Trade Developments
The Dongan Power Unit
BEL SMEETON, LID., Auckland, have submitted to us for test and report the Dongan power unit, a transformer to step down the voltage from the 220 mains to simplify the building up of an eliminator. The unit is enclosed in a small metal case, the over-all dimensions of which are approximately 6 x 4x 4. This is finished in crystalline. It is made in two distinct types suitable for filament and filamentless rectifying valves. The latter type has been tested, and the following remarks apply to it:-The condensers, resistances, and valve were easily procured and assembled. A Raytheon BH was used as rectifier. Full instructions accompany the unit, but the following are additions that have been found. advisable. As the power valve supply is taken direct from the rectifying valve without an intervening resistance a clarostat in series with this lead is suggested, as the voltage delivered is too high for the ordinary valve. Again, a clarostat in series, instead of in parallel, with the clarostat used for the audio tapping, is preferable for detector supply. Highgrade components only should be used in the assembly of the eliminator, as very high voltage has to be handled. The unit being assembled was submitted to test under load. The rectified TT SS
voltage before passing through any resistances was found to be 250. Passing through the first clarostat, the current was dropped to 80 volts. Thus this tapping was able to deliver anything between 250 and 80 volts, according to the adjustment. With this set at 175, a detector range of from 20 to 175 volts was obtained. With a semi-power valve in the Cir- . cuit, it was found that the unit was capable of delivering 40 milliamps. at 250 volts, though this cannot be claimed as its limitation; rather it was the limitation of the valve. There is an adjustable grid bias tapping which supplies negative voltage to the power valve. In addition to the rectified current, there are three other tappings on the transformer, 5 volts, 24 volts, and 14 volts A.C. This enables the owner to operate an all-electric set or to use the unit with a battery set, but derive the filament current for his power valve from the 5 volts A.C. A test under these conditians was made, that is, with A.C. on a D.C. power valve. It was found that the unit was very quiet and efficient. When the filaments of the valves were D.C. heated there was an absence of hum, though a slight trace was present when A.C. passed through the power valve, though this was not strong enough to be distracting. a EE ey eee
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https://paperspast.natlib.govt.nz/periodicals/RADREC19290419.2.65
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Radio Record, Volume II, Issue 40, 19 April 1929, Page 31
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448Trade Developments Radio Record, Volume II, Issue 40, 19 April 1929, Page 31
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