Questions and Answers

Radio Record, Volume III, Issue 54, 25 July 1930, Page 29

Questions and Answers

" B." (Umawera) has a six-valve | ’* battery set and complains that one of the valves had tape round it when | it was bought, and asks if this will interefe with its performance. A.: Probably the valve is only a little loose in its socket. It will not | be impaired because of the tape. 2. Of the six valves four light and two do not-are these valves exhausted? ; A.: No, they have an inside covering of mercury which preyents any glow from being visible. 3>-HAclosed is a diagram. Are the valves correct? A.: Interchange Nos. 1 and 5. 4, Can I substitute one of the valves with a screen grid? \s A,:,No, a special circuit is needed for the screen grid valve, 5. Only one "B" battery, one "C" battery, and one accumulator 100 volts was sent with the set. Would there be y any improvement by using more "B" ‘batteries? A.: Your specificaitons are confusing. The accumulator you refer to is probably a 6 volt 100 amp.’ hour capacity If it is a 100 volt "B" accumulator and used in series with the bat_tery, then you have ample voltage. If you have only 45 volts "B,"’ you will require at least two more batteries and take tappings for the various valves, | as shown on the battery diagram which accompanies the set. "RN B.T." (Palmerston North) asks if | a 2-amp, "A" and "B" battery charged can be converted into an eliminator? | A.: Probably the transformer of the "BY" battery can be employed in an eliminator. It depends if it will sup- | ply sufficient current at a high enough voltage for your requirements. You will need a separate rectifier, which for a small set may be an ordinary power valve. The "A" part of the equipment can be used in conjunction with a stiitable choke and condenser as an "A" battery eliminator. A suitable arrangement has been described in this year’s Guide.

"H P." (Wellington) has a Cossor *Melody Maker, and wishes to enlarge the set with an extra valve. What others parts would be required? A.: You will need a transformer, a valve, andj a valve base, and either an output jack or two terminals.’ . 2. Cen I put this in the set? A.: There would probably not be room. You would possibly spoil the layout. You could make a neat little

attachment that would not look. conspicuous. 8. When I tune in distant stations there is a loud howl, but when I put my hand on the it cannot be heard, A.: Is the set earthed propetly? Have you tried connécting your earth to the cabinet as well as to the usual terminal? Has the noise always been there? If not, what caused it? You see, you are not giving us quite enough information. "RR P.I." (Lyttelton) is intending to * construct the "B" accumulator described in the 1930 Guide. He wants to know if a car generator driven by a petrol engine can be used. A.: Yes. Arrange the tubes in series, parallel, so that the voltage of those in series will be equal to the voltage delivered by the generator. Put resistance in series until the charging rate is down to about 60 milliamps. 2. How long would be required for a weekly charge? A.: This depends on how long you use it, and what the capacity of your set is. If the charging rate is about double the consumption you will need to charge about the same number of hours the set is in use. "M. H.M." (Ohristchureh) asks if 4volt A.C. valves are recoramended in preference to 1.5, 2.5 and 1-volt valves. A.: 1.5 volt valves are very little used now, but 2.5 and 5 volt are equally as good as 4-volt. R.A." (Auckland) asks where * porous pots for Daniells’ cells might be obtained. A.: We do not know of anywhere except the Telegraph Division of the Post and Telegraph Department. Unfortunately they seem plentiful in some places and rare in others. There are no substitutes, although possibly an electrician might be able to supply a few used pots. 2. What is the number of the "Radio Record" in which the article by "HardUp" appeared? A.: June 6, 1930.

"M H.M." (Christchurch) submits a * diagram of a 4-valve A.C. B.D., and wishes to know how to add the extra stage. We have returned his diagram suitably inscribed. 2. Can the Hammarlund-Roberts coils now in use be utilised in this circuit ?-Yes. 3. What other coils will I require in adding the extra R.F. valve? A.: An R.F. transformer, a duplication of the aerial coil without the tapPings, in the case of the H.R. In the case of the B.D. coils it is a duplication of the regenaformer without the tickler. 4. What is the output and voltage of 8002. eliminator? A.: Maximum 150 volts 30 milliamps. 5. Could this eliminator combined with a filament transformer successfully work a dynamic cone speaker? A.: That depends on the amplifier you intend to use. It could operate a single medium power valve or even two smaller power valves in push pull,