BE READY

Sun (Auckland), Volume IV, Issue 954, 23 April 1930, Page 9

BE READY

NOW IS THE TIME TO OVERHAUL YOUR SET IN READINESS FOR WINTER. I

IMPROVE RECEPTION

Partly because receiving conditions are superior to those of summer, and partly because there are fewer attractions away from home in the winter evenings, winter has always been regarded as the real broadcasting season. For the next six months receiving conditions will be at their; best. With “static” at a minimum, reception is already greatly improving, and the longer evenings make it possible for very fair programmes to*; be obtained from many of the Australian stations. To make the most of the winter receiving conditions, every broadcast receiver should be I given a general overhaul about this i time. REMOVE DUST Careful attention to cleanliness inside the receiver cabinet is far more important in winter than in summer, because the possibility of trouble from faulty insulation increases with the increased moisture content of the atmosphere. In particular, all traces of dust should be removed from the interior of the cabinet, and from off the tuning coils, and between the plates of valuable condensers. The presence of dust on these components nearly always causes trouble, because dust possesses to a marked degree the power of attracting moisture. This breaks down insulation, discharges batteries, introduces unpleasant noises in the loud speaker, and reduces signal strength. A vacuum cleaner is an invaluable aid in removing dust from components, especially if it he fitted with a “blower.” This will be found particularly useful in blowing dust from between condenser vanes. In the absence of a vacuum cleaner, a motor-car or bicycle pump is a good substitute. In most modern sets the tuning coils are treated with some moisture-proof substance. If this has been omitted, the present time is a good one to apply it. The set should be placed in a warm, dry room, and left there long enough for all traces of moisture to dry out of the insulation on the coil The coils should then he painted lightly with a varnish made either by dissolving a little shellac in methylated spirit or by dissolving slips of celluloid, such as old photograph negatives from which the photographic emulsion has previously been soaked in washing soda, in amyl acetate. In applying either of these varnishes care should be taken not to use more than is necessary to coat the coils. An excessive quantity of varnish will introduce losses in the coils which may appreciably affect the reception of weak signals. Care should be taken to see that the tuning condensers are running smoothly, and are operating without “backlash” on the controlling dials. If any irregularity of running is noticed, it can usually be corrected by adjustments to the condenser bearings, or to the controlling dial. It Is wise thoroughly to overhaul batteries before the beginning of the winter season. Most accumulators which have been in use for a year or more without overhaul should be washed out. To wash an accumulator battery, it must first be fully charged. The acid solution is then poured off into a clean jar, and replaced by distilled water. The battery is then rocked gently to and fro, and the distilled water is drained off. It will almost always be found to be heavily charged with a dull red powder, which has accumulated in the bottom of the battery as a result of the disintegration of the plates. The washing process should be repeated until the distilled water comes away from the battery free from this powder. The acid solution can then be replaced in the battery. Terminals should be well coated with vaseline before the accumulator is replaced in the set. High tension batteries of the dry cell block type should he carefully tested by a volt-meter to ensure that the pressure has not fallen excessively. It is generally agreed that these batteries have reached the end of their useful life when the pressure has fallen to twothirds of the original pressure of the battery. That is, the popular 45-volt block should be discarded when it fails to show more than 30 volts on test. Batteries of other pressures should be replaced when the voltage is correspondingly reduced. EXHAUSTED VALVES A fruitful source of unsatisfactory operation is the use of exhausted valves. The fact that the filament of a modern dull emitter valve will still light does not necessarily indicate that the valve is in good working order. The operation of the valve depends on the presence in the filament of certain substances possessing slightly radio-active properties, and the supply of this material is usually exhausted before the filament actually “burns out.” Valves should be replaced at least once a year, unless the receiver is very little used. A rough method of testing the valves is to allow them to burn for half an hour with the high-tension battery removed from the set. This enables the filament slightly to recuperate. If an improvement in operation is noticed when the high-tension battery is replaced, it can he assumed that the valves require replacement. In passing, it should be noted that the valves in a high-tension eliminator are subject to the same exhaustion as those in a receiver. Should the filament of these rectifier valves become exhausted, the eliminator output must fall off substantially. Signal strength, sensitivity, and tone quality will then be impaired. INSPECT SOCKETS General mechanical features of the receiver should also receive attention when the overhaul is being made. In particular, care should be taken to see that valves are seating effectively in sockets. Any form of looseness should be corrected, especially in sockets of the older type. This can best be done by removing the valve and, with batteries disconnected from the set, bending the spring contacts up with a pencil. or similar wooden implement. Slider arms of rheostats and potentiometers should be examined to ensure that they are making firm contact on the winding. Finally, tire aerial should be overhauled to make sure that joints are well soldered and uncorroded. It is wise in this process to replace cracked or broken insulators. The lead in insulator should receive special attention. Care should be taken to see that it has not been pulled out of place by the aerial so that rain water running down the lead-in wire can lodge in the insulating tube. Nuts, bolts and terminals throughout the set and aerial should be carefully examined, and when found to be loose should be tightened up.