WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Any edition of the RCA Receiving Tube Manual will have an exploded view of tube internals, various editions can be found on Pete Millet's site - he has done a terrific job of putting up pdf copies of many tube related technical books and manuals: Tube Data