The "OUTSPAN FIVE"

Radio Record, Volume IV, Issue 32, 20 February 1931, Page 16

The "OUTSPAN

FIVE"

Simple, Powerful and

| Economical

Developed from the

"Browning Drake"

By -the

TECHNICAL

EDITOR

1] HIS set has been brought out )}} at ‘the: request of a large number. of readers who wanted an- up-to-date version of the ‘ "BrowningDrake" circuit. There are several features: that have been changed from -the original, and their changing means’ that the original Browning-Drake is virtually non-existent. ‘ However, in the course of the description the method by which the older B.D.’s can be adapted to the circuit will be fully described. The new features are the differential method of controlling reaction and the ean method of shielding the coils7 At this stage we have not reduced the

(dials to one; mainly owing to the fact that there is some considerable difiiculty in matching coils. Coil matching is not-a difficult. proposition when there is no reaction, but its use introduces .complications, and, to be ‘quite frank,. at the present ,we have not * been able to successfully balance the ‘three coils. The first two do not pre-sent-great difficulty, but the condenser controlling the detector coil is as much as 10deg. out at the. bottom of the scale, although it is right in phase at the top.. However, this difficulty will be overcome, and in a short time we shall bring out a single dial, or, at the most, a-two-dial réceiver. We used differential reaction because it is best. Not only does it give smooth control, but it can be operated more . easily than the older methods, with the result that oscillation .can be minimised. With the screen-grid valves, the constructor need not be afraid of annoying his neighbours. Another feature of this set is the provision of a third aerial tap leading in through a fixed condenser to the primary of the detector coil. This means that at the required station the

two screen-grid valves can be cut out and a saving of power thus effected. Country listeners in favourable districts will also find this a great boon. Ample ‘space has been allowed in the lay-out for’ varying-sized components and for yariations in the lay-out. We suggest, however, that as-far as possible our specifications be adhered to. A list’ of. components is given and the constructor is advised to purchase them all and to carefully examine them to see that they are exactly as specified, and are in good. order. : The Baseboard. TNE first actual task is drilling the | panel. The position of the three (dials, the two knobs, the switch, and

the, speaker plug can. be seen. Muy clearly. from photograph 2, the front | aspect of the set. The three dials are 4in. from. the bottom and separated by 5hin.. The rheostat on the left and the > reaction control on the right are also 4in. from the bottom. The switch on the left and the plug on the right are ‘Sin. from the bottom, and immediately under the rheostat and reaction control respectively. Having drilled the holes, fasten the rheostat, the reaction condenser, and the condensers in position. . The next task will be to lay out the components on the: aluminium sub‘panel; This requires some care, as although the parts are not crowded, still the, constructor must remember that

= SONOURON 11, 12. 13. . Earth terminal of aerial coil, Shield. Aerial terminal of coil, Grid terminal first r.f. valve. . Grid terminal of first r.f.. transformer. . From rheostat. . From switch to rheostat. . Sereening grid of first r.f. valve. . A- first r.f.‘valve. A-- first r.f. valve. A-- second r.f. valve. A-- second r.f. valve, 14, Sereening grid second r.f. valve, 15. Grid of second r.f, valve,

16, Grid terminal of second rf. coil. 17. Grid leak and condenser, coil side. 18. A+. detector valve. -19,. A- detector valve. 20. A+ first audio valve. 21. A- first audio valve. 22. A-- second audio valve. 23. Differential condenser fixed vanesg 24. Differential condenser fixed vanes. 25. Differentizl condenser moving vanes. 26. A- power valve, 27, Plate terminal of power valve. 28. Plate terminal of detector valve, 29. Plate terminal of regenaformer,.

