Full Constructional Details of "The SUPER SIX"

Radio Record, Volume V, Issue 22, 11 December 1931, Page 16

Full Constructional Details of "The SUPER SIX"

By

the Asst. Technical Editor

AST week’s instalment ‘of the description of this receiver was mainly occupied by an outline of the principle on. which the "Super Six," and. in fact, all superhets, work. A list of parts and a theoretieal circuit was also given,’ so that the constructor could become’ familiar with the details of the set. This week we propose to deal mainly witb the actual construction. Not the least remarkable of this set’s qualities is the ease with which it may be constructed. Several years ago we would never have dreamt of advising: anyone unversed in the art of radio to begin by building a six-valve super~ heterodyne. The fact that we do so now is an indication of the tremendous strides which have been made in receiver design over the last few years.

_» The first task, after procuring all the necessary components, is to drill . the baseboard to take the six valve holders, Which are mounted through it, It will save much trouble if this is purchased ready drilled. The operation may be quite easily performed, how"ever, by describing the required circles, which will be about ifin in diameter, depending upon the type of valve base used, and then by going round just inside the circumferences with a drill . until the centre portions can be taken out, The circles can then be trimmed . up with a pocket knife. After. these six sockets have been ' mounted, the remainder of the above baseboard components can be placed in ‘position and screwed down. All the necessary dimensions are given in the lay-out sketch. It will be necessary to ‘ solder angle brackets to the oscillator

coil, i.e, that nearest the front panel, so that it may be serewed down to the base, A point here concerning the mounting of the English valve sockets, which take the three intermediate frequency transformer coils. It. will be noticed .from’ the lay-out sketch that the two on the extreme right are not in the same relative position to the valves as those shown in the photograph. This is because, in the original model (a photograph of which appears on this page) super het. coils of foreign make were employed. ‘The leads coming out on top.of the cans of two of the coils are longer than those used in the English type of coil. As the latter did not arrive until the original model of the "Super Six’ was built, however, this was not discovered until after the photograph had been taken. The later coils, however, which are now, to our knowledge, the only ones available, have since been incorporated in this set by shifting the two valve holders in question along to the right. No other change in lay-out was involved. We mention this point because the wiring on the constructor’s set may appear a trifle different from that shown by the under baseboard photograph, and it may be throught that a mistake has been made, It will be noticed, however, that the wires from the two valve sockets in question will be merely shifted along an inch or so to the left. Under Baseboard Components. ‘THE baseboard should now be turned ‘over and the under baseboard components mounted. All the connecting wires_are clearly shown in the photograph, those passing through the baseboard being indicated with correspond_ing numbers above and below, so that no possible,error can be made. When the wiring is completed, however, it should be checked over from the theoretical diagram, The distribution strip toward the top left of the photograph is not absolutely necessary, for the various wires in the battery cable may be run straight to the designated positions, but by its inclusion the wiring is much neater and more businesslike. It will be noticed that three spaghetti re-

‘gistances are used. These are incorporated to give the necessary voltage drops at the different points of the set. Volume is controlled by another resistance in the: form.of a potentiometer, which operates on-the screen-grid voltage, It will be noticed that in series with this, ‘on the positive side, is a 20,000 ohms resistance. If this were not used there would always be a danger of appi,.ims too much voltage to the screen-grids. ‘It may be wondered why we have included a three-point on/off switch. It will be noticed, however, that whether the filaments are on or off the potentiometer.is always across the "B" battery, and hence, unless the circuit is broken, it is always drawing current, which, by the way, is in the neighbourhood of two or three m. amps. Though small, this drain is constant, and would materially shorten the life of the "B" batteries. Hence a three-point on/off switch is employed to break both the filament and potentiometer circuits. The panel components should now be mounted. Notice that the screening box surrounding the tuning condenser on the left, looking at the panel, does not touch the baseboard screen, This/ is important because this box is in contact with the moving vanes of the

