Laboratory Jottings

Radio Record, Volume V, Issue 42, 29 April 1932, Page 22

Laboratory Jottings

New Osram Valves HE British General Hlectrie Gompany, Ltd., has introduced two more American replacement valves. These are the 235, the variable-mu, and the 247, the power pentode, thus bringing up to date their list of American replacements. They have now a complete series covering all valves likely t» be required in a modern American set. These two valves were tested by our laboratory, the 285 mainly to see if it would fill the dual purpose of a 551 and 235 variable-mu calves, as was claimed by the manufacturers. Comparing the Osram 285 with the standard 285, we. notice little difference in characteristics, and it was thus to be expected that the valves could be interchanged without any noticeable difference in the output. This was the case. . In the case of the 551 socket, desisfhed for a valve which is really y ry little different to the 235, the replacement could likewise be made without ‘any detriment to either quality or volume, Whilst in our hands the yalye was soundly thrashed by subjecting it to vvyerload and rough handling, but it emerged after each test without showing any alteration in characteristic. It, together with a pentode, was worked in an American set for several months, then tested together with the other American valves in the set, and it measured up to all requirements, The new Osram pentode also embodies double mica bonding, which not only ensures great strength and durability, but minimises microphonie noises. The new yalves have been produced by the Osram Valve Works after extensive experiments on the part of the Research Laboratory of the G.F.C., London, and in producing them they have completed their range of American replacement. series. On conclusion we might remark that, so far us our tests haye gone, the valves haye proyed themselyes to be equal in all respects to our American standards, and: ¢an be classed as firstgrade yalves.