Laboratory Jottings

Radio Record, Volume V, Issue 19, 20 November 1931, Page 14

Laboratory Jottings

The G.M. Midget We have had the opportunity of testing a seven-valve General Motors Midget Super-heterodyne, and the following notes are based on that test. The appearance of the set in a general way resembles that of most superheterodynes in that it is very small and very compact. There are three controls, tuning, volume and tone. ‘The tuning dial operates a low ratio dial graduated in kilocycles. It is of the circular pattern, an aperture in the set revealing an inch or so of the dial. A ‘pointer: indicates the frequency to which the set is tuned. We found that: the frequencies indicated by the dial were within 5 per.cent. of the frequencies on which the stations were operating. In operating the set two things impressed us; in the first place the set was. remarkably quiet, the noise level being reduced to a degree reminiscent of the older and generally considered quieter receivers. This has been accomplished by careful filtering on the mains side of the power transformer. The second point was the unusual sensitivity (combined with the absence of noise). We noted a slight difference in the relative strengths of stations received on either énd of the dial. It appeared to us’ that, contrary to the usual, greater sensitivity was attained at the upper end of the dial. , A slightly greater. number than the usual overseas stations was tuned in. Many small Australians were put on the speaker as well as several of: the Japanese. It must be remembered. however, that a sensitivity test must be comparative only. In a different locality this set would undoubtedly bring in American and European stations when operated with a standard aerial and earth equipment. The selectivity of the set is all that cau be desired, our requirements being that under our own particular conditions a set should separate between 2YA, 2FC, and 4QG, and that, in doing so, it should not beat up any harmonics, Cross-modulation was entirely ibsent, and there were no artificial harmonics. The tone of the set was good. It ‘overed a wide range of frequencies, ul. grades of voice and music being 1s natural as we have heard on a set this description. The tone contro} gave a nicely-graded tone, and we found fhat when worked more toward the ‘ass end a most pleasing reproduction was obtained. The power output of the set was approximately 84 watts, and when slightly less than one watt is all that is necessary for the average room, it will be realised that the set works with a great reserve of power. The volume control is smooth and even, and satisfies our requirements--the toning down of 2YA without removing the aerial which comprises 120 feet erected at a height of 40 feet,