ANSWERS TO CORRESPONDENTS

Radio Record, Volume I, Issue 16, 4 November 1927, Page 14

ANSWERS TO CORRESPONDENTS

BIVE-VALVE BROWNING-DRAKE. A. J. (Yaukei).-A five-tube Brown-ing-Drake is usually impedance or re-sistance-coupled in place of transformer coupling on the audio side. The former is recommended rather than the latter, Mr. Browning, the inventor of the circuit, in a recent article, recommends for impedance coupling the National impedaformers, otherwise a radio choke must be placed in series with the first choke coil and the .lmfd. fixed condenser. Adding an extra R.F. yalve is not a simple proposition if the valve is to give its quota of amplification. The ordinary one-radio circuit of four valves is wonderfully good when worked up to full efficiency by experimental improvement, Using Ammeter, R.G. (Mangonni), inquires regarding short-circuiting batteries. An am-_ meter must never be used on an accumulator on any account, as the construction of this instrument makes its use equivalent to a direct ‘‘short,"’ which is ruination to an accumulator. Even on dry batteries its use should be avoided. A voltmeter with plenty of fine wire on its coil may safely be used on any battery or accumulator. Care must always be taken in using these meters that the metal case is not allowed to touch the terminals and cause a "short." Adding Amplifier. A Nelson reader has been having good reception of small Australian stations on his two-valve set and wishes

to know why, on some nights, New Zealand stations come in well in speaker and other nights only ’phone strength. This is attributable to at: -mospheric conditions that are not at present very well understood. ‘There are nights when a multi-valve set only gets ’phone strength on main Australian stations, but this effect is seasonable, and most acute during summer time. Dunedin is a weak station at present, but will probably be on increased power at later date. ‘Ihe suggested addition of a one-vyalve amplifier would certainly increase volume, the increase depending to a good extent upon the transformer selected and the workmanship put into the circuit. A & to 1 ratio good-sized transformer {s recommended, fixed condenser across primary and across ’phones or speaker-value best found by experiment. A small power yalve would probably suit best. Charging A Battery Without Mains. A country reader states that particulars have been broadest on how to charge an A hattery accumulator by means of wet cclls, and asks for particulars of how to do this. ""Megohm?’ has no recollection of hearing this broadcast, but realises that such a Sys- | tein, which can be used, would be of | tremendous benefit to country listeners who are away trom electric mains. Briefly put, the accumulators are charged by means of Daniel cells, to Which they are permanently conuected, the Daniel cells acting as a trickle charger when the set is not in use. Lhe system is quite inexpensive to instal, and is reliable. To make the best of such a system it is wise to use four-volt valves rather than six-volt in order to economise current, but as the four-volt series give excellent results, there need be no hardship on this account. ‘Megohm’" has a good description of the system, and will endeavour to present it as fully as possible next week, with necessary diagrams, feeling sure that it will be much appreciated in isolated districts. The system is to charge small accumulators suited to their work, but does not lend itself to charging large capacity six-volt accumulators. Improving Browning-Drake, A Hunterville reader has a 4-valve Browning-Drake with 201A valves presumably all through), but is doubtfm as to having correct number of turns on coils, and is not satisfied with tone, although volume is there, The primary turns fo suit the 201A in radio Stage are generally 14. With .0005 variable condensers, 65 turns, spacewound for aerial and R.F. secondary

coils, ickler turns depend on efticient coustruction of set, the more efficiently built, the fewer turns required to secure oscillatién up to high wave-lengths. Good toue is obtained with a large 6 to 1 ratio transformer in first audio, and AF8 ITerranti in second stage. Across primary of first transformer a fixed condenser of fair capacity and another smaller across plate and grid terminals of same, exact values to be determined by trial for best results. Choke output filter, and condenser of good capacity across speaker terminals. The 201A in last stage must be replaced by a good power yalye, without which good tone and volume are impossible. A plentiful high-tension supply is also a necessity for good tone on the lower audio frequencies, or the sudden demands of a power valve are not met, and loss of volume and roundness is the result. A good speaker is, of course, another essential, Other information will be found in back numbers describing the circuit. Short-Wave Adapters. A request for particnlars of ‘how to counect a short-wave adapter to certain reflex sets will have attention. ‘