Build the "Sparrow Hawk One" deseribed in the 19381 "Gu ide," using a .0001 tuning condenser (this is for shortwave only). The total cost with accessories would be £6 or £7. Me. (Picton):. What is the best combination of valves for a B.D. 4, working on an eliminator d.c. supply of 90 volts? A.: We can only give you the type, you must choose the individual valves yourself, Use type 221 in the r.f, and first

audio stages. A special detector of the O15 class, and as audio, a valve of th G05 type. 2. A slight hum at times comes from my, dic. eliminator. : If it is only spasmodic, it is due to on the line, You ean try only an extra filter choke and condenser. We would advise you to look’ uj the articles on the d.c. eliminator which were pubished in the "Radio Record" some time ack, K OOKABURRA (Napier) : I wish to convert the "Sparrow Hawk One" into a short-wave adapter for an eightvalve super heterodyne. What = circuit could I use? A.: You eould use the parts of the super-heterodyne circuit described in the 1931 "Guide." PUZZLED (Wellington) : I cannot get the "Differential One’ to oscillate when using an indoor aerial. Results are quite unaffected by the reaction condenser. . A.: This sounds like trouble in the condenser itself. Use the phones and cell method and test for short circuit between either of the two fixed plates and the moving plate. Also make quite certain that your connections are made to the right terminals. 2. Could this set pick up some of the Wellington amateurs, using an indoor aerial? A.: Indoor aerials are not particularly satisfactory. You may, however, be able to pick them up. 3. If you substituted a grid leak and condenser for the crystal, we think: you would do better. How ever, the circuit is not a good one. Why. not build up a circuit such as the all-wave "Sparrow. Hawk," and then you would be more certain of results.

‘ (Miramar): On my crystal set I ~* have to tune to 180 to get 2Z2W faintly. 2YA comes in best on 45. A.: You have far too many turns on the secondary coil. Take off ten to fifteen at least. 2YA should come in at about 10 on your dial and 2ZW would then be at about 185. Do not take plates from the condenser. Damage the coil-it is cheaper. OOK-UP (Matamata): We do not ~*~ happen to have a copy of the "Radio to which you refer. If you must build circuits that you cannot complete from overseas magazines, we are afraid we cannot help you. 2. Is there any means by which I can match r.f. transformers and bdnd pass titers, without using expensive apparatus A.: The construction of rf. transformers wus described very fully by ‘"Cathode" some months ago in the "K.R." We would advise you to look up, this article pw (Shannon): You have cer- , tainly been unfortunate with your However, why don’t you try’ a really good make, as that will, we think; be the only solution to your trouble? There appears to be nothing wrong with your hook-up, and it is only a matter of striking a reliable transformer. We think if you communicate with the New Zealand agents for the transformer of your shortwave set which burnt out and explain the position, they may do something for you. ‘Tell them how long you have had the transformer. YNAMO (Waitomo Caves): The yolume control on my set is very unsteady. As soon as it is turned up a little the sec begins to oscillate. A.: The set is not neutralised properly. What valves are you using? You should be using 201A or 221 in the firsz two stages, and then have the ueutralisjing condenser adjusted to balance them hp. You will then find that that trouble will disappear. 2, A frying, bubbling noise is very often apparent in my set. A.: This may be due to the set not being neutralised, or it may possibly be a burnt-out transformer. To test the transformer primary, use the phones and cell method described in "Questions and Answers" last week. . 8. When building the "Outspan Five" regeneration coil, would it matter if the tickler coil was on a different former and put in a different place? A.: Decidedly yes. The tickler coil must be adjacent to the secondary coil if regeneration is to take place. (jOLLs (Owhango): In replacing the / present r.f, valve in my receiver with a screen-grid, can the original coil be used? A.: Not without being altered. Why not add an extra stage of screen-grid as described in this week’s "Radio Record"? Sf you want to instal the screen grid without, the extra stage follow the lines laid doa in the constructional section this week and couple the screen-grid valve directly to the detector. 2. Can I retain the tickler coil or must it be replaced by a differential condenser? A.: There is no necessity to replace it with a differential condenser. You need alter the radio section of your set only. R LA. (Dunedin): The sub-panel is * the same as the base. This consists of a sheet of aluminium, 18 inches by 12 inches, turned down 1 inch all round. A further sheet of aluminium 12 inches by 7 inchés must be used to separate the

