Tips and Jottings

Radio Record, Volume II, Issue 6, 24 August 1928, Page 28

Tips and Jottings

Short-Wave Tuning. LISTENERS who find difficulty in tuning their short-wave sets can make matters easier by using a dial of higher ratio than that at present in use. A variable condenser of .0001 capacity is often used to facilitate tuning, but if substituted for one of larger capacity would alter the number of turns required on tuning-coils, and would also necessitate an extra coil or two. Audio Volume Controi. ONTROL of volume by means of a variable resistance across the

speaker leads or any part of the audio system is very unsuitable for a receiver capable of giving good volume. if signals inerease, the detector is overloaded, and distortion occurs, and no amount of reduction by shunting the sudio output will remedy matters. The R.I. filaments are the only ones to use for volume control, and they should not be dimmed too near the point where distortion begins. Request for Reflex Circuit. A CORRESPONDENT sends in a request for articles on the crystalreflex type of receiver. As a general rule this type of circuit is not a success for home construction, and was developed when valves were £2 each, on the score of economy. Greater satisfaction will be gained by commencing with a couple of valves than with one valve and a crystal. "Improving" Factory-built Set. A CORRESPONDENT signing himself ‘"Distance-getting," has a six-valve set with six 201A’s in the sockets, and asks how reception can be improved. A power-valve could be placed in the last audio stage, a B605 being recommended for this particular set. The radio frequency valves should be kept as at present, as a different type of valve requires .jeneutralisation of the receiver. Many factory-built sets can be improved by. adding a power-valve and also by putting in better audio. transformers, but beyond this it is just as well for the average listener to let well alone. .:

Charger Transformers. WHEN making transformers "f ¢ Uj battery charging purposes essential point is the tight packing of '. laminations. Any looseness will ake itself heard by an_ objectior*®ble "rattle"? or rough hum, which "way ‘cause a suspicion that something more serious is amiss. A liberal coating of shellac on the laminations fulfils two ‘useful purposes: firstly, the prevention of eddy currents in the core, and secondly the deadening of mechanical rattle. Correct arrangement of the clamps and tightening screws will do the rest, provided the laminations are carefully packed tight inside the spool containing the windings. Tinfoil Fuses. , A CORRESPONDENT who has used tinfoil fuses for some time calls attention to the fact that some cigar ettes are packed in foil that is not suitabie for fuses. The sample enclosed is of a hard, "rattly" type, resembling aluminium, with embossed striped pat‘tern. Constructors making this type of fuse should see that they use the soft, or real tin or lead type of foil.

Indexing Constructional Articles. AS goon as time pe:imits, an index to the main constructional articles, etc., will be printed in the "Record" to facilitate looking up back numbers. A Useful Catalogue. THROM Wiseman's, Limited, Auckland, a well-printed catalogue has been received. The well-known AtwaterKent receivers are listed and described. A description of the New Zealandbuilt "Courier" sets deals with receivers from one valve up, including a 4-valve high and low wave. A gewéral list of components, eliminatots, chargers and sundries completes the catalogue, which intending purchasers would do well to obtain.

B Battery Resistance. AN old, run-down 80-volt: B battery may have an internal d.c. resistance of over 1000 ohms compared to 4 ohms for a new battery. No wonder an old batter) can cause unsatisfactory reception. The d.c. resistance of a B accumulator is almost negligible, though the a.c. resistance may not necessarily be so. The advantage is that it remains fairly constant. Noisy Reception. [TF reception is marred by crackles and noise, and the set is suspected, disconnect the aerial, and if the noises are still present, the receiver is the culprit. To test for faulty connections or loose joints, pound the table with the fist, ightly, and listen. Ii the noise is affected, carefully touch arounc the internal wiring points, aAvobble the valves in their sockets, , listening all the time. This will locate bad connections. Clean valve legs with glass-paper occasionally. If the trouble is not located, it may be caused b: the batteries, broken-down audio transformer winding, or numerous other things. Insulated Wire Supplies. YT ARGH stocks of insulated wire }for "" yadio and electrical nurposes aye earri7d by the Lawrence and Hansén Electrical Co. Ltd. 85 Lower Cuba Street. Wellington. The firm also specialise, in the well-known Scerling ‘Joudspeakers several patterns, including the popular "Baby Sterling.’