Questions and answers

Radio Record, Volume IV, Issue 37, 27 March 1931, Page 13

Questions and answers

IGHT (Christchurch): I have built the L.W. amplifier and used high quality resistances, but one of them heats, but does not smoke or show any visible signs of overloading. Is this in order? A; Normally, the ‘resistances do not hea? if.they are of sufficiently heavy wire to carry the current.- When a resistance heats it is apparent that it is not able to pass the current required. In your case providing the set works all right and the resistance does not smoke, it is quite in order. 2. I am using a crystal set coupled with a transformer and every time I make an adjustment the set squeals. Would a carborundum crystal be better? A.: To be quite candid we have done very little experimenting with a crystal in front of the L.W. We tried it out and experienced the same trouble you speak of, and so on the local station we recommended the ordinary tuner, while, if extra power is required, an extra hf. stage. We regret we really cannot help you much, especially if you are using a ‘high grade transformer and a good crystal. Probably the carborundum would be the better. ™~ \uomry (Stratford): I have-.a 18 late midget condenser with a capacity of .00025. If I remove the plate until I have 5 what will be the capacity of the condenser then? A.: About .00001, but it is difficult to gay unless you give the size of the condenser plate. The same applies to the other condenser you mention, though probably the eapacity will be very near to Quality (Devonport): I am planning a new sg. 4-valve set, with quality as my main object. I was intending to use push-pull amplification, but after reading the pentode articles in your paper my attention has been directed toward the pentode valve. Which do you advise to work directly into a dynamic

speaker-two 405’s in push pull or one audio and a pentode? A.: The two B405’s in push pull would give a greater undistorted output than the pentode. If, however, you took the trouble to match up ‘the pentode as described in the article you would probably get a greater amplification at less cost. 2. What are the disadvantages of using a trimmer with ganged condensers? ‘A.: None, except that -the trimmer means an extra control. V R.H. (Auckland): I have very old *bright emitter valves in my set. Would reception be jmproved by modern ones with 30 volts on the detector and 20 on the audio? A.: If you are using true bright emitters your set is very old indeed, for these went out of fashion eight or nine years ago. Are you sure the valves you are using are not ordinary 201A type, the . filament of which can be seen glowing through the clear glass of -the tube? These should not be confused with bright emitters, although they take a } of an amp. Modern valves would probably give you better results and you could still use 80 on the detector, but you will require at least 45 on the audio. 2. Please supply me with a formula for determining the capacity of condensers (a) in series, (b) in parallel. Ae (a) -- => — --+- .6] C1 + C2 C3 etc., or for two condensers C1C2 C1 + 02 (b) C- C1 + C2, + C08, ete. In each ease "O" is the total capacity and Cl, C2, C3, ete., the individual capacities. 8. If I used Radiotron valves what would be the best for detector and audio? A.: For a two-valve set, two 221A’s or 201.A’s or their equivalent. Note that the 201A require a + amp. filament current. J P.S. (Nelson): I have built the Dif- ¢ ferential One, but cannot get the set to oscillate. A .0001 fixed condenser on one side of the coil to earth makes the set oscillate, but does not improve reception. The set does not howl when passing a station. After the tuning condenser passes about halfway in oscillation ceases. A.: How ean your set oscillate and yet you are not able to pick up a carrier wave? Ifthe set was oscillating properly you would get a whistle when you pass a station. It is quite evident that the number of turns upon the tickler coil is too small, and it will be necessary to rewind the tickler with a finer gauge wire so that more turns can be added. 2. The short-wave coils with or without the .0001 condenser bring in several Morse stations, and the set howls in the usual manner until the condenser is halfway in. A.: It seems that you are not tuning properly. If you can receive Morse stations your set is oscillating, and you can never pick up broadcast stations in that manner. The set must be on the verge of oscillation. The .0001 condenser in the circuit and dialling must be done very slowly. . 8. Could you tell me the number of turns for each of the four coile as given