"shiealls: have to. come into position. A general idea of the lay-out can be obtained from photograph 1, Coils and ‘transformers are placed in line at the back of the set, while in another straight line some 4in. away are all. the valves. They are quite in order from the first radio frequency to the power valve. See that the valve sockets ‘ are turned round in the right direction. : All filament terminals face.the panel, while the grid and plate lie in a straight line on the more distant side. Winding the Coils. HE coils should now be wound. Divide a foot of 2in. tubing into ' three lengths for the secondaries and ¥ 1#in. tubing, 6in. long, into three sec-

tions for the primaries. The method of winding the coils is left to the constructor, each one of whom will probably have his own ideas. We find the easiest way is to start by drilling two fine holes and threading the wire through these, then wind on the required number of turns and finish off through two coils. It is an advantage to bring out the ends at certain specified places, as this simplifies the wiring. For instance, in the first coil, the top and bottom are brought out on the one side . and solder lugs attached quite close to one another.. When mounted these will. face the panel. The number of turns on this coil when wound with 26 gauge wire is 75. : In winding the first r.f. coil the top is brought out on one side and the bottom about iin. further round and as close as possible to the point where the foot is to be attached. This end is earthed so its proximity to the foot will be a decided advantage. On this coil are wound 80 turns. For the third r.f. coil a little space must be left at the top on which to wind the reaction coil. The bottom and top of the main coil are brought out quite close together. Seventy-five turns should be wound on this secondary. Leave a space about 1-8in. and. wind on another 30 turns of 32 s.w.g. wire; bring the ends out about lin. round from the secondary terminals. When mounted these two will be between the back of the set and the two secondaries toward the front and left. The primary coils are now wound separately. For the aerial coils 25 turns of 34. gauge are wound, the ends threaded through the former and brought out ready to be attached to solder lugs on the. main former. Both ends should be near one another, The same applies to the other three coils, but 30 turns are wound upon each. All coils are wound in the same direction. In mounting the primary inside the secondary former some means of holding it in position will be required. We have found that little pieces of ebonite tubing are quite useful for this purpose. Roughly speaking, the bottom of the primary coil should come opposite to the bottom of the secondary coil. In the case of the first coil turn the former round until the two ends are opposite the two lugs already on the former, These are then taken out to solder lugs. The bottom of the aerial coil and the bottom of the secondary coil are joined and these are earthed, a suitable connection for which may be the foot that is attached to the coil. In the case of the secondary coil, the small former is arranged so that both taps come out to the back of the coil,

that is, the side directly opposite to its existing terminals, In the third coil the two must come out close to the two ends of the main coil. When this coil is placed in position these four terminals face the panel and the two regeneration taps are at the back. If English type screen-grid valves are used, the top ends of the second and third coil are connected to flexible leads which are taken to terminals at the top of the valves. If American valves are used these go to the appropriate plate terminals on the first and .second rf. valve bases and. the tops of the main coils are connected with the terminals on the top of the valves. A suitable connection may be made from the fixed plates uf the moving condensers. ’ The diagram of the third coil will be of considerable assistance to those who make their own coils. Those who do not feel equal to the task (it is really quite a simple one) can obtain them already made for quite a very reasonable sum. Cut a piece of ebonite the length of the sub-panel and l}in. deep. On the

left hand end drill 10 holes and mount the terminals. The designations of these are quite clearly seen: from: the _ photograph showing the underneath wiring (4). On the right hand end drill two holes for the aerial and the earth. Two pieces of jin. timber will be required for the _ sides of the base. These will be 94in. x 1}in. Fasten the aluminium to a piece of three-ply of equal size and ‘mount panel and sidepieces. Angle brackets will hold the panel and sub-panel together, as can be seen from the photographs, Actually the aluminium sub-panel will be iiin. from the bottom of.the front panel, This is to allow for wiring and components to be placed underneath and to protect the wire from damage. -At this stage fit the valve sockets and the coils and transformers on the subpanel in the positions indicated in tke photograph. These are bolted right through the threeply and the aluminjum. The grid-leak and the condensers: are likewise attached, but there is, no (Concluded on page 29.)

80. Plate terminal of first audio transformer, ; 81. Grid terminal of regenaformer. »2. B regenaformer, 3. Regeneration coil, 34. Regeneration coil, 5. B+. first audio transformer. 6. GB. first audio transformer, 7. End of secondary regenaformer (det. return). . 8. B+. second audio transformer. 9. G.B. second audio transformer. 0, (Between condensers reading ‘4’’) B-.. second r,f. transformer.