variable condenser, and because of the 14 volts grid bias on the oscillator valve it;#is at this difference of potential fyém the baseboard.. This point should be carefully watched. gyotice also that the three screening cams of the intermediate frequency transformers, which are earthed internally, oe not be earthed externally, no2 ould they be allowed t») touch, The Wiring. HEN the front panel. has_ been ° mounted on the baseboard by | means of three screws, the receiver is ready to wire. Notice that the three | filament terminals nearest the panel on the valve holders used for mounting | the coils are earthed by taking a short wire from each to one of the screws which hold the valve holders to the baseboard. ‘This is clearly shown iu the layout. sketch.. The various wires running to the distribution board should be tagged as shown in the photograph to avoid mistakes, hnd similar tags attached to the other end of the wires where they emerge from the battery cable. When the wiring is completed it should be completely enclosed with an alutninium base of the dimensions

of the chassis, and with a small turnover all round to enable it..to be bolted into position, This additional screening, like that surrounding the oscillator condenser, is vitally’ necessary to prevent radiation from the receiver and resulting serious interference with other nearby sets of the same type. Failure to comply with these instructions constitutes a_serious breach of the P. and T. Regulations, and confiscation of the receiver would sooner or later result. : The Frame Aerial. AFTER the wiring has been carefully re-checked, the set is ready for operation. . The frame aerial should now be wound according to the dimensious given in the sketch, These are not eritical, and as long as about 75 feet of wire is employed, with turns spaced about 3-16in., the given design may within limits be altered to suit individual requirements. aa For best possible: results Litz wire should be used, but we have found that ordinary silk-covered 23/36.. frame aerial wire answers the purpose excellently. . 2, One end of the wire is attached to either outside terminal on the frame. and the winding commenced...: Seven turns are. put. on, spaced 3-16in. dy means of small saw-cuts made with a hacksaw in the supports. The wire is then anchored round the lowest support, bared for about 4in., and a turn taken.round the centre terminal. Seven more turns in the same direction are then put on on the other side of the frame, and. the end attached to the remaining terminal. Three lengths of

flex with banana sockets at the enils should then be attached to the three: terminals. The frame is now complete and ready to connect to the set. ‘The Valves. HE "Super Six" works equally well: with valves of the following types: Oscillator, L210; ist detector, H210; 2nd detector, L210; power, P215; andtwo screen-grid valves of the type S215, "B" voltages are also not critical, "HY « 1" should be about 90-100 volts, ~ and "HT 2," 120 volts, As:mentioned- be- «

fore, the other necessary voltages are’ : obtained by the three spaghetti type resistances and the 50,000 ohm poten‘tiometer. _ Operating the Set. AFTER the set has been wired and the wiring checked, paying particular attention to the filament. and plate circuits, the frame aerial, batteries, and speaker may be connected and the valves plugged in. Jf'the constructor is not certain that his wiring is correct, a preliminary test _(Concluded on page 30.) Cc e

The "Super-Six"

(Continued from page 17.) of the’ filament ¢ircuits, while both "A" and "B" batteries. are connected, should be conducted with a torch bulb of the same voltage as the valves used. A piece of insulated flex should be twisted round the Aase and -the bulb held upright..on the chassis, while the free end of the wire is inserted in the "A+" sockets of the valve holders. If it lights up in each and does not burn out, the valves may be inserted. Bias voltage for the oscillator valve will. be eithér 13 or 3 volts, while that

for the power valve should be ascer- i tained from the leaflet. enclosed ' "in" the. valve carton. ‘ To operate ‘the set,: the screen grid potentiometer should: be ‘advanced about half-way, and the two tuning

dials slowly rotated in step, a condition which may be ascertained by a "live" sound from the speaker, Control volume with the potentiometer. If the set operates correctly, and if care is taken in the wiring, there is no reason why it should not go at-the first try-out. You will be amazed at the ease with which station after station may be tuned in. ; : Lastly, we would much appreciate any reports on the performance of this set. These will be published for the purpose of enabling other constructors to compare results and to ascertain if their own sets are working properly.