Listen in Theres Lots to Hear.

NZ Truth, Issue 1127, 7 July 1927, Page 2

Listen in Theres Lots to Hear.

"B" Battery Eliminators

1 ♦ Chokes 2Mtid High-power Transformer

\ (By "Crystal.") it is very essential when constructing a "B" eliminator, that the chokes and high power transformer are of the very best if flawless reproduction is required.

IT is not a scrap of use purchasing all sorts of makeshift devices to do the work of these two units. A niter choke must possess an inductance of a certain 'value and must not exceed a certain direct current resistance. Results' of a kind can be obtained with the secondaries of burnt out audio transformers, Ford coils etc., but they are of high resistance, and substantially reduce the amount of current available, A similar remark applies to the power transformers! ' They must be correctly designed, and with no shortage of wire on the primary winding. Great care should be exercised when constructing to see that all the windings are made m the same direction. These windings of the transformer should consist of 3 separate bobbins, each I inch wide, the centre one of which is the primary, and the two outer bobbins containing the two halves of the secondary winding. The forms for the bobbins should be made of stiff fibre 7 -Bth inches m Width, shaped on a former 1 1-lGth inches square. I For the power transformer required to • operate an eliminator for use m conjunction wiUi a "Raytheon" rectifier,tube, the following are the particulars. The primary should consist of 21 BO turns of number 30 D.S.C. wire, while the two halves of the secondaries should each contain 2500 turns of No. 34 D.P.C. wire. < When the bobbins have all been wound, m the same direction they should be, fastened with a piece of tape to hold them firm. They are then Immersed m a tin containing a mixture of half beeswax and half rosin, which has previously been melted and well stirred up The bobbins should be left m until aXI the air bubbles have ceased rising tm the mixture. They should then taken out and allowed to cool off, fer which they will be quite hard and firm, ana can be handled safely. The bobbins are then ready for connecting up. The secondary bobbins aro, placed one on each side of the primary^ , The 'primary leads are left/uncennected until placed m circuit, wh*n th«y are jotnad to the input terminals carrying the 230 volts A.C. ' Tho tra.nsr-r.rmer core is then built up jtr"jn 1 inch width strips of stalloy or silicon steel ef 28 guage, sufficient be'M^jgtfrchafee&jtc stanayLinches hlg+\,

of each size, which when built up will give aX-inch com ,^ . These wilt be required 4% in. x lim and ■2%ih. x lin., this will make the ;ii>side of the'cbre 3%ins. xl%iris. The method of building up, the core is done , by overlapping.; ; V. - ;' > ' ■The filter chokes > are wound 'in a similar manner to that of ; the transformer' windings. ...'■..; They consist of two separate bobbins' Z% m; lojag on a 1 l-16ih. square former, on each of" which is wound 6000 turns of No. D.S<C.(Wire.v .-■ ...... ; . ; ; , ,- ; These bobbins should bjel wound ! '" /the same direction «s already ■■ advised, the butpide turn of ! one bobbin is connected to the inside ; :turn :^jf the other. The centre/tap should be taken fromthis pointy Both : bobbins are mounted on the same .core, . one on one side of the frame, the other core 6n" the other side ..ofithe frame. -•■■'■■■ ;'- v^-' :: a ■■■■■■' - v . ■■■['.' - ; : v The;;core is; built up of 5 7-Biri. x lih strips and 7.-Bin. x lin., giving the in-: side measurement of :■; 37-81h^- x ; 7-Bin.; the method of' building here is quite straightfonvard. :•'•".■' '..'■: "'- :- a •. / The; two long strips; are laid parallel and then the 7-Bin. strips iplaced between' them, thus * forming ah oblong frame w^hcise outsifle' measurement will 5/7-BiUv long by 2 7-Bin: wide; ■-:'■' \^Vhen. this core. has been; completely assembled a thin card should; be/inserted at one of the joints so that a small air gap can b,e/ preserved. • ; :^hen the: whole; has been clamped together it should be immersed i?v ihe beeswax-r-i'osjh mixture m a similar manner to the ti-ansformer. ;: The piece of .card should be pulled but, after which the. -ch plies are conipleted>r:,; ■•■;■ '■','', .;. - i ': v ..;" ;: ' "■'■■• - ■ '■''.'■'■