06-05-2013, 11:28 PM
There is some legitimate technical basis for using a triode as a mixer. In general, the lower the number of grids in a tube, the lower the internally generated noise, called partition noise.
RCA did some research in the late 30's and found that multigrid tubes like hexodes and pentagrid tubes were the noisiest, followed by pentodes, and triodes being the quietest. So using a triode as the converter results in the lowest internally generated noise level. It is interesting that while RCA did the research, Philco actually put it into practice in their 1940's sets.
As to the XXL name, it seems that it was pure marketing. This way
Philco could claim that they were the only one using this particular "special" tube. Anyone could use a 7A4, but no one else had the "XXL".
http://www.radiomuseum.org/forumdata/use...e_TEXT.pdf
RCA did some research in the late 30's and found that multigrid tubes like hexodes and pentagrid tubes were the noisiest, followed by pentodes, and triodes being the quietest. So using a triode as the converter results in the lowest internally generated noise level. It is interesting that while RCA did the research, Philco actually put it into practice in their 1940's sets.
As to the XXL name, it seems that it was pure marketing. This way
Philco could claim that they were the only one using this particular "special" tube. Anyone could use a 7A4, but no one else had the "XXL".
http://www.radiomuseum.org/forumdata/use...e_TEXT.pdf
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