Show I 1 five tubo tuned radio frequency diagram using square wound colls and straight line frequency condensers by CARLTON CARL TON E BUTLER member institute ot electro eal engineers and institute of radio t engineers changing conditions make new radio circuits necessary A few years ago the single circuit and ultra f hudlon receivers were satisfactory nd were capable of bringing in als s tant stations with volume today the A same sets cannot be used except in isolated districts away from broad casting stations due to their broad tuning qualities f the receiver of the earlier day Is A tj no longer satisfactory for other rea bons principally on account of its squealing and radiating qualities and because its tone quality Is poor and distorted at the last radio confer ence in washington it was agreed that in the near future the use of radiating receivers would have to be ended e en it it became necessary to pass a fed oral law to accomplish that result today with modern laboratory standard apparatus available and with seta of better design the quality 0 attains the standard demanded by t lovers of music the jl 4 circuit as developed for f use in a new receiving set Is a good example of day design the most popular form of circuit was selected the fie tube tuned radio 5 frequency and by the use of the lat v est type of condensers colls and transformers together with improve y in the circuit produced a receiver that Is capable of tuning through interference bringing in sta a distance on the loud speaker and surpassing many re calvers tor all around performance and quality of tone 1 to shut out stray currents of the improvements in the circuit are two by pass fixed con den sers between the primary of each of the first two radio trans a formers and the filament this serves i to bypass and 1 beep stray radio frequency currents out of the rest of the wiring and stabilizes the circuit A large condenser is placed across the C battery terminals to reduce noises t and howls due to long leads or low ft voltage refinements in apparatus include the new square wound horold coll with shenew line frequency condensers which provide shielding of electromagnetic lines of force as rell ni keep the instrument a mighty important detail the colls eliminate the spraying effect of magnetic lines of force the set proper and re move the principal bugbear that radio engineers hae been working for aars to solve the colls have self pon i fields that make pickup of stray y current impossible their use in the n 4 receiver makes a set that will tune through strong interference ejk alche variable condensers on the first v and second stages 1 of radio may be tuned by one control aa in the fractured receiver if desired three 1 condensers and three dials may be an fn the ordinary manner how ever without r the parts needed to construct the circuit you will need the following fa 71 7 1 square wound horold coll type tl indicated on diagram as LI 2 square wound horold colls type ta indicated aa 12 and 13 3 straight line frequency condensers preferably the all amerl can shielded type indicated on diagram as cl ca and ca f 2 bauland brie audio transform ers type 3 fated condensers in on diagram as ca ca and ca 1 mad fixed condenser in on diagram as CO 1 10 mad fixed condenser tn on diagram as ca vy the rheostats should each be of ant six ohms capacity for the use of 7 A or 0 A hubei and the grid f ff leak ra should be two when f using the new UX amplifier tubes y break the grid return of the last transformer and insert C battery of voltage recommended by the manu fac the first rheostat Is used as a f volume control to moderate signal strength to the desired extent for f most satisfactory operation the correct setting of this control may be determined by trial and then allowed to remain without further adjustment in addition to the apparatus named above you will need five sockets a 7 by 24 inch panel baseboard or wire screws colder etc to complete the set the terminals of the fre quency transformers are unmarked in the diagram the first coll la a coupler with two taps taken off tor long and short aerials both taps are marked A and each should be tried and the aerial connected to the one that gives the best results the other two taps are the secondary connections and in the regular way the outside terminals or the second and third colls are the primary posts the inside terminals being the G and F secondary terminals three circuit Is best short wave radio set an easy short wave set to build Is one on the order of the three circuit set the tuner for this set Is made from any good three circuit tuner about 4 inches in diameter the secondary consists of ten turns of no 12 D C 0 wire the primary of four turns of the same size wire the two being medium coupled the tickler has 20 turn of no wire the secondary Is tuned with a mad condenser as shown by the diagram showing circuit of the short wave set sketch another important point to note Is in winding the tickler to obtain the best results care should be taken to ee that all turns are wound in the same direction and an even number of turns on each side of the shaft this set will receive approximately from 2 to 10 kilocycles kilo cycles or from 40 to meters however aery set Is different and in order to check your maximum and minimum wavelengths you should obtain information from the standard frequency station as to when they send test programs and with these signals you will be able to tell exactly what wavelength wave length our set will cover in assembling a short wave receiver keep in mind the fact that all leads should be just as short as you can mate them if you can get the advice or assistance pt one of the many ama deurs who leavo successfully built a short re celer it will be of great assistance philadelphia record straight line tuning making bid for favor the coming of the straight line fre quency condenser jand the later arrival of the S L r dial converter has brought the subject of straight line tuning very much to alie fore the between jhc thc two instruments rests with tan when he de to simplify the tuning of his receiving set A straight line frequency condenser of tart plate type will solve the problem of obtaining simplicity in tuning by an electrical method and it Is conceded that the best way of solving an electrical difficulty Is by an electrical change the S L r dial will afford one dial visibility and greatly simplify the tuning of short wave stations and wherein a change of condensers would entail too much work may be used it must be remembered however that the S L y converter ahl Is a mechanical ch device and therefore will not entirely solve an electrical problem to avoid body capacity A good general rule where the object Is to avoid body capacity la to always make that terminal of the instrument ment to which your hand comes the closest when tuning at or near ground potential As most circuits are tuned by a variable condenser across a coll the rotor plates should be the end connected to ohp filament circuit the hand in effect cornea closest to these plates since the rotor plates connect to the shaft aal tha shaft carries the dial cut down distortion cut down distortion by hooking variable grid leak across the second ary 0 the second audelo transformer |