Tips and Jottings

Radio Record, Volume II, Issue 14, 19 October 1928, Page 28

Tips and Jottings

Variable Condenser Capacities. T is impossible to apply any yule of counting plates to give tae capacity of any variable condenser, as the spacing between plates is a governing factor-reduced spacing gives increased capacity. There is, however, 2 standard spacing that is used at the present time in most factory-made condensers, so that the following total number of plates will give a fair indieation of the capacity :-About 23 plates, .0005; 17 plates, 00085; 11 plates, .00025; 5 plates, .0001. These figures refer to the Hammarlund and other makes of condensers. X-ray Valves. ie is not perhaps very generally known that Philips Lamps, Ltd., do a large business in X-ray valves in addition to the rapidly-growing volume of radio products. Business in the latter especially is increasing by leaps and bounds, necessitating two extensive increases in office and ware: house accommodation at the Welling: ton house during the past few months A low-powered experimental shortwave station is to be erected in Wellington in order to conduct the tests in co-operation with headquarters at the other side of the globe.

Speaker Cut Out by Telephone. WHERE the loud-speaker and tele phone are situated together it i: necessary to stop the speaker whils' the telephone is being used. As the telephone instrument may not be tam pered with in any way, this cut-ou may not be made automatic, but th next best thing is to break one ofPth speaker leads, run an extension . wir from each side of the break up to thi telephone, where a small switch is in gerted between the two leads ant screwed to the wall. Anybody usin: the ’phone can then cenvenientl; switch off during the conversation loud-speakers in other rooms continu ing without interruption. Built-in Loud Speakers. {t is quite an easy matter to buil a loud-speaker into a eabinet be low the receiver, and it has often bee! done quite successfully as regards re ception. But it is a wise precautio! to first know the capabilities of th receiver with regard to microphoni susceptibility. A receiver fitted wt! microphonie valves might give endles trouble when built above a loud speaker, and for this reason exper! ments should be first conducted to dé termine the suitability of the outfit fo such arrangement. The Double-Roll Speaker. N Otago constructor says :-"I hav constructed the double-roll speal er and have had it running for week, and its reproduction of both hig! and low notes, together with its sens tivity to weak signals; has been revelation ; it is certainly all yo claimed for it and more. It. easil outclasses both of the horn speaker I have here. It was made exaetly t your specifications, purchasing th proper cone paper and an omniphon unit, Re