1 "Qutspan Five" \ Se ieenhaemeeete . (Continued from page 17.)

need to.drill right through, just pierce the aluminium and-serew them to the underlying timber. ‘The positions of the condensers, the ¢hoke, switch and the jack can bé séen from the photograph depicting the underneath wiring. Place these in position and screw them to the threeply with jin. screws. Everything’ should now be in position

ready for wiring. At the points indicgied by numbers in photograph 4, d right through the sub-panel and bottom to allow the wiring to pass through without touching.

Wiring the Set. A POINT to point wiring description will not be given because it would bé more confusing than helpful. Photograph 4 and the table that accompanies it will givé a clear indication where every Wire is to go, while photograph numbér 8 shows where the wires on top of the sét go. Remember, if Mnglish valves are used, the description as We have given holds. If American valves are used, the bottom end of the primary connects With P of the first and second valve respéctively, G of the valve sockets is the auxiliary grid and the point on top connects with the fixed plates of the first and secondary condensers respéctively. ae Operation. [Pan operation of this set is really very simple. There is no néutralisition, and it should be found -to oscillate without any difficulty. Do not keep it in the oscillating stage, as there is a possibility of causing interference. Apart from this, it quite spoils the programme being received. The plate voltages should be as high as possible. The power valve it will be seen is connected with the plates of all valves except the detector. This is in accordance with modern practice, and it will be found to give good results. The voltage on the detector valve will depend upon the capacity of the differential condenser and upon the number of turns on the reaction coil. The s¢éreen voltage should be half that of the plate-usually 60-75.. Our coil has been designed for a .002 differential condenser. If a smaller one is used more turns must be added to the coil. If however, there is difliculty with oscillation a .0001 condenser shunted across the differential condenser should make the set oscillate readily. If the set is unstable, smail shields about 5in. x 5in. should be erected between the three condénsers. That means, of course, that there will

be two shields, A fairly large can shiéld should. be used over the coils, and .if- oscillation is very bad the valvés can be shielded by cocoa tins: This was not found necessary in. our experimental model, although we had to resort to the shields between the condensers. ‘We were more than pleased -with the results that this set gave us. In its initial try-out we were able to bring in without any difficulty all the main New Yealand and Anstralian stations. We had to reduce volume considerably on the main Australian stations after about 9 p.m, whilst in the early hours of éne morning we had three Japanese at really tremendous strength and an American at ‘ery good strength. We have not had time yet to fully explore the possibilities of the circuit. We believe that if it is carefully constructed it will be by far the most powerful battery set that has been deséribed. Its simplicity is one of the stiongest features in its favour. A glance at. the photograplis will assure the veadér that there is réally nothing that will give him any anxiety. Above the baseboard there is vety little wiring, while underneath the wires are direct and not in any way confusing. Our system of numbering the holes and providing a key should meet with the approval of constructors. Wé strongly advise that only the best parts be sed in. this receiver. By tae best we do ot mean elaborate, expensivé, components. Otir sét was built of almost entirely Bnglish parts and was perfectly satisfactory. Converting Old Browning-Drakes. N converting old Browning-Drakes it will generally be necessary to redesign the set and lay it out as we have indicated. Slight adaptations will have to be made in order to use the swinging coil méthod of regenération. The detector coil will. have to bé shifted slightly to the left in order to accommodate the tickler knob, Smaller dials than are shown in the diagram will

have to be used and the knob placed between the second and third. Apart from this adaptation the parts used in the old Browning-Drake will be quite Satisfactory. . Tf selectivity ‘is not. quite. what is desired, try a .0003 fixed condenser in series with the aerial. By using this we were able to separate 2BL and 4YA from the local station. On 4QG and 2FO there was ‘a fairly strong background. We hope at a later date to bring out the A.C. vérsion of this set. —