Show 21 I 1 IL L li lz LL 4 cl L F 0 G 4 fig fla wiring diagram of tho the two tuba reflex set notes note the 22 post la Is at the top of tho the diagram by n C HITCHCOCK with this two tube set stations miles away y can be heard consistently on ID the its loud speaker selectivity la is particularly good and the be two main controls make the obern tion as simple as Is 13 consistent with goo floe tuning A panel about 1 7 by 24 inches would be suitable and if a cabinet la is wanted it roily may be 7 or more inches deep the circuit Is a reflex with a few unusual features the first tube acts is go a radio millo frequency amplifier the ille second as a regenerative detector and the detector output to Is fed back through the first tube which then nets acts ason as en audio frequency amplifier with abes two tubes stations eta tlona are heard clearly on the loud speaker with sufficient volume for all but the largest rooms A third tube with its audio transformer may easily be added if one desires to operate it loud speaker at its maximum power on distant stations the first tube will do most of the work as it acts as a powerful poi erful audio frequency amplifier and also as a radio amplifier Ilo however wever this does not overload the tube I 1 as the frequency energy Is small in view of the fact that this tube Is working at its limit of capacity it la Is necessary to give it the very best possible colida conditions for this reason a B D battery of the correct value Is absolutely essential A 00 90 vot volt B battery and a 4 volt tolt 0 battery will prove suitable for a tube and it if a volt B battery Is used a 0 volt 0 battery will be the proper size regenerative detector A regenerative detector la Is generelly conceded to be one of the most economical detectors and it has in this set let the added advantage of coming after a radio frequency amplifying tub tube e so BO local radiation la Is prevented tills Is a great advantage when several sets ire are close together A small email coll coil in the fig I showing form for winding basket weave coll coils plate blatt circuit serves to feed back bach effary wiry 11 into the grid circuit for regeneration era tion the placing of the instruments is not critical A type tube wig was used for a detector and if a dlf dif went type la Is used the value of the condenser shunted across the primary of 01 tte the audio transformer may need to be a slightly different value sockets of insulating material proved much icci more satisfactory than those constructed of metal general wiring hints ants are the be same as for any other hart set t keep grid and plate wires as on and as a far apart from each other 88 possible and it if they must cross let 1 it be at right angles all joints should quid be soldered with resin as f lux the low loss colls coils were homemade and a eave cave splendid results the windi wm form should have 11 spikes put lh routh holes hole s drilled evenly spaced aroulia ala mla a 3 inch circle in a wooden be v ysee ee fig 1 the wire should db ul yen around these spikes and w h ell 1 the t required number of turns la be n b een n wound the coll oil should then tied linly with string a nud ila slipped clipped oft off tile the K thre there will be no no difficulty in haslag kuig these colls coils f support supper t themselves atiat a tiff enough ough wire Is used those 14 I 1 1 hown are ct cl no 20 DOC wire the wiring diagram Is is shown blown in fig fie r for this set two condensers cl C l 1 u a 02 0 2 or L a mad capacity were 12 2 ind the colls coils to go with t them hem ih he ud la 14 have fifty ly turns turn s each e 6 other coils il 11 I l and M 13 3 are alf ali en turns roa each ach ickle eckl the rotor for tho to 0 be bj of the detector teeter does not need of 1 ow loss construction or have i 1 y a fery lot in low v distributed 1 l ia trl buted capacity as an it 11 critical radio frequency clr cir ulta A 2 0 rort inch composition tube with orty v ml ill ho be or fifty 7 tu turns ans of no 28 wire aoge ose the en rely ely suitable stable for this pur manner of fastening the tibe tn to I 1 to rod Is shown in fig 8 oleo aeu immell condensers were used and their values are given gen in the wiring diagram pig fig 2 testing set to test this set it may prove advisable to try it first as a regular tw two tube set that tant la Is its as a detector and one step audio amplifier without using the radio amplifier the internal wiring la Is exactly the same as ag fig 2 the only change Is to connect the antenna wire to io the left side of the grid condenser thus making a single circuit tuner with one control that of the variable condenser C 2 with this connection the first condenser 01 0 1 has no effect on tile the tuning of the set and the idea Is simply to familiarize famili arise with the tuning of the detector tube circuit auit and the working of the tickler with this connection it Is probable only the longer wave stations will bo be heard beard as the wave length of the antenna Is added to that of the set bet with this athla arrangement the output of the detector Is that Is put back through the other tube so that it acts as nn an audio amplifier though not acting as a radio amplifier at this 01 fla fig 3 showing construction details detail of tickler coll coil mounting time by tuning the dial of the con denser 02 0 2 stations should bo be heard it may be better to use a headset for this part pait of the test as only when the first tube Is doing its double duty does doea the set give power enough for tile the loud speaker fc if stations ore are heard connect the set as the lie wiring diagram shows bious with the antenna wire on the first fifteen turn coll coil this makes make a two circuit set out of the first tube one of the circuits being tuned with 01 0 1 and a three circuit tuner out of the second tube two of the circuits being tuned one with the condenser 02 0 2 and the other with the tickler if you do not hear stations clearly with the antenna on the second tubes coll try turning the tickler around as it may be connected up wrong simply rotate the tube degrees this will bring the tickler in the proper relation to the grid coll coil it if it was wrong at first tuning with the antenna connection in place on the first coll coil turn bark back condensers together to tune for a station it la Is best to turn tum the condenser 01 0 1 at the left slowly anu to sweep the second oae back and forth until the familiar chirp of the carrier wave Is heard then tune in the station by reducing tile the feedback of the tickler at ill all times the tickler should be turned so it has the smallest possible influence on the rest of the set for short wave lengths it will be noticed that the best position of tickler Is at nearly right angles to the grid coll coil and for the longer wave lengths it Is host best when about parallel with the turns of the grid coll new york herald tribune |