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Radio Record, Volume I, Issue 19, 25 November 1927, Page 4

The special detector (Q0U.\ type) valve is one of extreme interest, and takes a certain amount of understanding, but it amply repays the owner for a few moments of thought and reading. Generally. most special detectors are filled with an inert gas, and take a few moments to "warm np’? to themselves, so to speak. But when they do, oh, the difference in reception,