The "RANGER THREE"

Radio Record, Volume V, Issue 10, 18 September 1931, Page 16

The "RANGER THREE"

Triode r.f. Amplification

lr is some time since a threevalve. set using ordinary triode valves in all stages was -described in the _"Record," and so the "Ranger ‘© Three," which : ‘answers the description,. is quite: an event. . Many. will say’ that this ‘is' a‘ retrograde «set. that .:triedes:-in.. all three stages have ‘been. out :of- date a. long: time We admit this to be true, but there arc a, ‘large number of. constructors who cannot: afford the sereen-grid valves; and who’ must, of necessity, use the less ex pensive triode valves... There is a, larg« number, of course, who have the extr: valye on hand,.and wish to utilise this in their set to turn it from a two tc a three-valve. Another consideration is simplicity, for there is no doubt thai a three-valye.set using a triode r.f. cai be made more easily than can the sam: set using a screen-grid valve. Apar from the neutralisation question ther: igs nothing to: worry the would-be coi structor, and, after all, neutralisatio is a:very simple matter. ‘The ‘old question of single versn multple dials again crops up, and w: have decided that this will be a multip!}: dial set. Those who are prepared t: go to the expense of buying a sing dial -unit will want something more ambitious than the "Ranger. Three." Furthermore, there is that constani bugbear of single dial control-reaction. In glancing over the circuit, those who are at all familiar with the "Ranger Two" will pick up several points of similarity. They will note particularly the method of obtaining regeneration. which is by a .00025 condenser coupled between the regeneration coil and the ground, Furthermore, the audio stage is the same (that rarely varies in any set). Constructors will be interested to know that the detector coil can be adapted from the coil already con. structed, merely by separating a coup of connections and taking a centre tap from the existing aerial coil. This is one of .the reasons why we use the split primary method of neutralisation. Had other methods been employed, it would have been necessary to rewind the coil. Another argument in favour of the split primary is its undoubted simplicity when it comes to the actual

ask of neutralising the set. Experience has shown that the split primary method is always more simple to carry out, and will generally give better resnits. While .00035 condensers have been ‘stipulated for both r.f. and detector coils there is nothing to prevent the use of the .0005 condensers if appropriate

alterations are made in the coils themselves. It will be noted that the first coil-of the set is an auto-coupled transformer, that the separate primary is done away With. This change has been made mainly to bring about sensitivity, for there is no doubt that this method of "oupling the aerial is more satisfactors from the sensitivity point of view than are two separate coils. The :et under these conditions will not be selective. In fact one has to sacrifice a great deal of sensitivity at any time to bring about selectivity, and where a threevalve set is used, there is no power to sacrifice in this manner, so that the

highest possible gain must he had, even if selectivity is to be sacrificed. Bringing in the aerial through a mid‘get condenser is necessary mainly to comply with the Post and Telegraph Regulations. The condenser also improves the selectivity of the set and has the advantage of being able to move dead spots, should any occur. Those who wish to operate the set in a city, or close to stations that operate simultaneously, will find that a simple wavetrap will be quite effective. The employment: of an elaborate' pre-selec-tor circuit cannot be recommended inder any circumstances. The loss of power involved in its use oftsets\ by "ar any gain in selectivity. This set is very simple and even the ‘nost inexperienced constructor should ind no difficulty in making it work. tlowever, we would recommend anyone who is starting out from scratch to make a modern set, not to bother with the "Ranger Three," but to use a sereen-grid circuit such as the "Kestrel Three." This set is merely an elaboration of a previous set for those who made the "Ranger" and were pleased with the result. ‘The added valve will certainly step up amplification. The components for this set are set out in a panel and before commencing the actual work on the set the wouldbe constructor is reeommended to check up this list With the components he has on hand make certain that, wher. all are assembled, he has the gear necessary for making the complete set. Little is more annoying to find when the set is almost complete that one component has been overlooked. Altering the Coils. "THE first task will be the alteration to the existing "Ranger" coil. Make a centre tap on the primary coil, that is, the bottom coil, and separate the end of the secondary and the end of the primary coils. Study the plan of the coil shown in the set lay-out, and you will see that the terminals are in the sume position as they were for the "Ranger Two." that a centre tap (B+) comes out hetween "A" and "OC" and the end of the secondary coil between "P" and G." The connections to "P" and "C" have heen reversed to simplify the wiring. Tf the set will not work with the tickler connected round this way, take them as they were for the "Ranger Two," that is, "P" to the plate and "C" to the choke. The construction of the rf. cols’ should give no trouble. as there is only one winding. This consists of 72

sturns of 26 gauge ds.c. wire wound on a 2in. former, tapped at the twentyfifth turn. Bring the ends out so that they will occupy the positions indicated in the lay-out sketch. When the coils are finished, lay out the components. Do first of all the panel, placing the radio frequency, detector and the regeneration condensers in line, 24 inches from the top. Space them evenly and allow a space of 4 inches from each end for the r.f. and regeneration condensers, and place the detector condenser at halfway, that is, 7} inches. The rheostat and switch are just slightly below the level of the three condensers and to the right and left of the detector condenser. They. should be 5% inches from each end. Mount all the components on to the panel, and then fasten the panel to tue baseboard, either by screws passed through it or by bracketing. The comonents are then placed in the positions indicated in the lay-out sketch and fastened down.

