Show 4 7 ca L FF 12 7 C C cz RZ 5 ond that la Is selective enough for use ue in wiring diagram of a three tube set metropolitan areas and which gives pine fine quality of signals by J E ANDERSON in radio world the three tube set shown in the diagram la Is a standliy standby stand liy by that brings in all the local stations station 9 with loud speaker volume of moderate intensity but wonderful quality utmost simplicity of operation consistent with satisfactory selectivity greatest purity of tono obtainable with standard parts anti and strictest economy of operation were the lie objects sought to obtain simplicity of operation a double condenser was used for the two tuned circuits for selectivity a low loss losa tuning coll coil was wag used in the radio frequency amplifier and tills stage was made regenerative A crystal detector and two high grade audio frequency transformers were se ee lecter for economy of operation dry cell tubes were employed winding the colls coils the colls coils LO ll LI T ore are the three winding of a standard three circuit tuner it may be any of a number of low loss colls coils on the market 12 and IA 18 constitute a homemade home made radio fre quency transformer the core la Is a 1 inch diameter birch dowel 1 inch long this la Is mado made into a spool by cementing two insulating washers 1 inches in diameter to the two ends the primary winding IZ 13 Is wound next to the core and it consists of 20 turns of no 80 double cotton covered wire this winding Is covered with several 1 layers yer of heavy wrapping paper then on top of tills this Is wound the secondary 12 consisting of 03 93 turns of tile the same kind of wire the secondary Is wound in two layers lasers since the wire used winds about 73 turns to the inch tile the two layers were separated from each other in tile the same manner as were the two windings A protective layer of mending tape wall put over the secondary the terminals of the two windings were brought out to small wood screws fastened in the ends of the wooden core and these were tinned for soldering connections the transformer 12 13 may be wound with heavier wire eor or it may even be a 11 low loss RF tuning unit in that case more room will bo be needed on the front cover coll coil adjustment it will be necessary to adjust the two colls coils so that the two tuned circuits ll LI and 12 are in resonance with the same wave at some setting betting of the double condenser this la Is best done by putting more turns on it 12 than I 1 feces necessary sary and then removing a turn at a time until a given signal Is loudest in the present set the final adjustment left 03 turns on 12 how panel la arranged at tile the lower left corner of the panel are the two binding posts for antenna and ground symmetrically placed in the right annd corner are the two jacks the single maln main control la Is in the center which actuates the rotor of the double condenser on the left of the main control Is the knob controlling the tickler and on the right of it Is the rheostat directly under tile the analil control Is we tue filament switch the panel la Is 7 by 18 indies inches the set was mounted in a cabinet 7 by 18 by lol inches A deep cabinet was selected so that all the batteries could be mounted back of the baseboard three no 0 6 dry cells cella and two upright 22 volt plate batteries are used and these are securely hold held to the back of the cabinet by two brass strips uses crystal detector the crystal employed Is the new type fixed detector this Is stable in operation and very sensitive as compared with the usual fixed crystal detectors however it if must bo be handled with reasonable reason able care or tile the sensitive point which rests against a burnished steel plate may become crushed which destroys the sensitivity the two audio frequency transformers used are federal 05 first AF and WA second AF these were selected because they have it ve very ry satisfactory is quality characteristic and will maintain the good quality delivered by the crystal there ore are two jacks jl for listening in on the first stage of audio and ja for the last stage tile the last should prefer preferably abl Y be a filament control jack which closes the circuit of the last tube when the plug Is inserted in it otherwise out a switch in the he IX FX lead of the last tube A single rheostat ith Is used to control tile the current in all the tubes tilts la Is used mainly to take up the excess ex cess A battery voltage when the cells are now dow over the discharge voltage volta gp A 0 to 10 ohm rheostat Is most of the excess filani filament ent battery voltage Is taken up in the resl it II each of these la Is of such magnitude that the voltage drop Is about 8 volt and this drop Is used its as the blas bins 0 on it the grids of tile the amplifiers these are r small mail colls coils of nic nl chrome hront wire Ampe rites of the proper type may be used in place of these resl stancey and in that case tile the single rheostat rh may be dispensed with or it may be inserted in hi series with tho the filament of the first tube only list of parts parts required for tile the construction of the set are one low loss three circuit tuning coll coil LO LI T one RV RP tuning coll coil la 13 12 one double condenser with vernier dial mad Nut national ionni two audio frequency transformers one fixed crystal cr one double circuit jack and ono one single circuit jack 01 jl ja three sockets three ballast or amper lies ites 11 II 11 one rheostat six to ten ohms ith one fila filament switch S six binding posts posta one small knob for tickler control one panel 7 by 18 inches and one on baseboard to match |