Questions and Answers

Radio Record, Volume II, Issue 21, 7 December 1928, Page 11

Questions and Answers

EADERS are invited to submit to "Observer"? questions that can be answered in this column. The questions should be short and concise and capable of a reasonably short answer.

feeling or attempting to identify the Wires by an insufficient light. You may have a little more light than you require thrown on the subject. It is when a lead. is taken any con‘giderable distance from the set that a difficulty arises. Some flex is bi-colour. ed, and this presents.no difficulty, but with ordinary light flex there is. ‘Mo determine *‘which from t’other" of these wires there are several methods, some @ little more efficient than others. . One radio enthusiast, or should we "amateur," for one does not feel inclined to say whom, was compelled, while experimenting, to have the B battery some few feet from ‘the receiver. Flex. was used to make the connection, and one end was duly joined to the battery. Half an hour later the other end was connected: to the set The: method of determining which was which of the wires won't be described It is not wise to suggest the wrong way. A simple way, having: connected two strands at one end on to the battery, is ‘to dip those at-:the other end in a glass-of. salt‘solution (salt and water). Bubbles will rise from both wires, but more from the negative. . This method should be employed whenever the wires are not separately coloured... In making speaker extensions, a battery could be temporarily attached to the set end to determine the wires. A Story with a Sting. THE same radio enthusiast tells another story — of..a method of increasing volume, which failed. A crystal amplified by one valve (double grid).. was not working too. well, and it was considered desirable to increase the voltage, and two 224-velt; blocks were. used on the plate and auxiliary grid instead of the customary one. Signals. increased but little. Desiring to experiment further, the amateur went about comparing two ‘speakers. One was fitted with a plug. Instead of. removing the plug and .using the terminals, this novice twisted pieces of wire round the end and round the body of -the plug, and with one speaker already connected: set about experimenting, Unfortunately, something slipped, a bright: flash----!

Another of these relatively expensive valves were purchased, and the job of fitting it commenced upon. Unfortunately, the -valve in question has a fiveprong base, for which holders are not obtainable in this. country, or, at the least, are very difficult to obtain, though quite easy to make. Everything promised well till it came to fitting the valve, of which the improvised base had not been secured. A slip, and away went the valve to the floor. . "All ‘good for trade,’ remarked the dealer. Now a cardboard safe has been made, and until everything is ready the valve has to wait, One of the old ones is used for fitting, and .each wire doublechecked, Above all, experiments are carefully conducted. A proper base has. qoeen made.

Concerning the B.D. ‘T AM building a four-valve B.D. but.am at a loss to know how many turns primary and tickler coils ‘require, I am using a V. 199 Radiotron valve for RF. amp. and a Philips 415 detector. How many turns would ‘you suggest ?-S. G.H. (Christchurch. ) The primary of the R.F. transformer requires 25 turns of 30 wire when a U 199 is used as the H.F. valve. 16 turns of 30 wire is recommended for the tickler but this should be added to or substracted from till the best results.are obtained. To Improve Reception. FIAviIne purchased a factory made machine, I am not securing satisfactory results. My aerial which is approximatel} 30 feet high runs due east and' west. The earth wire is fastened to a water pipe running into the house and is not buried I propose to alter my aerial, making 1. between 50 and 60 feet -high, and running in a south-westerly direction, and also sink a five gallon « "m inte the ground to the depth of three feet, filling it With water, and securing the earth wire to same. -Do you think this will result in better receptions?-J.F.W. (Pelorus Sounds). The italics are ours and would seem to indicate the cause of the unsatisfactory reception although rumour has it that the sounds are notori-

ously bad for reception. A ground which is not grounded! sounds Irish. Yes, J.F.W., we believe you have located your trouble and are going the right way to get results. You have a good machine and should get good results. English Sets. N the "N.Z. Radio Record" of the 16th instant there is an articie dealing with the radio exhibition held at Olympia in September last. ‘The reading of this article prompts me to seek information on the following points :-- 1. Whether, generally speaking, Einglish radio sets are suited to New Zealand conditions. 2. The name of any good English radio periodical.-Reader (North Auckland). A. 1. With slight adaptation of rails, English radio sets are suitable. The provision for high wave-lengths such as used by Daventry is unnecessary here. 2. The constructor and more or less technical man will find "Popular Wireless" (weekly), "Modern Wireless" (monthly), and the "Wire less World’ very useful publications, Life of the Valve. **(jOULD you tell me how long my valves should last?" That depends-tinker round with a screw-driver, and they won’t last long. Burn the filaments too brightly, and SPITE PL AROS ED IE EPA EAE OS EE ETE PAE TE TE TE LI LED

the useful life will be lessened considerably. If reasonable care is taken of valves, 2 minimum of 3000 hours may be assured, That is with a good make of dull emitter. Using the valves long hours, providing the rheostat is turned well down, will not shorten life in respect to hours, though certainly with respect to days. Some valves have functioned well for over 7000 hours, while one correspondent reports, he has been using his valves for five years, though they must have, by now, passed the point of maximum efficiency. Fitting a Low Voltage Valve. "AWN advertisement says that a fourvolt valve of a new type can be used in any circuit without alteration. You say that a four-volt valve if used with six volt valves must be protected with a resistance; I don’t understand." (THE advertisement was right, and so was the writer. That particular valve is intended for a four-volt battery. In that case 10 adjustment is necessary to fit the valve to the ordinary circuit. In the case of a six-volt set it is necessary to protect the fourvolt valve by a rheostat (variable resistance) of not less than 30 ohms, These are fitted in the wire going from the terminal on the socket marked ++ by lifting the wire from the holder, joining one leg of the rheostat to this terminal and the other leg to the wire removed from the socket. Such a rheostat is inexpensive, and the little trouble taken in fitting it is well worth while, as the rheostat should be kept fully turned on. WING to pressure on space a few replies have had to be held over till next week. ‘There are still a few replies to be seat by post.