RADIO REVIEW (101 Year L Publication)
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1 AND RADIO REVIEW (101 Year l Publication) No. 347. WEDNESDAY, APRIL 7TH, 1926. VOL. XVIII. No. 14. Assistant Editor: Editor: Assistant Editor: F. H. HAYNES. HUGH S. POCOCK. W. JAMES. Editorial Offices : x39 -4o, _ FLEET STREET, LONDON, E.C4 . Telephone: City 4011 (3 lines). Advertising and Publishing Offices : DORSET HOUSE, TUDOR STREET, LONDON, E.0 4 - Telephone : City 2847 (13 lines). Telegrams ; " Ethaworld, Fleet, London." COVENTRY : Hertford Street. BIRMINGHAM : Guildhall Buildings, Navigation Street. MANCHESTER: 199, Deansgate. Teleprome: "Cyclist Coventry." Tekgenms: "Autapreee. BIr n:ngham." Telegrams: "Mile, Maneheeter." Telephone: 10 Coventry, .Telephone: 2970 and 2971 Midland. T.,kphone. 8970 and 8971 City. Subscription Rates : Home, £t is. 8d.; Canada, £t is. 8d.; other countries abroad, £t 3s. tod. per annum. As many of the circuits and apparatus described in these pages are covered by patents, readers are advised, before making use of them, to satisfy themselves that they would not be infringing patents. CARELESSNESS IN MANUFACTURE. OSCILLATION : IS THERE A CURE ? VERY manufacturer of repute takes pride in the E were sorry to see, some days ago, an un- t quality of his products, and one usually finds that W authorised statement in the daily Press regarding in a well- conducted business this pride is reflected in the a wireless invention which; it was stated, was due to Sir work of the entire staff. There are instances, however, Oliver Lodge. Fortunately, attention was drawn to it when it seems that some un- in time and a correction was issued accountable slackness develops in in most sections of the Press on the organisation, which permits CONTEN7'S. the following day. of very serious deviation from the PAC. r. Sir Oliver Lodge is, apparently, EDITORIAL VIEWS ... ... ... 511 standard of quality which the .It work on the interesting problem BROADCAST RECEPTION WITH FOUR - manufacturer has set up. We of the prevention of radiation ELECTRODE VALVES ... ... ... 512 would urge manufacturers wire- from receivers. of By F. L. Devereux. The statements less apparatus to pay greater made in the Press would have led TELEPHONY ON TRAINS ... ... 517 attention than is done at present one to believe READERS' NOVELTIES ... ... 520 that no receiver cap- to checking the standard of their able CURRENT TOPICS ... ... 521 of producing this desirable products. Several instances have PORTABLE RECEIVERS ... ... 523 result had so far been developed.. come to our notice recently which By The Wanderer. This, of course, is not the case. indicate that even amongst the We PRACTICAL HINTS AND TIPS ... ... 525 know that in the early days of best -known firms, really serious LOUDSPEAKER .. 527 broadcasting the Postmaster - cases of carelessness CONNECTIONS can occur. By A. P. Castellain. General prohibited the sale of sets As one example, we have informa- SINGLE SIDE -BAND TRANSMISSION capable of causing interference in tion that out of a certain order (Continued) ... ... 529 this way, whilst very many devices placed with a responsible firm for By E. K. tSanaeman. have been described in The Wire- a dozen grid leaks of stated value, BROADCAST BREVITIES ... ... 533 less World from time to time no less than four out of the dozen NEW APPARATUS .. ... ... 535 which prov -ide a means of achiev- proved to be blanks; in other WIRELESS CIRCUITS IN THEORY AND ing the same end, even though the words, the resistance value was PRACTICE .. ... ... ... 537 receiver itself may he in a state of practically infinity. Imagine the By S. O. Pearson. oscillation. The reason that sets annoyance and trouble that might LETTERS TO THE EDITOR ... ... 540 incapable of causing interference well be caused to some unsuspect- READERS' PROBLEMS ... 541 have not come on the market is ing purchaser of such an article, that some loss in efficiency results especially if he were not in a from the introduction of methods position to detect the fault for himself. One serious dis- to combat the evil or else an additional valve stage is appointment in the quality of apparatus purchased will required. If Sir Oliver Lodge's experiments produce a scarcely be overlooked by the victim, even though he may circuit which is effective, with even a single -valve oscil- have had long and satisfactory dealings previously with lating set, then he will have contributed another important the same firm. Confidence once lost is not easily regained. invention to the progress of wireless. but unless such a We hope that, by timely notice, steps will he taken by scheme is applicable to simple sets without expense or corn - manufacturers to see that no occasion will arise in the plication, we believe that we shall still he as far off from future for drawing further attention to the matter. a solution of receiver oscillation troubles as we arc to -day. 8 A 9 www.americanradiohistory.com 512 Wip®boo APRIL 7th, 1926. WopIlcol ./VVVVV` w ry .yr.