The Wiring. ON the lay-out diagram the wiring has been shown stiff and angular. ‘in order to make the diagram clear. but when the actual wiring is done, the shortest route should always be taken. Note, too, that the battery leads are brought in by cable, instead of being taken out to the more or less old-fashioned terminal strips. This simplifies the wiring and makes the set a few shillings cheaper. Do not be concerned if the negative filament wire happens to go to the terminal marked + on the valve socket. Those marked on the valve socket really do not mean anything. You can take the + or the — to either of the two terminals. You will notice that the output valve appears to be connected’ round the wrong way, that is. the + wire is brought to the one which will most probably be marked -. However, this does not matter one iota. Some transformers are marked differently from the one shown, and, of course, the wiring of the others into the circuit will necessitate certain alterations, but the connections remain the same. . When the set is finished the reader ,will naturally think of the valves he will use. These depend to a large extent upon what he happens to haye on hand, for, as we said before, this set was designed for the constructor who has components on hand and.

wishes to use them. Generally speaking, a general purpose valve can be used in the first stage, followed. by a special detector and a high-gain power valve or general purpose valve suitably biased. Don’t forget the bias on the last valve: it is really very important. If you wish to select the valves for the set, use the following types in.any make and any voltage :- 221, first r.f. and detector, and B605 or B609 in the last stage. If economy of operation is desired, use two 230 valves with a 232 in the last stage. These work from a 2-yolt accumulator and are very light on both. "A". and "B" batteries. The batteries depend upon the valves used and the constructor’s pocket, It is recommended that two-volt valves be used if an accumulator is not available. By so doing two number six cells can be used in series, but as these will have a voltage more than is required for the filament, a resistance will be necessary when the valves are new. This should be about 10 ohms variable and should be kept fully in the circuit to commence with. The number of B batteries will depend upon the amount of cash that. the constructor has to spend. It is recommended that two of the 60-volt type be used. Use the medium-sized batter. ies, for, with a power valve in the last stage, the drain will be 10 to 12 amps. and a small battery will soon run down. The set can be operated from one 60volts battery. The G.B. voltage depends upon the valve in the last stage and the B voltage on it.

From tables, the constructor can ascertain exactly what voltage to make this battery. Outside the set A-, B-, and C+ are eonnected together. B-++- power is the highest B+ available, B+ r.f. is the

next highest tapping, and for that matter may go on to the highest tapping, as well as the output valve. If this procedure is adopted, it may be necessary to connect a imfd by-pass condenser between the tap on the primary coil and earth. This condenser is shown in the theoretical diagram, but not in the lay-out diagram. If the set will not neutralise easily, you must wire this condenser in your set. Neutralising. GELECT a station on about 1YA’s frequency and tune to this until its strongest signal is obtained. Advance the reaction condenser until the set breaks into a whistle. Immediately move the neutralising condenser until the whistle weakens or dies away, then advance the reaction condenser again, at the same time retuning until it again breaks into a whistle. Still further adjust the neutralising condenser until further adjustment of this condenser will not prevent the whistling. The set is now neutralised, and this to a large extent will prevent the set from radiating. However, handle the set carefully, because the neutralising condensers will not stabilise the set on all frequencies.

List of Components for the Ranger Three 2-.00035 variable condensers and dials, 1-.00025 yariable condenser with dial, {-.00025 grid condenser. i-Imfd. condenser (optional). Switch, 50 ohms. Rheostat. Four terminals. Panel, 15in. x Tin. Baseboard, 10in, x 15in. 1 r.f. choke, 3. valve sockets. i-audio transformer. 1-2 megs grid-leak and holder. z-special coils. 6 wire battery cable. Coil of glazite wire.

Coil Specifications .00035 Tuning Condensers. -00025 Regeneration Condenser. 2in, Former, oo R.F. Coil -Secondary, 78 turns, tapped 26th turn. Regeneration Coil.--Secondary 78 turns; primary, 25 turns; tapped at 124 turns; tickler, 35 turns. Wire, secondaries, 26 sd.s.ec.; tickler and primary 28-30 S.C. When .0005 tuning condensers are used, reduce the number of turns on the secondary coil by 10 turns.