Questions and answers

Radio Record, Volume IV, Issue 21, 5 December 1930, Page 13

Questions and answers

M I.J. (Auckland): In winding broad- * east coils for the 1930 "Guide" short-wave set can I use 32 B. and S. wound on extended valve bases? A.: 82 gauge 1s really very small; 30 worsel be better, and we have designed co#s with these specifications. In a very short time, we really hoped to have had them this week but find we cannot, we intend to publish complete specifications for short-wave coils. 2. What is the most suitable ratio of audio transformer to use? A.: Use low ratio for cuality and high for loudness or volume and distortion. Generally speaking 34 to 1 gives the best results, SoMN OS (Taranaki): My set has been distorting on the upper notes and has survived numerous alterations in the valves, layout, ete. With the power valve I have given as much as 40 volts bias and still get distortion. The m.ampmeter still shows distortion in the first stage. If due to an overloaded detector how can this be cured without loss of volume? The transformers are 4-1 and 2-1. A.: You seem to have tackled most of the avenues that we can advise. The 2-1 transformer should be placed in the first stage and the 41 in the second. Other points seem to be too large a capacity condenser from the plate of the detector valve to the filament, or its absence. An _ inefficient high-frequency choke in the plate lead of the detector would cause loss in high notes. An anode bend detector will prevent over-’ loading in that stage, 2. I have a swinging tickler and oscillation is very violent. A.: It appears that you will have to take oft some of the turns on the swinging coil. pUZZLED (Westport) Since I have replaced my valves I can get only half the volume that I did with the old ones. A.: It sounds as though a yalve is defective. One of the batteries may be reversed, and see that the "C" connections are the right way round. If you

a still do not get results you should communicate with the agents for the set who sold you the valves, Af B.H. (Auckland): Will you design * coils for my short-wave receiver to be tuned to a .0003 condenser? A.: A complete set of coils will appear in the near future. There is no point in using a condenser as large as .U008. Far better to remove some of the plates and use one of the sets of coils to be described. RESISTANCE (Christchurch): I_recently constructed a wet "B" battery, using Edison elements. The battery runs down too quickly. I mixed the electrolyte myself, but do not know the exact proportion in which I mixed the elements. The battery charges very quickly and rises to 175 volts, but at the end of six days the voltage is down to 125, sometimes less. A.: Your "B" consumption appears to be about correct. The fact that your batteries charge up quickly point to a high specific gravity in the alkaline solution or a high charging rate. The remedy is to reduce the specific gravity and so permit the battery to take a longer charge, or reduce the charging rate, as this holds good with any battery. The slower you charge the longer you discharge, and conversely the quicker you charge the quicker you discharge.

X. (Dunedin): How many plates * must be removed from my .0003 condenser to make it ,00025?-Two. 2. Where can I obtain a copy of the "Tisteners’ Guide’? A.: Try the Te Aro Book Depot, Wellington. 8. In what number of the "Radio Record" were the particulars for coils to suit my set given? A.: They will be given again in a complete table in the near future. pur (Wanganui) : I have made up your superheterodyne short-wave adapter, but it doesn’t superhet. Should L8 and L4 be connected to earth?-Yes. 2. Would it be O.K. if I took the B+lead for the adapter plates from the cap of one of my 224 valves? A.: No; you must have a complete separate power supply for the superhet. The cap of your 224’s are the grids of the valves, and consequently should be negative. You will find the set will work

quite satisfactorily if you observe these few points. RAZDIOLO (Hamilton): Below 300 metres reception is clear and then distortion and fading occur. The set used to rumble anywhere below 300 metres, but this was remedied by sandpapering the bottoms of the screening shields. A.: It may be your down lead from the aerial is swinging or hanging loose. From the data you have given us it is very hard to suggest anything other than 2. When the pickup touches any metal on the turntable and when any weight is placed upon the turntable the _ set buzzes. A.: In some pickups this is quite in order; in others it denotes a broken cord or open circuit. 8. When the earth is disconnected the set rumbles and the stations come in with more volume.

