Our Correspondents Suggest

Radio Record, Volume II, Issue 43, 10 May 1929, Page 29

Our Correspondents Suggest

R.F. Booster---Neutralising the Two. R.F. UITE frequently correspondents write in with suggestions. Where these have been tried out and proven we shall be pleased to publish them. They may help others, and what is radio when one cannot do that?

An Efficient Booster. A Correspondent (‘J.H."), sends the ~ following description of a booster: "F have enclosed a rough sketch, with éxplanatory notes, re wiring, etc. of a’ booster I am using with my threevalve set. This little piece of apparatus is surprisingly efiicient, and I thought it might be of use to quite a number of your readers. The coil is a coupler type plug in coil (spacewound), range 200 to 550. The basket coils on sale in town for about

2s. 8d. are also efficient for this booster. I use general purpose valves for set, and the booster. I have tried a power valve in booster, but find it is not so satisfactory as the gereral purpose valve. The surprising effect of this booster on my machine is that it is easy to cut out 2YA and get either Auckland or Christchurch stations (without wavetrap). I could not do that before, in fact, I could not get Auckland at any strength on the speaker, although I could get 2BL and 2FC on loudspeaker without the booster. , With the booster attached I get 2BL, 20H, 8LO, 2F0, 3AR, 4QG, 2GB, one Japanese station when 4QG has closed down (JOAK), and, of course, all main New Zealand stations, all on the loudspeaker, and good volume. I have heard also the small Dunedin, 4ZL, station, at loudspeaker strength. No doubt this simple booster is wellknown, but I have never seen it published. Y rough drawings have been done as plainly as possible, and the explanations re wiring have been given in a style that will, I think, be the easiest understood by the amateur who has not any technical knowledge of radio. This style of explaining how to build a set. would, I am sure, be appreciated by others who, like myself, krow practically nothing about radio, but want to build a set themselves as a hobby, but get tangled up with the diagrams, etc., published in nearly all radio papers.

Very few circuits are clear enough to follow (to the man that knows more about a wheel-barrow than radio sets). as the theoretical signs and drawings are not clear enough for him; and so. after studying the circuit, as published by the majority of papers, he says to himself, "I am afraid I cannot build that, as I am not certain of two or three parts, or clear on a couple of points," and reluctantly lets it slide, and he is still making do with his little old set.

PHMMATMAARMIHUUTTUNILUA MUU U HILL ULL LULA Lato Ge Cu Note on the Requirements. The constructor need not purchase a coil. Wind 50 turns of 18 double cotton covered wire round a three-inch former. Wind a piece of empire cloth or greased brown paper twice round the end of this, and wind on 18 turns. This is the primary and the former the secondary. The end of the secondary overlaid by the primary passes to the condeuser and to the grid. A resistance has been placed between filament and the condeuser, but it has been omitted in the layout diagram. In effect a stage of unbalanced radio frequency is being added, and this should give every satisfaction with small sets using detector and two or one audio. Care must be exercised in its operation, for if the rheostat is turned too high the set will oscillate and cause disturbance. Wiring Directions. 1. Aerial post to condenser (C). Condenser to primary coil (the smaller). 2. The other end of this coil to E terminal, 8. Top of secondary coil to moving plates of condenser (to fixed would be preferable.), then to G of valve socket. 4, The bottom of the secondary coil to fixed plates of condenser (moving preferred). 5. The same plates to negative of valve socket and rheostat; this then o AT binding post. From + on (6) socket to A + binding post. 8. From P of valve socket to P post. Operation. Remove aerial and earth from set and attach to booster. Attach lead from B battery 45 + to ground post on , set. Attach lead from plate post of booster to aerial lead on set.

PULTE UE LECCE UL COMPONENTS FOR BOOSTER; Variable Condenser .0005, Coil Made or Bought, Rheostat. Valve and Valve Base. 5 Terminals. 2 Pieces of 6ft. x 6ft. x fin. Timber. 1 Fixed Condenser ( 1 mfd.) 1 15 ohm. Resistance. Approximate Cost, £1 16s.