Show eliminator Is very useful part device serves to harness usual electric light ing current B CHARLES GOLENPAUL there la nothing really complicated about the usual B eliminator ii acnes to harness the usual electric lighting current obtained from the nearest socket or convenience outlet to the radio in place 0 H bitterley bit just how tills Is Is worth knowing by those now a B eliminator and by those the early pur chase of such a device to begin with the usual alternating current that comes from the socket or convenience outlet cannot be employed for radio purpose it Is cui rent thit flows first in one direction annl ahen in alie other changing its direction of flow nt the rate of many times per second such undecided cur rent if we may term it such could not be introduced in a radio circuit without causing haac so it Is obal ous that the alternating current must be straightened out or made to flow tn one direction only through transformer the first step Is to pass the niter dating current through a transformer which up the original voltage 0 telco or more its potential in order to operate the mechanism that fol lows the current Is still alternating in character despite passing gli the transformer the current from the transformer Is now led to a most ingenious device which we may call an electric turnstile it Is similar in action to the turnstiles turn stiles used in subways and electric railways for the purpose of let ting persons pass through in one direction but barring them if they try to pass through in the reverse direction such an electric turnstile Is called a rectifier in the usual B eliminator either the raytheon or recal fier Is employed the former Is a gaseous conductor tube without a filament to burn the initial current causes a certain breakdown or loalza alon of the gas which establishes a path for the one way conduction of the current in the case rt r t the a Is employed and the particles or electrons given oft bv the heated filament metal establish the one way bridge for the alternating current some B eliminators em ploy chemical cells which bae tha one way conduction property filter stops ripples most B eliminators are full wave rectifiers velch means that the en tire alternating current Is passed through by means of a double turn stile arrangement with one gate thrown open while the other Is closed and co versi for greatest efficiency alaf wave rectifiers present only one turnstile which Is thrown open only at every other internal when the alternating current Is flowing momentarily in the right direction now the current tint has through the electric turnstile or Is flowing in one direction because of the turnstile action it comes in pulses EO that it Is called pulsating direct current if applied to delicate rad 0 circuits these little pul or electric ripples would make their presence known by erces alve hum so the current pissed through a filter to iron out the ripples the niter consists of two elements chol e colls and filter coddens ars the choke colls serve to check the pulsating current while the flyer condensers serve to store alie current A beautiful electrical balance Is struck between choked and condensers it Is ns though we were employing a dam to control alio spring freshets fresh ets widen would otherwise pour down n villey as uncontrollable floods the chokes ore the dam v title the con beners fire the impounding area or behind the dam As n result of the damming action the fre are into a steady fow of water throughout the year for alon and other useful purposes just ns alie pulsating current from alie B eliminator filter Is converted into a steady flow of current quite free from hum the register bank now alie current issuing from the filter circuit would be ready for use if just the full output voltage were however it Is seldom that a radio receder can employ the full output nt all times generally here are marious kinds of tubes requiring dlf crent voltages furthermore n berntn minimum load must bo main across mot filter circuits and tubs to insure proper and bafs operation hence the filter output Is now delivered to a so called re el stance which in terms of analogy is like a gatehouse git ehouse of n water supply ss tern la that it distributes the flow of current over different changela ch annela two stations for india before the end of the sear two largo broadcasting stations in bombay and calcutta will bo in operation by the licensed indian broad a report to alie do partia ent 0 commerce states shields and ono R F stage in F J how copper shielding orrl in selectivity as the sensa 1 radio set Is increased las t i r robert r gowen ol the ff radio in a korv te 1 netly shielding prepared orrt per and brass research as 1 pointing out that the J a set gets worse aa the ot canies conies higher mr gowen es adding stages of frenden to provide lla broadens out the when the signals are deliver ji 1 tube there are with them signals from othe gt operating on nearly the baiao T quincy this loss in selectivity result the act that radio frequency added are damped or nent iced in order to present oscillation a to inner stage feed back of f from the coupling between thel duc used many schemes are used to bre tills feed back without excer damping and according to the when more than two stages ot balte frequency are employed the probie becomes more difficult it becony necessary to use magnetic sh leldia to prevent coupling between the la duc of tire set and to the loss in selectivity as the swa Is increased experiments show that inter stag shielding Is not enough and gowen declares that the day Is not far distant when all receivers wu i ta completely shielded cop per cases otherwise it will not 1 possible with broadcast stations work ing on superpower for a set in a can transmitting area to be affect ed by the desired station alone stromberg carlson Is cited as oa manufacturer who has enough to make it worth while ant lias used sheet copper for shielding indications are that battery leahi must be shielded eventually also engineers and manufacturers in now beginning to see that the trad toward the ideal set of the future b to reverse the present practice of building receivers of i great number of tubes as these r calvers require an amount of power supply and maintenance elaborate shielding to prevent abter stage oscillation in the art frt quency stages the new line of development Is to build a simple cr embodying not more than one ra dlo frequency stage of highest efel clency and selectivity in a shielded copper cabinet the highly efficient browning brahe and alim merlund roberts sets are good present day examples of this design it safe to rs sume that eventually shielded cabinet will Include he y er unit or batteries until power unto are fully developed so that there w be no chance of pickup from cobl employed tor connection plug in mounting for the Short Wave boik A very convenient and fiet of mountings tor short can be made from a few U teb bt es a UX socket and a few strip of the tube bases are cut off as illustrated and soldering ings are soldews to the tops of the prongs then a hole Is drilled in the center of the tube base and it Is bolted colht bakelite strip care must be taken that the head of the screw does cot how to mount plug in coll in alc aum tuba socket j project above the surface of the strip so that it will not come in cona 1 with the coll i ihloff strip Is drilled at the endi the coll Is bolted to it by another aai awi of tho same length y the socket Is mounted on one of a wider strip and the the other i the mounting tor the arl made out of a piece of U 63 alte supported by a braclet ft bl made from a piece of sheet brass a piece of brai tubing te P bolted to it by another strip 01 piece ct bakelite M two pieces of heavy copper ta are fastened into holes piece of bakelite are w terminals for the primary if a bubp mel s used W s and the primicy may be tt erectly oil tha should be tapped alo if orlue a fixed costal as a p tor let it fit into a r oth than attaching it rest of the setup floii Sl order to enjoy the bt ad gt it win be necessary to tap wv to bring together new sit tills tapping Is done awe v tal hooked in the e rest of the set 1 v alons may le jarred loo y the crystal 1 1 i athla po |