in the "Radio Record" to suit my .00085 condenser? A.: These were given at the time of the article, and are repeated this week. Your difficulty, like so many others, seems to be arising through the smallness of the differential. condenser, and the only satisfactory solution is to increase the number of reaction turns. A H. (Hokitika) : Will you design coils * for the Outspan, Five to suite .0005 condensers ? A:: The number of turns on the secondary coils is 65 for your .0005 condenser and 75 as specified in the article for your .00035 condenser. 2. Could I incorporate push-pull amplification, and is there any great advantage in doing ‘so? A.: For really satisfactory tone on gramophone and local station push-pull or petitode is the only solution. The pentode requires a specially matched circuit as described in our recent article, but the push-pull could be used with ordinary push-pull transformers. The "Gramo Radio Four" in the 1931 "Guide" should help you in this direction. 3. For short-wave reception would you advise a short-wave adapter or making coils to plug in for long and short waves? A.: The adapter. It is not easy to make plug-in coils for three stages, although it ean be done. Switching in three extra fixed condensers and chang-' ing three sets of coils might make the operation of changing from one band to another a little unwieldy. G1GMA (Auckland): I have recently tried out a-erystal set for which great things were claimed. It consisted of a 85-turn honeycomb coil shunted with a .0005 condenser in the usual manner. Although I can get the local stations and have an aerial about 250 feet long with a good ground system I cannot get Wellington. ‘The local stations come in well, and indeed louder than with an ordinary crystal set, but the condenser has to be full open to do this. Is it that a fixed condenser would do equally well in place of the moving. coil or have extravagant claims been made for the circuit? A.: The circuit is quite a usual one and it has appeared in our columns. It is really no better than the ordinary tapped solenoid coil. We think your good reception is due to your aerial and ground system, which is quite effective for a erystal set. The fact that the stations come in best with the condenser wide open indicate that the coil is too big. The number of turns should be reduced to 30, but you might, if this is not convenient, try the effect of a .001 fixed condenser in series with the main tuning condenser to reduce the capacity. 2. Have I gone to unnecessary expense with regard to the condenser, which. is a first-class one? A.: You would probably have obtained very good results with an ordinary condenser, though there is no question that it pays to install the best of components when a first-class job is desired. 8. Could you suggest any variations in the way of parts or a change in the eireuit? A.: No; you appear to be getting results as good as anyone can expect with a erystal set. It is possible to pick up Wellington on such a set, but much de-

pends upon location and upon the aeri«l and earth systems, and indeed, upon the crystal itself. As a matter of fact, the crystal to which you refer is quite readily obtainable. ae [YROIST (Auckland): I enclose the diagram of my set to which I wish to add another valve. What is your opinjon of the circuit, and can I add the extra stage or would it be better to construct another set? Oscillation usually comes in with a decided click and hand eapacity is bad when I attempt to adjust the midget condenser in the aerial? A.: The circuit is the Reinartz type, but the Schnell is usually considered better as regards hand capacity and oscillation. The plate of the valve goes directly to L2, the reaction coil. The other end of the reaction coil, instead of going to earth goes to the radio frequency choke. From this point also a wire goes to the fixed plates of the variable condenser, the moving plates of which are connected through the small condenser Cd to earth. To prevent hand capacity the midget condenser should be placed at the back of the set and the aerial taken directly to it. You are probably introducing stray capacities by taking your aerial across the set to the panel. 2. Is there any way of overcoming harmonics? A.: Unfortunately there is no satisfactory method of doing away with them, for they are omnipresent, as other waves, and are as liable to be tuned in. AITOA (Nuhaka): Which are the correct valves to use in my set? A.: Four 201A’s, or 221’s, with a B405 type power valve, 2. Would I get more volume by using a power valve?

ORRESPONDENTS 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 ..rcsseccccoscvevscaves Number of Valet ..coccccsoevesons Name Address SHC TTSHTTHOKOSHSTSSHSHHESSOCSLES SOC COHOTHS OS CORRE ODES HHETES F808 80008 eo oO OSSIDS ESS SOD OSIFSEEHES OO COPE ETH ROO AES SOSH SHST HS HOHSLESSETEHS Nom de piume Cote ee reessresesens® To be kept in subsequent inquivies. Date POTTTTTT TTT TTT Please Note:- . (1) Be specific and brief, tabulating, if possible. (2) Write legibly, and on one pide of the paper. : (3) We do not design eircults, .. but aceept 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 specifications cannot be supplied without a specialist’s fee. ,