a A.: This is because the set is then on the verge of oscillation. 4, cannot be obtained without the valves overloading. This is a new feature. A.: It appears you are oscillating, and this can be caused by a defective valve, a broken or bad connection in aerial or earth system. ook over these, partiecularly where joints haye been made, See that the grid-leak is making a good contact, and "if you can try the use of another one. LONGEARS (Westland): Would a erystal set work two miles out. of Invercargill? A.: That we cannot say definitely. Your best plan would be to write to the station and see how far they get erystal reception. Such a set should work quite well. 2. Can an amplifier be attached to a erystal set and what would be the price? A.: You can attach any variety of amplifiers to a crystal set, and a good one would cost you about £3. THTSON (Milton): Will you give me the specifications for a 2 amp. charger using a Tungar bulb? The iron to be 1iin. A.: You will find most of the information you require in either the 1930 or the "Tisteners’ Guide." The number

of turns on the secondary will of course depend on the voltage you require. You should use 18 gauge wire for the secondary. D (Blenheim) : Where could I get in- ¢ structions for making a cheap Morse eode transmitting set? A.: We will shortly be commencing upon a series of articles which should suit your purposes. 2. I have a two-valve home-made set. What would I need to make it into a three-valve set? A.: Another valve. Instructions for hooking up another one were given recently, AGNET (Wellington): Specifications for short-wave coils will be published in the near future. PE (Palmerston North) ; The "B" accumulator jin the 1930 "Quide" charges well and gives full voltage, but i¢ will not hold its charge. A.: Plates to form properly take a good deal of charging, so although this is the eighth time do not lose heart, See our replies to "Resistance." Also lok for an internal short-circuit in the battery such as the plates touching or thick sediment. QGOREEN GRID (Ngaio): I am using h a high voltage dynamic speaker from my powerpack which supplies the LoftinWhite, but there is a pronounced hum which is not present when using a magnetic speaker. How can this be overcome? A.: It seems very much as though your powerpack is not delivering the current that is necessary. It requires a very good powerpack to stand a drain of 60 m-amps at 400 volts. If the drain on your speaker were to cause a drop in the initial voltage the symptoms you speak of would appear. All the resisiances are planned out for working on 400 volts, and if you go below this the bias chiefly is altered and the cireuits become out of phase and the hum is caused. Apart from that we are at a loss to understand why your set should hum, particularly as it does not hum with another speaker. If you measure the yoltage and find it to be correct, then have the speaker tried out on another set. See our article this week on another method of connecting up the sneaker.

2. The L.W, is slightly unsteady on the higher notes. "AL: Unsteadiness in the L.W. in any shape or form is due generally to the failure of the outfit to adjust itself to the bias required, and this traces down usually to a defective grid-leak resistance in the bias supply of the 245. 8. The 245 valve passes 36 mils, when used without an r.f, choke, but with it it consumes 33 mils. How can I reduce the current to 30 mils. as per the specification? A.: Hither the voltage delivered to the 245 is too high or the main chain of resistances too low, or the bias not properly adjusted. You should try another grid-leak in the circuit already mentioned. 4, Would heavy gauge sheet metal be suitable for the tuner chassis if aluminium shield cans are used for the coils? A.: According to the dictates of theory iron shielding . is not advised where radio frequency currents abound, though probably in a ease such as this it would be quite satisfactory. W. (Gisborne) -Would you send * mea copy of the "Record" describing the way to make a good crystal set? A:: We have some descriptions ready, and they will be published in the very near future. If: you keep an eye on the paper you must see them when they come out. 2. If one had two sets on two separate aerials running to one pair of phones, would the results be better? A.: No. To get full way rectification, which, by the way, you are aiming at, it would be necessary to use a special hookup, such as was described in the 1929 "Guide." This is an experimental set. and cannot always be relied upon to give good results. So much depends upon the maximum of the crystals, the coils and the condensers. G B. (Lower Hutt).-In a back issue of the "Record" there was an article dealing with the construction of a trickle. charger using aluminium. A.: The description appeared in our issue dated November 16, 1928. It is a rather tricky circuit, and by the way it contravenes the existing regulations. Your better plan would be to make a proper trickle charger with a transformer, EGINNER (Dunedin): Is it correct to place a resistance for resistance control regeneration in the B+ lead of an adapter ?-Yes.

