I think maybe the 3A5 is unique in the separate filaments. The 12xyz tubes have the one filament heat both cathodes, isn't that right ? 

The QST article, maybe 1940, used a triode - pentode. Of course, the pentode section becomes the receiver. 

This makes me remember a Hallicrafters novice radio where the ? 35L6 ? switched from audio out to crystal oscillator. Also the "Mighty Mite" another beginner set with a dual use ? 35L6? output tube. I have only heard of one Mite existing. 

-Hue Miller