Radio Broadcast - 1927, May - 61 Pages, 4.9 MB ... - VacuumTubeEra

RADIO BROADCAST ADVERTISER 59where R = 1000 ohms and w = 10, in the aboveformula, we have Iequal to the square root of10 + looo. Taking the square root, we obtain thesafe carrying capacity in current as o.i amperes,or 100 milliamperes.The resistances of various units as measuredin the Laboratory by means of the Wheatstonebridge were found to differ by about 3 per cent,from the rated value, which is close enough forall ordinary purposes. Resistors of this type aremade by Amsco Products, Incorporated, NewYork City; Ward-Leonard Electric Company,Mount Vernon, New York; the Tobe-DeutschmannCompany (Veritas), Cambridge, Massachusetts;Arther H. Lynch, Inc., New York, andthe C. E. Mountford Company (Kroblak), NewYork City.SHIELDSA RGUMENTS still continue among engineers,f\ experimenters, and home-constructors, re-'garding the shielding of radio broadcast receivers.Some say that coils, condensers, etc., if properlydesigned and properly spaced in the receiver, willneed no shielding, while others claim that shieldingis an absolute necessity.Until quite recently the home-constructor washampered in the use of shielding, because he hadno tools for working the material; besides, thelatter was hard to get. Several types of aluminumbox shields can now be had, and they may easilybe incorporated in almost any receiver requiringa shield. These shields usually come in knock-RADIO BROADCAST PhotographINDIVIDUAL STAGE SHIELDSdown form, and may easily be assembled bymeans of ingeniously designed corner strips.Their size is sufficient to allow a tube, radiofrequencytransformer, and variable condenserto be mounted within them without coming tooclose to the sides. If the size is not exactly rightthey may be cut down before assembly, as theyare in flat pieces. An accompanying photographshows one of these shield boxes, made by theAluminum Company of America, both inknocked-down and assembled form. The AluminumCompany's box is 12 gauge, 6 inches high, 5inches wide, and 9 inches deep, and is sold for$3.00. The Hammarlund Manufacturing Company'sbox shield is 22 gauge, 5^ inches high, 6inches wide, and 9 inches deep, and sells for $2.00.The Silver-Marshall Company makes a shield ofthis type which, however, is not knocked down.The box is 21 gauge, 5 inches high, 3 J incheswide, and yj inches deep. The price is $2.00.SOCKET-POWER UNITSTHE Balkite socket-power B units are all ofthe electrolytic type, having eight cells inseries which rectify the a.c. current from the line.THE BALKITERADIO BROADCAST Photograph"Kx" UNITThese cells are of the acid type having one electrodeof lead and the other of a special material.As a rule, this type of rectifier, combined withthe proper transformers, chokes, and condensersgives very quiet operation, and the only attentionrequired is the addition of pure water at intervalsof several months to take care of the evaporationwhich naturally takes place.In the instructions accompanying the apparatus,it is stated that the formation of a brown orwhite sludge in the bottom of the cell is a normalcondition and no attention should be paid to it.The solution sometimes turns pink, and this alsomay be regarded as natural. It should never benecessary to replace the electrolyte except incase of accident when the solution is spilled. Anew solution should be obtained from the manufactureror from the dealer who sold the unit. Ifthe electrolyte gets spilled in the metal case, thewhole unit should be shipped back to the factoryimmediately for a thorough cleaning, otherwisethe acid may cause considerable damage to theelectrical mechanism in the device and cause itto cease functioning.Sometimes when the electrolytic type of rectifieris left for some time without being operated,a thin film of sulphate will form on the surface ofthe electrodes which will materially lower theoutput voltage. There are two methods of bringingthe unit back to normal. For ordinary cases,the unit should be disconnected from the receiverand a short circuiting wire connected across theoutput terminals marked "High" and "Negative."The line current is then turned on for half anhour, after which the jumper wire is disconnectedand the unit is again hooked up to the receiver,and normal operation should be obtained.Another method which may be used is to put ajumper across the output as before and then shortout half of the rectifier cells at a time for a periodof about thirty seconds. In the Laboratory thebreaking down of the sulphate film was tried out,the voltage, in one case, being raised from 125 to140 volts. On one of the smaller units, the voltagewas raised from 105 to 120 volts. Both units hadbeen standing for some time. One model, the typeKX, which includes a trickle charger in the samecase, is shown in the accompanying photographon this page.A table of the price list and capacities is appendedat the bottom of this page. All ofthese Balkite units are for use with 1 10 to120 volts a.c. Models are sold for either 50 or 60cycles. They are manufactured by FansteelProducts, Incorporated, of North Chicago,Illinois.