This book explains how radio receivers work. the explanations have been set up as conversations between Weetal (Knowall), 18 years old and Vraagal (Askall, 14). Despite this format and the simple drawings by H. Guilac, the book covers subjects upto the superheterodyne (site). I have scanned the book and have made it available as a 64 Mbyte pdf.

The mysterious soft glow of radio tubes has always fascinated me.

Flow of electrons is like the emigration of Japanese because of the overpopulation of Japan (1939 !).

The basics of detection.

Amplifier pills of Dr. H.F. for weak currents.
Amplifier pills of Dr. H.F. Before use: cannot be rectified. After use: can be rectified.

Detection by use of an diode and triode tube, a combined diode-triode tube, and grid-detection in the triode tube.

The superheterodyne.