2. Can the resistance be placed in the B- lead when this lead is joined to A.: If you want to do this you must place the resistance between A- and B-, and'so they will have separate leads to the set. ’ 8. I have tried out the resistance control regeneration but oscillation is difficult to control. Would it be improved if resistance is placed in the negative lead? .: It is unlikely Dut it would be worth while trying. The difficulty of controlling regeneration is due probably to the design of your resistance and the layout of your set. The radio frequency choke should be between the plate of the valve and the transformer of your ordinary broadcast. On the other end of this winding of the transformer is the resistance and by-pass condenser. The hook-up is shown in sketch No. 11 in the accompanying diagram. 4. The resistance seems to be affected by hand capacity. : : You will find it will be preventeéll when you make the alterations in the circuit suggested. ! 5. Should the number of turns .on the aerial coil be altered for each waveband? A.: Yes, but the best plan is to do away with the aerial coil and bring the aerial through a condenser to the grid terminal of a coil. The aerial coil is usually about half the secondary. 6. Is the layout of my cireuit correct? A.: We do not undertake altering layouts for correspondents, for it is a big job, but you will find if you reverse the positions of the tuning condenser and the resistance, turn the coil round so that the secondary terminals are facing the condenser, and move the valve socket over you will have a better layout. The plate lead is far too long. It must be shortened if good results are to be expected. Your hook-up No. 2 is quite wrong. You are passing the current for your "A" battery through a 100,000 ohms | resistance. The result will be that the valve will not light. ANXIOUS (Devonport).-TI have built a shortwave set exactly to specifications, and can only get Morse stations. The set has been tested and found O.K. I can oscillate only on part of the dial. A.: You could try increasing the"B" voltage, as this should make your set oscillate more readily, but failing this we would advise you to get in contact with the local branch of the organisation, who

| A Dozer uses for Varlable fiigh Resislancles

put out the circuit and they can probably give you advice based upon experience, Y PHARLAP (Napier) : I am erecting an aerial as per the sketch enclosed. I would have 50ft. masts separated by 80ft., but would have to carry the leadin 7Oft. to the set. I could shift the mast to within 25ft. of the set, but the staying would be more difficult, A,: The aerial in its present situation would not be as good as it might be. long aerial lead would have a detrimental effect upon the signal strength to be received. Your best plan would be to put the mast nearer the house and the more distant one in the position now occupied by the nearer one. You would find if you totalled out the length you would have just about 100ft., which is the maximum length for a set using eight or nine valves. 2. What gauge wire do you suggest?{7/22 enamel, é: Would an ordinary insulated wire h as that used for house lighting be suitable for leads in and out? .: No, you should insulated 7/22. The enamelled would be quite satisfactory if you keep it away from the building, Al B.G, (Lower Hutt): The short-wave * adapter in the 1980 "Guide" does not work on telephone, but is quite satisfactory on Morse. Telephone carriers can be distinctly tuned in, but that is all. A.: We presume you have read our remarks concerning short-wave tuning, and you will find further remarks appearing in next week’s issue. Further than that we would suggest that you increase the "B" voltage. The set has been successfully constructed by quite a few and has been found to work excellently. The laboratory model gave no suggestion of any trouble. } I-TEN-SHUN (Carterton): The volume is often cut down on my speaker, but a sharp knock on the back of the unit sometimes temporarily restores it, A.: Your best plan would be to take the speaker to a dealer and have it repaired. 2. What is the life of a "C" battery? Would two such batteries aid reception? A,: Some "OC" batteries last as long as 18 months or two years. The number of such batteries must be determined by the voltage applied to the plate of the last valve and on the characteristics of the last valve itself. These you can obtain from the carton which accompanied or if you do not have this and mention the type of valve and your "B" voltage we can tell you the bias. " 8. Would an earth taken through the floor to a cold water pipe which enters ' the earth some 12 yards away be as

efficient as an earth wire of several feet long connected to a pipe driven in the ground? A.: The whole point hinges upon the word "several." If it is a long several it would be little better than ‘the eold water pipe. If only five or six feet

away it will be much better. The principle in installing an earth is to keep the wires as short as possible. 4. Does the Jength of the aerial given in the "Radio Record" of November 21 include the lead-in?-Yes, C R.G. (Auckland): Your cireuit is * very ambitious and would be little better than the ordinary circuit. You would have a great deal of trouble with it, and we do not advise you to go about constructing it. If you want coils designed for it we would have to charge a specialist’s fee of £2/2/-.