QUESTIONS AND ANSWERS

Radio Record, 31 July 1936, Page 48

QUESTIONS AND ANSWERS

a" Y.Z." (Hastings): Without the size * of the present wire and also the inside and outside diameters of the coil, together with its length, we cannot estimate closely the required quantities, If you supply these we can then calculate the sizes you ask for. " W.T." (Papanui): The two values * of capacity do not matter very much, as with the 0.00014 condenser the coverage of each coil would be slightly greater; but the difference is due to the fact that the 0.00014 mfd. condenser is more readily obtainable in two-gang assembly. As if a two-gang 0.00025 be cut down to the region of 0.0001, then the true value will be just under 0.0001, or else over and about 0.00014 per section It depends on the actual capacity per pair of plates in the particular make that is obtained, just how near to 0.0001 a cutdown will come. sé A:iW." (Nelson): The question of * twin ory single speaker is still a moot point, as there have been single speakers designed for the ordinary market that have shown up better than some twin units. ‘A good ten-inch speaker is very good, while a twin unit that has been designed as a unit. not merely two speakers mounted in the set, is also very good. An eight-inch twin unit would be better than an eight-inch single, for instance, but might not be any better than a ten-inch single. Hence it is necessary to compare the frequency response curves of the various available combinations and choose that which gives the greater flat top range. A.: In a well-designed set the inclusion of a shortwave band would not have

b- 4 mt any effect on the broadcast band at all. A,: The sum that you suggest would be just about right unless of course you wish a very elaborate cabinet, ete. These three questions are answered with re‘gard to the three requirements you have in mind in each case, ‘S C.B." (Darfield): The type of con- * verter that you wish is described fully in the "1986 Radio Constructor’s Guide," and all the parts are obtainable in New Zealand, as will be seen from the advertisements in that issue. Copies can be obtained from any stationer. or direct from National Magazines, . Ltd., Box 1680, Wellington, for 2/9 posted. "SR%" (Nelson): The values you give should require that the primary. coil be 40 turns, the secondary coil 16 turns, and the reaction coil 48 turns. The ‘reaction turns may have to be altered as they depend upon the valve used, ete. When the set is ready try the reaction at the low frequency end of the band and remove turns if necessary until the reaction control is smooth. "ELECTRIC" (Auckland): No. the B ’ supply cannot be.taken from the mains direct even if the mains supply is direct current. The mains supplying . alternating current necessitate the use of ° a rectifier and smoothing system, while the direct current mains will need at least a smoothing system. The running of the heaters from a battery is quite in order, but could be improved in economy if 6volt heaters were used. The current drain of the set from B batteries as shown is small, so that dry batteries last a long time, If you give more detail we could probably advise you better. "PYRO" (Feilding): The best thing to do would be to write to either the agents or direct to the manufacturers who will give you details how to overcome the trouble you are having. The coils are well designed in the first place, and it would be very difficult to do better yourself. Tel] them all the details, and it may be that you have a defective set of coils which they would then replace. A: The cans are specially made that size for use with the concentrated windings, and would not be suitable for high gain cylindrical coils. A.: The capacity of the condenser, per section, from the details given is approximately 0.0005 mfd.