QUESTIONS AND ANSWERS

Radio Record, Volume V, Issue 23, 18 December 1931, Page 36

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. 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.

"TJOREKH" (Hokianga): Will the "Super Six" work with the air-cell battery and R.C.A. valves without alteration? A.: Yes, but if you use a screen-grid R.C.A. valve you must note that the grid connection is at the top of the valve, and must make allowances for this when wiring your set. . . 2. Can a pick-up connection be ed in the wiring?

A.: Yes. Take out the 1 meg. gridleak between the grid of the detector valve and A-+, and place the pick-up connection in its place. If the quality leaves anything to be desired, take one end of the pick-up to the grid of the valve and the other to A- instead of the A+, as shown. 8. Will it work with the frame aerial

only, and are any alterations needed for work on short-wave? A. : It can be used on an outside aerial by using a coupling coil in the place of the frame aerial, but in doing this the P. and T.’s regulations would be contravened, for it would create interference. It will work on short-wave only if a special short-wave loop is employed. These may be purchased in commercial form at a very reasonable price. "PARKS" (Featherston): Could the \" potentiometer of a carborundum staunit be used for the "Night Owl Three"? A.: Yes, it can be used across the filament in order to provide the grid return. The pole marked negative will go to the negative wire of your set and the one marked positive to the positive one. The grid return will come in, we think, to connection No. 2. However, try it to No. 1 also, if No. 2 does not give satisfaction. 2, Would the set work without the aluminium shield? . . A.: Yes; you may have a culty, however, with hand capacity. Nevertheless, it is worth trying. " AVE-TRAP" (Dunedin): I have constructed the "Dual Wave-trap," but have not had any success, not being able to eliminate the local station. . A.: It would be as well to put-on rather more turns than specified, and tap them, as indicated, trying different combinations. Use the optional tap and the aerial and try to tune out the local station. Until you get your wave-trap working on this one it is useless to try to get it operating in a dual fashion. Then try the optional terminal and the one marked "set" in order to get the wave-trap operating on a "RB" class station. Having thus eliminated each station in turn to your satisfaction, you can use the trap as a dual wave-trap. . p*2t (Taranaki): In my commercial all-wave set, using plug-in coils, the top part of the band is nowhere near as sensitive as the lower part. If I had special coils made to cover each half of the band. would this state of affairs be remedied? A + Tn all probability. ves. All-wave

sets often compromise on the broadcast band, and quite likely this is the cause of your getting unsatisfactory results. We should advise you to write to the New Zealand agent, who may be able to help you further. "TP 2SPERATE" (Matamata): Must a bias resistance in an a.c. set be capable of passing the current consumed by the valyes? . A.: Yes; this is of paramount importance in designing the set. If your bias resistor will not pass the current, it becomes unduly heated, and the resistance rises. This means you are putting a higher grid bias on your valve than that recommended by the manufacturers, and consequently are getting distortion. 2. Is nichrome wire suitable for bia: resistance ?-Yes. .

3. What is the total yoltage to apply to a push-pull stage of 245’s allowing 250 ii for thé plate?-300. 4, What would be the current consumed by a pair of 245’s in push-pull with 250 volts on the plate? A.: 64 mamps. 5. At what temperature is nichrome resistance wire kept when making resistances A.: Usually about 80 deg. Fah. 6.: My "Radiogram Five" works fairly satisfactory, but weakly, for a while, and then distortion becomes very bad, and the set ceases to operate. A.: It seems as though your grid-bias resistance will not pass the current taken by the valves. This means that it is heating, and, as we have explained in answer to question No. 1, is causing a greater bias than that recommended by the manufacturers to be applied to your, valves. Bias resistances In an a.c. se are very critical. A RM. (Auckland) : See the description * of the "Picnic in this week’s issue, X43A (Whangarei): Could the "Super Six" be adapted for use with an outdoor aerial? A.: It ean be used with an outdoor aerial if a coupling coil is used, but in these circumstances it would contravene the regulations of the Post and Telegraph Department. An outdoor aerial, however, is not really necessary with the "Super Six," as it would bring in a very great amount of extra noise, and would probably defeat its own object. Nevertheless, it is possible we may design a coupling unit. We shall not make any promises. »2

Af P, (Hautapu): Why is -my set very * weak in the day-time? Even under ‘00d conditions, I can only get Australia and New Zealand. , A: In all probability your condensers need trimming up. This, however, is not a job for anyone who dogs not know his way about a modern electric set, so we would advise you to get a radio technician to look at it. ; "TT 'RIOKLD CHARGER" (Khandallah) : Who are the Wellington agents for the Leweos coils?-Fear and Co., Willis Street, Wellington. | . : _2. Would an amateur with a serviceman’s certificate be breaking the new regulations if he constructs his own mains apparatus, but has it passed as being satisfactory by a certified radio serviceman? A.: No, 8. Is the amateur constructor permitted to sit for the R.S. examination? A.: It is primarily for the radio salesman, but anyone is allowed to sit for it. "NTEVA" (Wellington): Would you ~* kindly give me the number of turns for the coils for. the "Radiogram Tive" suitable for a .0005 condenser? A.: For the secondary use about 10 turns. less than’ the numbers. specified, Reduce the primary by three turns, leave the tickler as it is at present. Use the gauges of wire specified in the article. A G. (Inglewood) : Which is the better, * the "Super Six" or the "A.O, Cathode Super’? ‘ A.: The a.c. "Cathode Super" is a much more ambitious set than the "Super Six." Nevertheless, the "Super Six" will give better results than any battery ‘set we have yet published. The a.c. "Cathode Super" will give you everything you want for dx purposes, and you can use it oft the aerial, wheréas you cannot do so with the "Super Six." You put up a fine piece of work in logging the Indian _ station using 60 watts. Congratulations. This is a splendid record, and we wish you luck in the dx competition. -*X22Nw (--~): How can 1 use au output filter with my set which employs a double jack in the Jast stage? The jack is used to break the filament circuit. A,: The diagram herewith shoyld show you how to‘go about making the cennections. 2. Would a 45-foot aerial passing over the corner of a house, 10ft. high, be more

effective than one 85 feet clear of. the ground? A,: There would be very little difference between both aerials, We think the one that passes over the roof would be the more effective, J ©. (Dunedin): I am' dismantling my * battery set to build the "Super Six." I have the following six-volt valves: A624, PM6D, PMDX, and PMG. If I purchase. anothér PM6D for second detector, and another A642 for the streen-grid stage, will they be correct? Will a PM5X do for oscillator? . A.: Yes, the combination will be quite in order, and PM5X will do for the oscillator. — 2.: The R.I. general purpose transformer, we think, would be the better one for® the circuit. ’ 3S. We regret we will not be giving cvil specifications for the set. Much of the secret of success with super-heterodynes lies in. the coils, and we think that when they are as complicated as are the "Super Six" coils it is not worth while publishing the specifications. "PADIO" (Wellington): What kind of wire would be suitable for stringing insulators together? A.: The wire you enclose should be quite suitable if you keep your insulators clean. However, if you let them cake with dirt and become conductors, then much electricity will be lost through the wire. However, it is unlikely that the insulators will become very dirty. 2. If the earth wire were soldered to a copper plate anfl then fastened to an earth pipe-with earth clamps, would one be robbing the other?-No. D*%74 (Auckland): I have a .0005 mfd. condenser having 25 plates. Tiow many must I remove to obtain the value of .00035? A.: The total number should be 19.