A FULL-WAVE B BATTERY ELIMINATOR FOR HOME CONSTRUCTION

Radio Record, Volume I, Issue 16, 4 November 1927, Page 14

A FULL-WAVE B BATTERY ELIMINATOR FOR HOME CONSTRUCTION

A CONSTANT AND PLENTIFUL SUPPLY OF HIGH TENSION AT LOW RUNNING COST

(fourth Instalment.) A plan of the eliminator with cover removed is given to show the position of ‘parts. A radio choke is connected directly in series with the plate of each rectifying valve, and one of these chokes is conveniently attached to the partition alongside the valve by a screw through the centre. The other radio choke may be fastened to the baseboard in the position shown, these chokes heing marked R.C, in the diagram. The bank of condensers is best placed in about the position shown, but the HT choke may be placed in any position. A good flan is to stand it on end against the partition and attach it to the latter by means of a small brass angle-piece or other means. THE RADIO CHOKES. The two radio-frequency chokes are constructed by cutting four circles of cardboard 2hin. in diameter. The centres are made from the shank of an old wire 12" 5

Spool by sawiny through and sawing off two circles 8-l6in thick. Tach of these circles is glued to the centre of one of the cardboard discs, and another disc glued on the other side to form a spool with a 38-l6in. slot to take the wire. A hole is made near the centre, and the end of the 34’s enamel wire passed out, and 1000 turns are put on, the end of the winding being passed out through another hole. One end of each choke connects to a plate of each valve, and the other ends to HT1 and HT2 respectively on the transformer, through the FIT fuses on top. THE FRONT PANEL. This ebonite panel measures 6} by 7% inches Upon it are placed the three voltage output resistances, the rheostat, and the fuses. The three variable resistatices are ‘‘Royalty’ type B, 1500 to

100,000 ohms, 8s. each. In addition to these-one or two- fixed carborundum resistors should be included in the detector circuit. If it is desired to get down to about 30 volts, a fixed resistor of 100,000 and another of 50,000 ohms should be included as shown, by soldering the end tags together and connecting the pair between fhe arm of variable resistance, and the wire leading from condensers 1 and 2 and connecting to the arm of each variable resistance. The other side of each variable is connected to the bolt above its respective output fuse and terminal, and also to its respective fixed condenser indicated by the figures 8, 4, 5, below. The rheostat should be of the power type, capable of carrying 8 amps. One side is connected to one side of each valve filament, the other side to the lowest bolt on the distribution panel, , If this panel is dispensed with, this connection wilt be direct to one of the transformer taps most suited to the filament in use. In making such filament connections, it must be remembered that they must always be made to the Saine number of turns in each layer, as the action of the éliminator depends upon drawing the HIT current from the electrical centre of the filament winding in actual use, and in practice the electrical and mechanical centres are sufficiently near together, even if they do

not happen to coincide, su long as equal turns are used in each layer. Deviation from this rule would be liable to introduce huin, which it is the chief function of the eliminator to cut out. The negative HT terminal is connected to one side of all condensers, and also to the HIT centre tap of transformer. Next week the construction of the high-tension choke and the outer case will be dealt with. The writer is trying ont an idea that if successful will cut the consumption of a.c. down to about one-half. A report will be given next week on the matter. Constructors are advised meanwhile not to purchase valves. The correct circuit diagram is included in this instalment.