The "Rotorua" Portable

Radio Record, Volume II, Issue 24, 28 December 1928, Page 28

The "Rotorua" Portable

Operating Hints

A MISTAKE was made in the number of turns tientioned for the construction of the frame aerial. It was stated that 20 turns centre tapped should be put on. This should have read 10 turns centre tapped and spaced tin, . The Speaker Unit. 1 a number of speaker units the magnet, projects about 3-8in, over the front, thus preventing it being screwed directly on the baffle. If a piece of wood 8in. square and #in. thick is fastened at the*back of the silk b.hind the speaker quill, and a hole cut of sufficient size to allow the flange to be screwed on, the projecting magnet will have room between the cone and the silk. If the constructor has a speaker unit that will not screw directly to the front baffle he will understand what is meant, B Detector Voltage. AS the detector valve is fed through a resistance in its plate lead, the detector B voltage will have to be slightly more than with the usual transformer coupled detector. . As much as 674 volts may be required to get the detector to oscillate nicely, Always give as much grid bias to the last valve as possible, as this decreases the drain on the small B batteries, Working from Car Accumulator. [* the constructor is touring the country in a car, the filament current can be quite easily obtained from the car battery, instead of using dry cells. The valves will, however,

4 have to be of the six-volt type. Lead the filament wires to two terniifals on the front panel, and fasten to these a length of twin flex, on the end of which is attached an adaptor for plugging into the dash or dome light socket of the car, If this method is used, try the adaptor both ways round to determine whether the A battery is connected correctly. No result, or distorted music, will occur if the A battery is connected wroigly. Some cars have the dash light in series with the tail’ or rear light, in which case this plug is unsuitable and the dome light will have to be brought into use, . Results Obtained. A THEW results obtained by "Pentode"’ may be of interest to constructors, Using the outside aerial in a position twelve miles from Wellington, all the New Zealand and five Australian stations tuned in on the speaker. Using the frame above, 2VYA is loud gramophone strength anywhere, whether in an iron shed or on the beach. 8YA, 175 miles distant, good ’phone strength. 1YA, 400 miles, just audible.