A.:. Not unless it was one of the pentode type. A power valve is designed to give greater undistorted output; in other words, to give you purer music, usually at the cost of a certain amount of yolume. ‘8. Would it be necessary to add an extra battery? A.: It would be better to use 135 volts, but not altogether essential, You would need two © batteries, but the life of these is very long, and they are consequently quite inexpensive, BEAVER (Pahiatua) : Should a Beverage aerial run with its full length between the station to be received and the set? A.: Yes, results are better. 2. Is galvanised iron wire of about 14 gauge suitable and as good as copper? It would not be as good as copper, but it would be quite efficient. 8. Does it matter if the aerial sags a little between the poles, and does it have toRe exactly the same height all the way? -No. _ 4, 1s eight to ten feet from the ground as good as 16 to 18 feet? A: Better; the latter is too high. W P. (Devonport): I have made a ’ * four-valve short-wave set, using .00005 variable condenser. Can you supply specifications to tune to 100 metres using valve base coils?

D C.W. (Lower Hutt): I have a com- * mercial set with reaction, but cannot get other New Zealand stations at loudspeaker strength. Is there anything I can do to make the set louder? A.: It is rather doubtful, and we would not like to recommend you without having tried another stage to your set. It might be worth trying. if you could get the loan of the parts, C ©. (Westport) : My set oscillates very * badly. What is the remedy? A.: Your details are very meagre. Unless you tell us something about your circuit we cannot help you other than recommending a different detector, a variation of detector voltage, and a different grid leak. 2. The stations are all confined between 0 to 50. Could they be spread out from 0 to 100? __ A.: Yes, by removing some of the ‘turns in the coil, or by using a .001 condenser in series with your present one. 8. The first hf. condenser does not keep pace with the others. Is this due to a broken-down fixed condenser? A.: No, it is due to aerial damping, and is not uncommon.

R C. (Nelson): I have a five-valve bat- * tery set, and would like to know ¥ the valve combination is O.K.?-A.: es, 2. Is 15 volts bias correct?-A.: Yes. 3. Who are the N.Z. agents for this set? A.: We do not know. 4. In your opinion is it a good one? : We know nothing whatsoever about it. 5. I know of only one other owner of a similar set, and we have both had the same trouble; the volume control gives out. A.: Probably a manufacturing defect. A radio technician could repair the set. .6. When the set: is tuned to some of the lower dial readings, and I put my hand over the reaction the set howls, whereas on some of the other lower dial readings, the music will fade. What: is the cause of this? A.: It is hard to determine without an actual examination of your set. However, try reducing the detector valtage. RONTAY (L. Hutt): I have constructed the Night Hawk Two, and am more than pleased with the quality of reception from 2YA. However, ‘the set will oscillate only when the tuning condenser is full open. A.: Your differential condenser is of slightly low value. Try placing a .0001 fixed condenser in turn across the one and moving two fixed sets of plates. Otherwise increase the number of reaction turns by 10 or 15. oJ ACKO (Greymouth): What material do I need to charge a three-valve Courier radio set? . : Your question is not very clear. If you want to make a dc. battery eliminator, you will find that instructions have previously been published in the "R.R." Please let us know a little more clearly what you require, and we can advise more fully. "ROTORUA. -I have a six-valve commercial set. I get better results by replacing the detector with an A615. Would it improve the set further ' to substitute equivalents: for all the valves? A.: With the probable exception of the power valves, no. A high-gain: power valye could be used. 2. Would you explain ‘the Beverage aerial?

A.: This has been fully explained in recent issues of the "R.R." It is an aerial erected’ about 10 feet from the ground, and is about 800 feet long. The distant end is connected to earth through a resistance of about 700 ohms. The wire need not be ordinary aerial wire, but may be fencing wire or the like. 8. I can get KGO clearly in the evening, but no other American, except KTM. Can you explain this? A.: It cannot be explained other than by your location, which may be particularly favourable to the frequency of KTO. BROWNIE (Wellington): I am using’ a B.D. cireuit,:and have spare 227 valve. Is it possible to add another stage of r.f.? A.: Yes, quite. A circuit is published herewith.

