THE SUN FOUR

Sun (Auckland), Volume II, Issue 332, 18 April 1928, Page 14

THE SUN FOUR

Simple To Build, Low In Cost, High In Efficiency

THF. set builder who desires to build a machine capable of -ivinc loudspeaker reception of Australian stations, is faced with either purchasing a set of ready-made coils and transformers, or else using makeshift apparatus of low efficiency, due to lack of proper tools. In the following article Mr C. R. Russell, M.S., tells how to build an efficient four-valve receiver which can be constructed by anyone having a slight familiarity with radio apparatus and a drill and soldering

The “Sun Four” is a receiver employing one stage of neutralised radiofrequency amplification. a detector with capacity regeneration, and two stages of audio-frequency amplification. The transformers—always the source of difficulty—can he made in less than half an hour and without any special tools. The machine when finished will give results equal to that of the Browning Drake, while the cost of the completed receiver is from £7 to £9. according to the make of apparatus chosen. Fallowing the writer’s practice of not describing a receiver in these columns until it has been thoroughly tested, the experimental receiver was built several months ago, and has on most evenings y

throughout the summer brought in the Australian stations with good strength. Apparatus Required. The. apparatus required is as follows: Tour inches of 2sin tubing; five inches of 2*in tubing; three .00035 MF variable condensers ; four UX type sprung valve sockets; two vernier dials; one 10 ohm rheostat; one filament switch; one single telephone jack (a double jack is also required if it is desired to cut out last tube) ; one .0001 fixed condenser; two .005 fixed condensers; one 4-1 audio frequency transformer; one 3-1 audio frequency transformer; one Bremer Tully neutralising condenser; one 1* volt flashlight cell; two 4$ volt C batteries; two or three 45 volt B batteries; one 4 or 6 volt storage battery (according to tubes used) ; four valves (see text); one 7 x 18 inch panel; nine terminals; assorted bus bar wire, screws, etc.; baseboard 18 x 10 inches; coil 30-gauge wire, coil 36-gauge wire, both D.C.C. The Transformers. The first thing to do is to wind the transformers. Take the 4in length of tubing, and wind on 70 turns of the 30gauge wire, taking out a tap at the 15th turn (coil A). On both coils fasten the ends of the wire by boring two

small holes and lacing the wire through. Take the second length of tubing, and starting about a quarter of an inch from the end wind on 30 turns of 36gauge wire (coil B), taking out a tapping at the centre or 15th turn, fasten the end, leaving an eighth of an inch space, wind on 70 turns of 30-gauge wire (coil L), in the same direction as the first, or primary, coil, then leaving three-sixteenth of an inch space, wind on 12 turns of the 36-gauge wire in the same direction (coil D). taking out a tap at the sixth turn. The transformers are now completed, and it only remains to assemble the set. Take one of the variable condensers and mount it on the extreme left of

panel, the second condenser sliould be mounted nine inches on its right, the third condenser being mounted about four inches from the second. The rheostat, filament switch and jacks can be mounted on the extreme left of panel, or in any convenient position. Coil A, the aerial coupler, should be mounted on the extreme left of baseboard and jn a vertical position. The i RF socket is close to it on the right. The tube containing coils B, C. and D. should be mounted in front of second : variable condenser in a horizontal • position, and in line with coil A. The ; detector socket is placed on the right ’ of the RF transformer, then the 4-1 . transformer, the first AF socket, the 3-1 transformer, and then the last, or power, socket. Wiring. The wiring is so simple that a detailed description appears unnecessary. Commence by joining up the negative terminals of all the sockets, a wire connecting them with ground, minus A, minus B. and plus C of the batteries. The rheostat must be in the positive

> filament lead with the filament switch. The aerial terminal goes to the tapping at the loth turn on coil A. after passing through the .0001 condenser. Be careful to connect the wires from coils B, C, am! D exactly as shown in diagram. The connections of coils C and D are particularly important, as if these are not correct the detector will not oscillate. Note that the rotor plates of the variable condensers all go to negative filament. If it is desired to use a jack for cutting out the last tube, purchase a four-contact double circuit jack. The plate of the first AF tube goes to the top contact on jack, the P on transformer to the secdfcid. the B on transformer to the third, and the 90-volt B terminal goes to the fourth. The Sun Four will work with any standard tubes having the same filament voltage. If a 6-volt battery is to be used the UX2OIA tubes should he used; if, however, a 4-volt battery is desired, then use Phillips’s A 409 tubes in the first three sockets, and a 8406 in the last stage. A 8403 power tube can also be used in the last stage, but it is then necessary to have a 20-volt C battery, Tf a power tube is desired on six volts the UXII2 is available, requiring a C batterv of nine volts. Operation and Testing.

Having checked the wiring carefully, connect the terminals to the respective batteries, and the aerial and earth connections, light the filaments, and plug in loud speaker, with the third, or regeneration, condenser all out, adjust the two condensers until 3YA is brought in. Now slowly rotate the tuning dials until 2YA is picked up; it will be noted in all probability that there is a howl when the two condensers come into tune. Should this not take place, turn in regeneration - condenser until detector oscillates slightly; now note if turning the left-hand condenser causes a squeal. If it does, adjust the neutralising condenser with a piece of wood pointed like a screw-driver until the squeal stops and only a rushing sound remains. A better way to neutralise is as follows. Tune in Wellington, then replace the first tube with a burnt-out one of the same make; using a head set. the station will probably still be heard. If not, bring up regeneration condenser. Adjust the ' condenser carefully until the station is as loud as possible, turn the neutralising con-

denser with the piece of wood, until the signals disappear. The set is now neutralised and the tube can be replaced. Faults. Failure to oscillate is generally caused by coils C and D being connected the wrong way, or one of the coils having been wound in the wrong direction. In some cases it may be necessary to apply 67 volts to the detector plate instead of 45 volts. Failure to neutralise mav he caused by too many turns on coil B, coil A and the RF transformer being too close together, too long grid and ! wires, or untidy wiring. When using Phillips’s tubes it may be possible to increase the number of turm on coil B with increased signal strength Ihe tone of this machine depends on the quality of the audio-frequency transformers, and the correct C battery voltages. If large core transformers, such as the Ferranti, are used, together with a power tube, then the tone will equal that of any factory-buiit sqt on tne market. Beginners need have no fear in building this machine, as the ease of construction is remarkable, and it the directions are followed carefully, an excellent machine will result.