Notes From Far and Near

Press, Volume LXVI, Issue 19918, 3 May 1930, Page 10

Notes From Far and Near

To give some idea of ! the growth of tho demand for valves in the United States of America, ono manufacturer expected to increase his production from 10,000 to 24,000 valves, daily, in the course of six months. Unfilled orders were stated to be nearly two millions. Another tube company had £400,000 worth of unfilled orders, whilst the Ceco firm had one order totalling over £IOO,OOO.

One cause of faulty reception is a defective lightning arrester. Signals might be very weak or the background might be very noisy, rooro likely the former. Dirt or water getting into the arrester is the cause, so if reception seems bad and the receiver appears to be correct, do not omit to overhaul the arrester. Disconnecting it for the time being is the best way to test, but bo sure to seo that tho earth connexion from the set, if it joins tho unit, is not left open-circuited.

A service-man states that another curious trouble was traced to a pilot light in tho panel, and a poor rattling connexion was the culprit, vibration of the loud-speaker causing the light to make intermittent varying contact and upsetting the music.

Tho 227 typo of valve is also often an offender, sometimes developing sounds in the speaker which resemble snores. This fault is duo to filament flicker, want of sufficient support being tho trouble. Changing for a faultless tube is the cure, the offender generally being in . tho detector socket.

Brand new dry "B" batteries should give 46-48 volts, but it is very unlikely that wo can secure such specimens: in this country. A high resistance voltmeter would be required, but a medium lesistanco one is a bettor one for aver-age-testing, as if the life of the battery has dropped only a little, it might give suflicient current to show a good reading, whereas a lower .resistance meter taking- more current, would show a lower voltage and ono moro indicative of the real condition of tho battery. The writer has known a completely rundown "A" battery to give a reading of six volts with a high resistance'meter after it had had a short rest, residual electrical energy being responsible.

There are several systems in use for ships approaching land whent a radio directional bearing is wanted. For ship-to-ship work, in fog or when close to land,, both an audible sound and • a radio signal are dispatched. The former travels at the rate of about 1100 feet per second, whilst the latter is instantaneous. The time difference in seconds, multiplied bv 1100, gives the distance in feet from tho indicating beacon.

One of the simplest, and one which is useful for a ship some distance from the shore, is to obtain directional bearings from two different radio stations which are equipped with directional apparatus. These are plotted on tho chart and give the correct position of the ship.

A third method combines two signals sent on two different wavelengths, simultaneously. Tho signal from the shorter wave is stronger at distances greater than 3000 metres, and tho longer wave predominates at shorter disiancos, whilst in tho vicinity of 3000 metres the signals combino to produce dashes only.

Vessels themselves sometimes carry direction-finding apparatus, and take their own bearings, when wanted, of different radio- beacon signals, and so determine for themselves their position. The latest regulations for commercial wireless operators' tickets show that part of the examination now covers the use of direction-finding apparatus. In fact, tbo sea-going wireless man haq quite a stiff examination to pass these days, and rightly so, for reasons that are obvious.

■ Arrangements have now beon completed for the transmission of messages of greetings from the Dunedin Eadio Exhibition, held this week, to different parts of New Zealand, via amateur radio stations. Tho number already transmitted to Christchurch is over double that of last year.

"Whon a soldering iron has to be heated in a firo it is a good plan to 'place an empty tin on the firo, the end of the iron into this so that it is heated without coming into actual contact with the dirty ash.

Soldering a pigtail connexion between the spindle and the appropriate terminal of a variable condenser which depends upon pressure contact to the moving vanes will often improve efficiency greatly.

A reader points out a curious trouble which ho has experienced which proved to be very difficult to locate, and asks mo to give the information in these Notes in case it may ,be useful to others. lie finds that when working with a set using S.G. amplification, the condenser between the filament and the screen grid must be connected to the negative end of the filament the same as the other condensers; It appealed to me to be fairly obvious that oscillation trouble might be set up. Of course, the bypass condensers in the set should be connected to the same end of the filament.

When fitting a potentiometer to improve control, remember that its action must ,bo smooth and reliable, or it ■will cause far more trouble than.it is worth.

Yery often a short-wave set works better without the earth connexion.

In many cdses a fair amount of the trouble experienced with regard to paiasitic noises in radio reception may be directly traced to the faulty installation of loud-speaker lines. It must be remembered that good 'contact from an electrical point of view is not necessarily good contact from a "wireless" aspect, and a little care in laying loudspeaker extensions will always pay.

In the first place, it is not . a good plan to use twisted wire for extensions, as this has rather great salf-capacity, and can quite easily give rise to an unpleasant hum, especially if light or power mains .are to be .found in the immediate vicinity. ' * * The wire used should be of a wellcovered, single type, and should naturally be of different colours, in order to distinguish the positive and negative of the loud speaker and output of the sot itself. ' r As to the question of whether wires should be fixed away from the walls, this is not really important, unless the wire runs tHrough * a kitchen or some aimilar plaee wier# -there ii likely'tfi

(BY "MAX.")

b- a considerable quantity of steam or moisture. There is a twin wire now made bv a certain firm which is m every way admirable for this kind of extension work. , It consists of two (or three) wires, untwisted, and held together by a material something like webbing, which can be obtained in a great , variety of colours. Incidentally, special fastening pins are supplied with this wire, which do not damage the walls —a very important consideration when there is the possibility that the extension may at some time have to be moved.

* * . - There are just two more points which should be noted. First, run the wires as near the ceiling as possible, because for one thing, they are less noticeable, and for another they are out of harm's way. i

Lastly, do not run them parallel to or near electric-light or power lines, for if you do you may get a very noticeable and annoying "ripple," the only cure for which is to move the extension or place a large fised condenser across the L.S. output terminals, both of which courses mean trouble which would have been rendered unnecessary by a little more: ears ia the first place.