-j + " 1-1..1.-P.-.M * r1 v I N ara aar, fa al.. i J .ti.-1.Ii.la. i ia QC WITH-2-e-;" ÑI ÑI Ì1H \%LlÌ VÑ\ i vÌÌIl-ÑÌ V AO/. ÌVÌ.a. i aa... +..111 A Receiver Using a 10 Ampere =hour Accumulator H.T. Battery. By F. L. DEVEREUX, B.Sc. TH E high- tension batter introduces an element. ut case there is the question of transport to 'the charging uncertainty into the otherwise satisfactory perform- station, to say nothing of the high initial cost. ance of the modern broadcast receiver. Quality of The use of 4- electrode valves, which, when suitably reception is good, valves are reliable, and the charging of connected, require a maximum H.T. voltage of only 15 the filament battery every week or so is now taken as a volts, puts quite a different complexion on the matter. matter of course ; but unless one is fortunate in having Only seven or eight cells are required instead of sixty, D.C. lighting mains at hand, the H.T. supply after the and it is possible to increase the capacity of the cells ten- experience of the first two or three breakdowns becomes fold without producing a battery of undue weight or cost. to the listener a never- ending source of anxiety. It is D.T.G. cells lend themselves admirably for this purpose ; true that the larger firms who have been specialising in a battery of eight cells costs 36s. (less than the cost of the production of dry cells for many years are able to a 120 -volt dry battery of first -class quality), and in the prdoùce a reasonably reliable battery, albeit at rather high receiver about to be described gives 2,000 hours' service cost to the consumer. This cannot be said of the average on a single charge. It can then be recharged at a cost dry battery with small cells, which is highly unsatisfac- which ought not to exceed 2s. 6d., and, owing to the tory; you may get one to last six months, but more often special nature of the plates; will last almost indefinitely. than not it will break down after six days due to a Here, then, is one solution of the H.T. problem. Let faulty cell. us now turn our attention to the design of a broadcast receiver employing 4- electrode valves and an H.T. battery H.T. Accumulators. of D.T.G. cells. As an alternative, the H.T. accumulator may be con- General Design sidered. In general the cells are too small, and if power valves are used the H.T. accumulator will need charging As reliability is more important to the broadcast listener every time the filament battery is recharged. Careless than to the experimental amateur, the requirements of the charging will soon ruin these small batteries and in any former have been kept in mind and the receiver has been designed with the object of 1,{ keeping the number of ad- LP justments as small as pos- 000 op - sible. A sketch of the 0000 complete receiver as it ap- ts o.s pears when finished is in- o eluded in the title of this .__. article. It will be seen 0-0003 mfd -- that the only controls which are visible are the key GB switch for changing over 2M n2 + from the local station to Daventry, and a push -pull switch for the filament current. The tuning and re- action controls, once set, -LT require no further attention T- so long as the wavelengths of the stations remain con - Fig. 1.- Circuit diagram Attention is drawn particularly to the method of stant. Two small doors switching the tuner. have therefore been pro- 20 A Io www.americanradiohistory.com APRIL 7th, .7926. Wñp@ftwo WopIlcol 513 Broadcast Reception with Four -electrode Valves. - and a con iiderable step -up of voltage between the detector vided to cover the tuning dials with which one might be and 1.. F. stages is thereby obtained. No by -pass tempted to interfere were they con- visible. Removal of the denser is shown, but one having a value of o.00r mfd. back Of the cabinet reveals the three valves which are in may be connected across the primary winding if there is a compartment to themselves, and above them another any difficulty in making the receiver oscillate on the compartment containing the L.T. battery. The receiver Daventry wavelength. may therefore he operated, the L.T. battery charged, and An examination of the characteristic curves valves renewed without interfering of the in any way with D.E.; four- electrode valve reveals that with the maximum other parts of the receiver. The Circuit. In order to tune to the local station and also to Daventry, two separate tuned circuits are connected in series in the aerial circuit.