ALE.-Is the use of a fuze in B- an effective substitute for a stvitch? No. The fuse is a safety device, and is not intended to be used to cut off the set. 2. Latterly I have noticed a spark when adjusting the lamp, and I cannot be certain that semething undesirable is not happening. A.: If, as it appears, your lamp is acting as a fuse, then you may control the "B" current by unscrewine the lamp. You may’ possibly notice a small flash when doing this. Probably there is nothing wrong in your set otherwise after the set is turned off, with the filament switch the lamp would continue to glow or the spark would be noticeable if adjustments were made. The presence of this spark would indicate short circuit within the 5 ; 8. If I approach the set with my hand a noise which often appears on certain stations is modified. A.: Bither the set is oscillating on these high frequencies or when tuned, the condenser yanes touch. If the set is oscillating it will be necessary to have the set reneutralised if it is of a neutrodyne type or use new or different valves. It appears, however, to be a ease for qa radio technician to attend to. Look to your by-pass condensers between B- rf. and earth. If they have gone, this would account for your trouble. In any case, if they ’are not present, a .5 or 1. mfd. between B + rf. ‘and earth would be advisable. G L.S. (Palmerston North).-Could 1] *cut out a condenser from my circuit’ A.: Not without employing swingine coil reaction, which is not as efficient as condenser controlled. The set would not be as good as before. :

2. What are the wavelengths or tne follawing coils? (a) See. *4° Tick. 2. © (b) See. 8 » 4 (c) See. 20 » 10. ; A.: You have not stated the Presuming they are 3in. diameter and tuned with a .00085 condenser, they are (a) 15 to 30, (b) 30 to 45, (ce) broadcast. TUDE (-).-I wish to construct a "B" eliminator to deliver 180 volts at 80 mamps. The core measures 1fin. x 1.5-Sin. If I wind 1275 turns for the primary with 32-gauge wire. and 2255 turns for a secondary with 26-gauge wire, will that deliver the goods?

A.: 1125 turns of 30. gauge enamelled wire would be satisfactory for the pritnary with what you have specified for the secondary. Roughly the transformer will require 5.8 turns per volt. 8. I have been puzzled to know: where the: filament wires connect with, as the publication I am taking the specifications From do not.show where they are brought out. "A;: These things are difficult to explain without adequate diagrams and instructions, You will find in the 1931 "Radio Guide" all the information you need on this subject. L H.T, (Rewa): I made up the Daniell * cell charger as described in the "Record," and moulded my own zincs. Chemical action was ‘very fierce when I put them in the sulphuric, and now the battery will not work. A.: You should have amalgumed the zine as the instructions stated. The zine has been attacked by the sulphuria acid, the impurities have been eaten awayJand the sulphuric acid killed. Try agai but next time follow the instructions exactly. C W.-W. (Auckland): I have one p.p. e transformer: OCan-I use it in the grid circuit of the p.p. valves and couple the plates together and take them to the phones through a condenser? A.: No. You must use a special output ‘transformer or at least two chokes. 2. What variations in the coils of the Outsnan Five would be necessary to use .0005 condensers? A.: Use 65 turns of 26 de. wire on 2in. former. A B.C. (Timaru): I am using Imfd. condensers in the radio stages of my lh. four, instead of the .5 snecified. Which would be the better to use? A.: 1 mfd. ave safer, but we found the set would work quite well with the -5’s, therefore did not recommend ‘the higheyvalue to put constructors to any expense. . 2. I noticed in a recent circuit the two rf. valves are by-passed to earth instead of to the 450 ohms resistance as shown in your publication. Which is correct? ’ A.: Why not try both ways? We published the circuit as we found it would work, but no doubt there are many other variations which can be applied. Perhans this would overcome. your difficulty with humming when you push up the volume, 8. I intend to buy a high voltage dynamic speaker. Where might I connect it to sight the field coil? A.: You must find out the resistance of the coil, and then connect it in the main chain of resistances in a position the resistance of which corresponds with the resistance of the speaker. If you cannot get an exact coincidence build up the extra with resistances external to the speaker. . \ MoA (Rotorua): Will my set take 180 volts? I am using B409 in the"last stage and PM 4 in the first andio. A.: B.40% is designed for 150, which you should not exceed. PM4 should not be used in the first audio stage. Use PM3 ' or its equivalent. 2. What valves do you recommend,

