"Understanding Radio", by Watson, Welch, and Eby. McGraw-Hill 1951.
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"This book is written for students who have little or no background in
electricity or science".
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This book starts out its coverage of "glowbugs" by smashing one open and
examining the grid, plate, etc!
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It then proceeds thru a series of circuits, starting with the crystal
set, vacuum tube diode detector, triode, etc. The 1H4G is used for many
of the early circuits. Each project has a "why-it-works" section. To
give you a feel for the level of detail, the discussion of the Hartley
oscillator takes 15 pages.
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  -bill ab4yd