Simple Battery Receiver

Sun (Auckland), Volume III, Issue 855, 26 December 1929, Page 7

Simple Battery Receiver

HOW TO CONSTRUCT THE SUN THREI Fidelity Of Tone Its Big Feature RADIO BROADCASTING has now reached the stage when quality of reproduction-counts more than ability to reach distant stations. This is particularly so during the summer months, when longer •days and increased static effects make it almost impossible to secure pure reception from Australian stations. In the following article Mr C. R. Russell shows how to construct a simple battery-operated receiver, which, when used with a dynamic or other first-class speaker, will give fidelity of tone.

The Sun Three is a three-valve receiver employing the well-known RBD circuit, in which respect it is similar to previous receivers which have been described in these columns. Tile present circuit, however, has been slightly simplified, and provision has been made for a power tube thal will satisfactorily i —crate any movingcoil speaker now on the market.

Two strong terminals mounted on ebonite strip. One valve A4OH. One valve A 415. One valve 8403. One 4-volt storage l>atUi*Vw Three B batteries 45 -rolls each. Supply of bus ba* wire, screws, spaghetti, etc. Quarter lb reel of 28 gauge D.C.C. wire. 100 ft of 34 gauge D.C.C. wire. Winding the Coils. About three-eighths of an inch from the end of one of the tubes drill two small holes, loop one end of the coil of 28 gauge wire through these, and wind on 90 turns. This is coil B in diagram.

While three valves have been shown it is quite possible to acid another stage of audio frequency amplification, and builders who cdntemplate making this addition in the future should purchase

a 21-inch panel and cabinet instead of the one specified. Apparatus Required. Tile following is the apparatus required in the construction of the Sun Thrfee One panel 7 x IS inches. One cabinet to fit panel lOin deep with baseboard. Three variable condensers .00035. Two Vernier dials. One plain dial. One Yaxley filament .switch. One dubilier 1 ohm fixed resistance with mounting. Three tube sockets of the cushion type. One six-wire battery- cable. Two pieces of bakelite, ebonite or composition tubing 2in in diameter and sin 'Diree .006 fixed condensers. One bobbin to fit inside 2in tubing, wiih slot 1-Sin wide and 3-16 in deep. This maybe of wood or ebonite. One choke of first-class make. One Ferranti transformer, AFS or AF6. One single contact jack. One fiash lamp cell 1 ' volts. One C. battery- 41 volts. One C battery 22f volts la small B battery i.

.It will be best to have someone hold the spool and keep a tension or. the wire while it is being wound. Fasten the wire as at the beginning. Leave quarter inch space, and then wind a second coil (A in diagram) of 30 turns, taking out taps at 10 and 20 turns. Take the second tube and wind 90 turns as before. Leave about an eighth of an inch space and wind on 30 turns ; in the same direction as the first coil. This completes coils D and E. i To wipd coil C, fasten one end of the 34 gauge wire to a hook in the wall, run out 30 feet of wire, get someone to hold it at this point, and run another 30 1 feet back to the hook, cut the wire and fasten to hook. Now place a picture j hook in the hand drill and place the loop over hock. On turning the drill I the wire will be twisted, and this should be carried out until there are about ! five twists an inch of w ire. Now icniove the wire from hook and I very gently give the twisted w ire a

slight pull. Tills will prevent ft from kinking when the tension is released. Drill a small hole near bottom of slot in bobbin and insert end of double wire through it. Keeping a slight tension on wire wind on 17 turns. Fasten the end of wire by passing through another hole made in rim of bobbin. You now have two wires coming out of each hole. See that the wires are not touching, and then test for short circuits as follow's: Attach one terminal of your speaker or telephone set to one end of a C battery, then a wire from battery to one of the wires from bobbin. Complete the circuit by connecting a wire from speaker to the wire from same hole in bobbin. If there is a click, then coil is shorted and must be rewound. If, however, theie is a very faint or no click then coil is correct. Now remove the connection from one of the bobbin wires and connect to each of the wires coming from second hole. One will give a click, the other will not. The one that does not give a click must be solderea to the one coming from first hole, to which connection is made. This is the centre of coil and is connected to R battery. It is immaterial which of the remaining wires is connected Vo plate and neutralising condenser. Baseroard Lay-Out. Mount the tube with coils A and B in a vertical position as near the left as possible, either with a small brass bracket or a piece of wood. Brass

! screws must be used. The second tube ■ , is mounted in a horizontal position in i a straight line with the first and raised i from the base by means of wood blocks i |so that toe cemie of the tube passe? ■ | through the centre of coil B. ) ' The transformer should not be holding coils I) and E. but tc one side ) mountc' in front of the end of the cube ! j The remainder of the lay-out requires - j no attention, except that the two tubes ! containing the coils must not be closer ’ i than seven inches at their nearest points. Pan el Lay-Out. 1 The panel lay out is very simple. One ) condenser with vernier dial is mounted 1 on the left of panel; the second also ? with vernier dial about eight inches to ? | the right. The legrneration condenser I can be mounted to the right of the seci ond one, lca-.mg about three inches at l the nearest p-»inl (see that the plain i dial does not touch vernier before drill--1 ing holes). The jack and filament switch i' can be on right of panel.

Wiring the Set. Owing to the absence of rheostats the wiring is not very intricate. Commeuce by running the filament wires. Then start at the aerial circuit and work to the right. The aerial connection will have to be left until the machine is tested. Be careful to make the connections to coils D and E, exactly as shown. Use bare hu, bar wire and not tlie thin covered wire that is told in coils; it is hard to make a good job with the latter. Tubes to Use. The following tubes should he used: For. the RF an A 409, detector A 415, audio a 8403. The positive of the G battery must he connected to negative filament; then the negative of C battery to the positive of a 22 volt B battery. The negative of the B battery (which is being used as a C battery) goes to the grid bias or F terminal of transformer. If desired a B*os can be used in the last stage instead of the B 403: this tube however w’ill not handle so much volume, but will on 1:/*require 14 volts bias in addition to the 4$ volt C battery, or 13 volts in all. Unless the correct bias is used the B batteries will soon lun down, and there will be distortion.

The grid bias from dctectcr goes cither to the 14 or 3-volt tap, as desired. With the higher voltage a higher B battery voltage will be required in the plate circuit of detector.

Toting the Set. Having checked all connection connee* up anil insert tubes, and attach aerial connection ‘.c top of coil A. Now . turn iexoneration condenser and see if detector oscillates. If it is not, s>» that coils !) and K ?ie wound in the same direction, and that connections are correct Trv s/.1-ir.g B bat:erv voltage. Now pick up 2YA and tune-in carefully. Remove positive filament wire from first socket. Then if 2YA can still be he* rd adjust neutralising condenser , until it disappears, and replace connection. I" receiver is not selective try .aerial connection on one of the taps. Sold*'*’ i to correct tap. Try making slight varla- , lions in C battery soltape* until purest •j reception is secured. Lack of selectivity may be caused by too many turns on coil C. The receiver will <»n good evening* briig in Australian stations with fair i volume. It is not. however, intended | to be a long-distance machine.