Feeping in sight the fact that I am 14 Ihiles from town? " A.: You have a good combination in at present, but you can reduce the filament # consumption by substituting the PM 4 by an A409 type, and if necessary the PM3 by the new .06 type of valve. 3. What grid bias should. I have on ’ the present valves?. : A.: You require 9 volts on B409 and + if you use PM 3 for second audio use three volts. NicHt HAWE (Wellington): I cannot make the Night Hawk oscillate. 2YA comes in well but at 0, that is with the condenser closed. I have tried putting a fixed condenser of .001'in series with the fixed plates, but it makes no difference. A.: You can make the ‘set oscillate by connecting a .0001 condenser from one of the-sets of fixed plates to the moving plates, or by winding 50 turns on your reaction coil. pe I find that the "C" battery chokes the,power valve, and yet, when I put anhac valve in the set, it works quite well, A,: As far as we can see there is no reason why it should do this, especially if you are using the right bias on that type of valve. As a matter of fact the valve you are using requires very little bias, only 9 volts at, 180. pét (Hokianga): Can I use grid bias on my power valves, two 603’s? A.: Surely with two 603’s, which we ' presume are in push-pull, you have grid bias? If you are not using a "C" battery then there is something radically wrong with your set. _ 2. I intend to install the Pierce earth system. Would it improve reception? A.: It would be an interesting experi‘ment, but we cannot guarantee that it would improve your reception. «1 38, Would it be possible to put a pen- . in an ordinary set? A.: It can be installed in an ordinary et merely by connecting the auxiliary grid to B+, but the best cannot be got out of it unless a special output filter as described is used. KF J. (Tikorangi) : Music from my four- * valve set is harsh and distorted. The set rattles when the volume is.turned up. I am using a horn speaker, A.: Distortion is arising probably in your speaker, as your valve combination appears to be quite satisfactory and your transformers are standard. . 2. If I changed over to r.c. amplification would I be sure of getting pure reproduction? A.: No; r.c.c. has very few. tonal advantages over a good transformer-coupled amplifier. . : z, 8. Is PM5B suitable for detection and 1.f. amplification?-Yes. °° . A. Is there a battery operated L.W. omit yet? ‘ "A.: Yes, but it requires 280 volts d.c. 5. Would the one L.W.. amplify as much as one transformer coupled stage? -Yes, more. . 6. Would I get better results with the Beverage aerial if its height were about 20 foat?

AV: If by results you mean increased noise, yes. Otherwise, no. . FFRAMBOISE (Auckland): The set when tuned on goes for a while, then stops for five minutes, shudders like Morse, and then rights itself. A.: This appears to be a loose connection or something wrong with one of the valves. Try tapping them to see if you can cause the trouble. Move your set when it is operating to see if it will stop. You are using a valve in the second last stage. This is incorrect, you should use 201A. { 2. My set is an old model, Would it pay me to change to the Outspan Five? A.: The Outspan Five would be more sensitive, and you would get better results. 3. What would be the cost for a firm to do the job?,

A.: It depends wpon what can be used from your present set. The job should cost you no more than £8 or £10, but it might. be considerably less if most of the parts could be supplied from your present set. 4, The "OC" battery does not seem to affect the machine. Why? | | A.: Providing it is not flat, your. valve is in perfect order, it is difficult to explain why it will not have any effect. Are you quite certain..it ‘is connected round the right way, and the amount of bias is appropriate? You should be using approximately 30 volts. | , Give, the neutralising instructions briefly, using neutralising condensers. : Tune to a fairly loud station and then shut off the filament current from the radio valve. Adjust the neutralis-

ing condenser until the signals. almost: or fully disappear. Turn on the filament current again, and the set is neutralised. BRASS (Auckland): Is the differential One suitable for short-wave work? A.: Yes, see a correspondent’s report in last week’s issue. ee 2. Is the coil former only large enough to fit neatly over the valve base A.: Yes. The former should be 14in. in diameter. 3. Would a compression condenser of the formo type if connected in the place of the .0001 fixed condenser be an im provement? . A.: No. It is not necessary. 4. Must I. use lowloss coils to get down to 30 or 40 metres? A.: This is not at all necessary. The coils described are quite efficient. 5. Where can I procure a design of a simple transmitter? A.: See the series of articles on "Breaking into the Amateur Game," published in the "R.R." recently. .Yurther information may be obtained from "Yandy’s Handbook," which may "be procured from Te Aro Book Depst, Courtenay Place, Wellington. 6. Is it possible by adding a coil of 250 to 300 turns on a 3in. former to pick up Morse on a crystal set?--A,:

Detector R.F. eoil. Tv, eoil Wavyeband Aerial Grid. anode, reaction, metres. 34 33 8% 34 9-12 5d 64 64 ve} 12-19 84 94 84 103 19-28 103 184 123 12% 28-40 154 204 184 154 40-B5 204 27+ 254 18+ 80-100