Laboratory Jottings

Radio Record, Volume III, Issue 21, 6 December 1929, Page 30

Laboratory Jottings

Components .and Portables HE following coniponents, supplied by A. Hi. Striu ge, electrical -engineer, Christchurch, have been tested to. our satisfaction : — Dubilier 0001 Variable Condenser. This piece of apparatus has been specially designed for short-wave work. It has.a special ball-bearing gear which enables a fine adjustment. The ratio of the dial movement to condenser movyemert is approximately 200 to 1. A rotating shaft moves a bushing piece at the back of the condenser and. between this and the shaft is a single glass ball-bearing which moves its position as the dial is rotated. Thus perfectly smooth movements may be obtained and‘ the finest values of capacities are possible. This condenser is particularly suitable to short-wave work. The .0001 midget variable condenser has also been supplied for tests. This is of the usual type for balancing and may be used for reaction. Horizontal Grid Leak Holder. ° This Dubilier product, which is sturdily made; may be fitted into any

its manufacture, with the result that it will stand up to hard work in the form of pulling about from one circuit to another. The vertical grid _leak holder has its application in the circuit where the grid of the yalve is connected to A -+ for detection purposes. The grid leak tested was _perteetly silent -and satisfactory. . ; : \ set. is nothing shoddy. ubout / -35. Ohm Resistances. This is a fixed resistance similar to the Amperites; and, mounted as they are, its application in the set is where the voltage of the valve is much lower than the voltage of.the accumulator. The Airzone Portable, OTHING is more useful in providing musie during camping and pc nic. excursions than a good porte and our test of the "Airzone" (Sm and Co.) reveal that it is one of the best. Tested under adverse conditions, heavy static and bad _ localities, this set performed well. It always brought in 2YA even at great distances, and when a temporary aerial was. erected it was as good as a home receiver. The circuit is the familiar BrowningDrake, with the antenna coil enlarged as a loop antenna, in which a tap for an aerial is provided. The ground joins the filament negative through a terminal in the lid. An automatic switch is provided by which the set ‘is shut off when the lid is closed. Battery currént cannot thus be wasted by the set being closed up with the rheostat on. Everything is robust, and will stand reasonably rough handling. The builtin speaker is exceptionally good for this’ class: of work, and is a pleasure to listen to.