radio stages as is shown in the sketch on page 29. Wood is not used in an electric set, i+) Af P, (Dunedin) : I am making the "Out- * gpan" with six valves and do not intend to use regeneration. How can the coils be matched to the condensers? A.: The easiest way is to consult a table such as that appearing in the 1931 "Guide," and you can then get the coils for any gauge of wire and any former. If you start to work these things out by formula you will have a sheet of figures and will not get anywhere, unless it is muddled up. Once you have the size of the coils worked out, you fit them in your set and, when the set is operating, finally balance them up. ‘This is done by tuning to a station at about the middle of the dial and slackening the condenser shaft. Then take the first radio condenser and move the variable plates slightly to see if the signals increase. If the signal can be improved, that coil is not matched to the others. Should the plates have to be pushed in slightly this coil has a lower inductance than the remaining coils. Leave it in this setting and go on to the next coil. Adjust this one and you will probably find that this condenser does not have to be so far and remove a few turns from the coil associated with it until the two condensers are at the same setting. Go right through the four stages until all the condensers line up nicely, then tighten the little serew holding them to the shaft and they are matched as near as possible, A .00085 condenser would require a coil of 87 turns if wound with 26 wire on a 2 inch former, 1S DOUBT (Lower Hutt); I want to use a power unit and battery charger as described in May of this year, into an "A" ond "B" eliminator. Can I use the "A" supply suitably smoothed? A.: Yes, you will need a smoothing choke comprising 300 turns of 18 d.c.c. wire on a core 1} inch. The gap should _ be 3/16th. ‘This is choke "K" "Radio Record" standard, as published in the 1931 "Guide? An electrolytic condenser must be used across the winding. 2. Could the same rectifying valve and resistance lamp be used ? A.: Yes. yr (Manurewa) : I am troubled with transmission hiss on an a.c. set employing the latest valves. Are the valves at fault? A.: Lransmission hiss is due usually to the valves themselves, The combination of valves you are using is one of the best und we would suggest that you get in contact with the agents who sold you the set. Probably the replacement of one or perhaps two valves would overcome the diffieulty. Tv A. (Morrinsville): Do you know anye one who has logged more than 40 stations on a one-valve set? A.: Ask the DX Editor. He will probably tell you that there is a man in Palmerston North who has logged Burope on @ one-valver-or perhaps he won't. 2. During rain I am troubled by a loud sizzling noise in the phones, A.: This may be due to a power leak, or possibly to your aerial finding a short circuit to earth, Examine your aerial installation very carefully. Make certain eat trees are not coming into contact with _ 3. Would the addition of another valve improve the volume and assist in bringing in distant stations? If so, what would be the approximate cost? A.: It would certainly improve the volume to be had from your set, and does assist in bringing in the distant stations. The cost would be something like £2.. mt) a We

ISGUSTED (Whangarei): I have built the "Kestrel Three" and cannot get it out of oscillation, .I cannot reconcile your sketch of the coil and the sketch in the book. A.: Had you examined them a little more closely you would have seen that they were both the same, with the exception that the artist, in drawing up the picture of the r.¢, coil, has shown the tuning condenser upside down. ‘That, however, is only a very small detail. You will see that the top of the eoil goes to earth, and to the moving plates of the tuning condenser, The bottom of the rf., that is, the grid pin, is connected to the fixed plates of the tuning condenser (or the .0001 condenser, which is its equivalent), to the grid of the valve, and to one of the sets of plates of the midget condenser. If you will make sure that your connections are right, you will get the set out of oscillation all right, but you must have the high potential end at the bottom of the coil. We made that point very strongly in the article. For the

sake of clearness in making our diagrams, we took the grid direct to the fixed plates instead of through the .0001 mfd. condenser. Of the two sketches you have submitted for the connection of chokes, the first one is right, as is shown in the book. ‘There is no question about which we intend; it is shown clearly in all three illustrations. Very many have this set working, and no one yet has complained that the text and the drawings fail to agree. All your trouble is possibly because you have the high potential end at rhe top of the coil. if this is not so, then your best plan is to put a cocoa tin over the coil, and, if necessary, over the valve itself. BAe (Auckland): I recenttly purchased a five-valve set, complete with 6volt "A’? accumulator and 90 volts "B." Should I be able to get the Australian and foreign stations? I am using 221’s in all stages.-Yes. 2. My aerial is 36 feet high, but doubles back upon itself{-Your aerial should be quite satisfactory, although we notice that at one point itis only 20ft. from the ground. This is a bit too low. Cannot you get it a little higher. 3. Would it be possible to convert the set into the "Outspan Five’? If so, what would be the cost? And where could I obtain the necessary particulars for the "Outspan" ? A.: The "Outspan" was described very fully in the "Radio Record" a little while back. A few copies are still available. It should not cost you very much to convert your set, probably only the cost of the new coils and the screen grid valves, a matter, say of £2 or £3. kK (Naseby): My six-valve commercial set has developed a decided whistle. A.: Whistles can be caused by many reasons. Possibly it is due to the valves ageing or the set requiring re-neutralisa-tion. If you do not know how to go about

