A B and C Battery Etiminators

Radio Record, Volume III, Issue 10, 20 September 1929, Page 39

A B and C Battery Etiminators

. 7 Electrification by Easiest Method

OR the set owner. who does not de_sire to rebuild his. set, the. construction. or purchasing an A.B. C. eliminator ‘will probably appeal: This type of eliminator is quite an effective * Way of. changing over to the A.C, mains for currént. "A" eliminators. have for some time had very matiy drawhacks,. but they have been mow brought very. near to perfection, and good ‘results can accrue. by, their use. ‘The eliminator consists

-of the following parts, -A transformer ‘that’ will step doivn from the A.C. mains t6 10 volts supplying ‘about 3 amps. ‘of. current; .an electrolytic condenser or other. big capacity smoothing. condenser ; an audio frequency choke wound with wire: sufficiently heavy to supply enough current for the set, and a ‘rectifier which .will likewise pass enough. current: This~ latter may be of the metallic type, electrolytic or valve. The. electrolytic rectifier al‘though economical in, its first cost, is otherwise unsatisfactory. The dry -ree‘tifiers. have had. ‘great popularity reeeritly, dnd are. proving themselves very. efficient. They. are slightly dearer in the first cost,. but are well worth in talling. Valve. rectification still remnfiins very .popular,: although .after a _certain . period of use the filaments burn out.

By reference to'the diagram, it will be seen that the "A" battery eliminator is very similar to the "B" eliminator, but is constructed with very much heavier wire. .Ly- efficient smoothing, very little hum will.resylt, If. it is. required to fucther break down the current, resistances which will pass sufficient current must be put in series with the positive lead. The diagram shows a method of bringing this about by using the ordinary 30 ohm yariable rheostats.

"B" elimiiators are veadily procur‘able and very easily made, although their manufacture requires a little care and, plenty of patience. . Their construction has been fully described in the "Radio Listeners. Guide," and this has been supplemented by further articles in the "Radio ‘Record." Grid bias may be obtuined ‘by a resistance at the end of the "B" supply, or by a separate bias unit... Such a unit was described in our issue of July 12, 1929 (Vol. IIL, No. 1). A workable "A" eliminator may be constructed by "shunting the output terminal of a battery charger with an electrolytic condenser. and connecting the positive lead with a choke such as has been described. This reduces the voltage, and unless tapping is higher than 6 yolts is provided, 4 volt. valves only can be used. :