TIPS AND JOTTINGS

Radio Record, Volume I, Issue 43, 11 May 1928, Page 13

TIPS AND JOTTINGS

A CONSTRUCTOR | at: Spreydon, Christchurch, writes as follows: "I have just completed the construction of the full-wave B battery eliminator that you gave in the ‘Radio Record" some time back. Although I have been some time building this eliminator on account of delays in procuring parts, I must say I have been amplv rewarded for the trouble, or, I should say, the pleasure it has give. me in the making. ‘The eliminator has prov ed a great success. I have not been able to detect any hum, and have far better results than formerly. Words cannot expréss my appreciation ot this design, and manv others that you print in the ‘Radio Record.’ "’ Short-wave Adapter, She long as only limited waveband of reception is satisfactory to the listener, one set of fixed coils is quite a good idea, but to be able to cover the entire range the plugin coils are worth while. A .00N25 variable condenser answers quite well for secondary control, but the use of a condenser of smaller capacity makes the necessary fine tuning much easier, and is invaluable in a receiver that may at any time be recuired to get down below twenty metres, where the {frequencies are tremendously high, and tuning consquentiy more difficult. Neutralising the Browning-Drake, QU VERAS, inquiries have comie to hand regarding neutralisation. ‘The early part of the instructions in recent specifications was rendered ambiguous owing to the printers misplacing a line, so we give the instructions here. ‘Tune in a loud station near centre of broadcast waveband, 1YA or 8YA, maximum volume being carefuily obtained without oscillation, reaction being turned well down. Next turn out the filament of REF. valve, then with the neutralising stick turn neutralising condenser until signals are inaudible or at minimum strength, then turn on filament of R.F. valve, and the station should

come thiough well. Now see that the variable condensers are both at maximum twiuing; if not, they must he altered to get the Lest tuning, and the process of neutralisation is gone through again. ‘The second attempt is practically certain to be correct. If neutralisation cannot be obtained, reverse the connections to the R.I. primary and try again. If it cannot be obtained either way, it may be an indication that the cspacity of the neutralising condenser is too great or too small, fn either case the correct value must be substituted. Rectifier Tubes. FOWO new Radiotron rectifier tnbcs are the UN2s80 (full wave) and UN281 (half wave). These contain a new trpe of oxide coated ribbon filament giving high emission with low power input. The filament of the former takcs 5 volts at 2 amps. and the maximum output is 125 milliamps at 800 volts Yhe half-wave tube — reauires 7.5 volts at 1.25 amps on the filament, and passcs 119 milliamps at 750 volts. Alternating Current Receivers, UIT, a large number of these reeeivers has now been installed in listeners? homes in New Zealand. The distributors state there has been far less trouble in every way with these receivers than with the average battery set, and that all are working satisfactorily. Be Careful of UX222. ARE must be taken that when in action the UXY22 dces not receive a shock, which may cause the filament to tonch the control grid and burn out. Purchasers of these valves should test them with a 6-volt battery, one pole being connected to a filament pin, and the other touched on each of the pins in turn. ‘The filament should only lieht when battery leads are both on the filament pins. If there is a circuit in any other way, the valve is defective. Test also for connection between inner screen and control grid, and between plate and screen. Big B Batteries Pay. T pays best to purchase the large sizes of B hatteries, where several yalves are in use, for as a rule the battery of double milling ampere capacity will last more than twice the time of the smaller one on the same work, as the larger the battery the less will the strain of a given demand be felt. The Browniug-Drake Primary. In constructing the R.F. transformer for the Browning-Drake, care should be taken to provide good insulation between the primary and _ secondary coils, owing to the high potential difference across them. In no case should the insulated wires of one be allowed to come into contact with those of the other, but the insertion of a strip of stout paper between the two will remove any chance of a ‘‘short.’’

QUERIES BY CORRESPONDENCE. 1. Every communication enclosing queries is to be addressed to "Meg: ohm,’’ Box 1032, Wellington, and must be accompanied by a stamped address: ed envelope for reply by post. 2. Questions must be written so that a space is left in which the reply may be added. 3. No charge is made for replies. AEE EEE EEE EE