I recently uploaded a video to You Tube that discussed how the basic valves (Tubes) work. I have also produced a series of information sheets that i wanted to make available that build on the information in the video.
They can be downloaded using the links below. If you have any questions, please leave a comment on either here of the You Tube video.
Valve (Tube) tutorial Super Heterodyne Radio Receiver tutorial
http://www.grumpyoldtech.technology/attachment/Diode.pdf
http://www.grumpyoldtech.technology/attachment/Triode.pdf
http://www.grumpyoldtech.technology/attachment/Tetrode.pdf
http://www.grumpyoldtech.technology/attachment/Pentode.pdf