this yourself, tt would be wise to get & friend who knows something about the set to do it for you. The job is really simple, and was described in last week’s questions and answers. It is, however, a case of locating the neutralising condensers, which are usually near the panel. Another reason for squealing can be a run-down " pattery, a defective "A" or "C" battery, OF both, and long leads to the "B" battery, A microphonie valve can also cause a cer tain amount of whistling. 2. Ig it better to have an aerial running north-south, or east-west? A.: The direction of an aerial has very little to do with its efficiency, providing it is of the normal "L’" or "T" type. GPARKS (Carterton).-I should like to know the number of turns for a broadeast coil to be wound on a Colvern coil former? I am using a .0005 for tuning. A.: Use 26 gauge d.s.c. wire and on the secondary wind 65 turns. On the primary 20 turns, and on the tickler, if you are using a .00025 eondenser, 30 turns. The tickler can be wound with a finer gauge wire, say, 28, 30, or 32. 2. The two audio valves have the same plate and grid voltage. Should this be so? A.: No; the second last valve should not be biased. It is quite in order, however, to use the same plate voltage on this valve ag on the last, If the voltage is high, that is, over 90, a small bias of 14 volts should be applied. You need not worry about trying to put a lower plate voltage on the PMi. We have tested the set you speak of and have it perfectly satisfactory. .Of the other makes you mention, some of the sets are made in America and others in Australia. LENCAIRN (Auckland): How is it I ean get Christchurch and Sydney bet ter than Wellington? A.: It may be either your locality or 2 peak in your set. Some sets are more sensitive to certain frequencies than to others. This would account for the re ception of some stations more strongly than others which are nearer and more powerful. 2. What is the best method of padding a transformer which hums? A.: Padding should not be necessary. If a transformer hums it is an indication that either the insulation between the laminations is bad, or that the bolts need tightening. If you have to pad it use stalloy and jam in strips between the frame and laminations. W i.A. (Dunedin): I have a gix-valve e commercial set with a "B" elimina~tor, and I can receive certain local "B" class stations on three points of the dial. The set is obviously not oscillating, as I can put my finger on the aerial terminal and there is not a click. A.: It is not always possible to tell by this means if your set is mildly oscillating (it would not disturb your neighbours). It is possible that the strong carrier wave of the local station is causing beat notes which are interfering with your set. Other than this, it may possibly be reflected frequencies, , X14W (Pahiatua) writes to say that he has found in the two sets he has had that PM6 makes an admirable rif. valve. In reply we would say that, although it is an output valve, it sometimes goes well in another portion of the set, ie., as detector. If used without bias, it will place a fairly big drain upon the battery. It cannot burn out any transformers in the radio stages beeause there are none there to burn out. Ue states that he has constructed the (Concluded on page 29.)

Questions and Answers

(Continued from page 13.) "Sparrow Hawk" adapter, and found that, although it gives good results on a trans-former-coupled set, it remains silent when plugged in to a resistance-coupled audio. The reason for this is that sufficient voltage is not getting to the valve to make jt oscillate suitably. The best plan theu would be to incorporate the adaption shown for plugging in to the gramophone socket and then connect with the grid of the first audio, Gtatic (Westport): Would it be possible to add another stage of rf. in front of the "Ranger Three’? Also another stage of af. after the detector, using 201A in all stages?

A.: Yes, it would be quite easy to do so. Use exactly the same hook-up’ as was illustrated in the article. You could use 201A’s in all stages, but you would not get a very good tone if you used that valve in the last stage. It is purély a general purpose valve, and in the last stage should be replaced by a high-gain power valve. It would be well worth making up. . INTER BOY (Bay of Plenty): You can improve upon your combination of valves by using the new 221 valve in place of the 201A. Use the same make throughout, preferably a well-known one. In the last stage use a high-gain power valve suitably biased. The 201A valves are not hard on "A" or "B" batteries. A short-wave adapter should work satisfactorily with your set, and it would not be necessary to build a special short-wave outfit. We are referring your log to the DX Editor for criticism, pD™ (Mataura): My set has recently commenced a rumbling noise which makes itself heard on frequencies over 800 kilocycles. A.: Your set is out of balance. It is possible that it may be overcome by trimming up the condensers, but we think that a bias resistance in the first stage has petered out, or the rectifying valve may be fone. How long have you had the 2, Are the valves the best to use, or can they be improved upon? A.: In an ac. set you have really very little choice except selection between the various makes. You must use tho type originally used in the set. 8. What is the best height and length of an serial for this set? A.: It does not require any special aerial. Take the usual one, about 30 fect to 45 feet high and 100 feet long.