Oh knowledgeable ones here on the forum, I have a copy of the RCA manual (reprint 30) coming, but what would be a good source book on identifying tubes from various manufactures, eras etc. etc. When I hear ''double getter black plate'' I have a basic idea of what I'm looking for or at, but can you all recommend a ''bible'' for this adventure? I found a couple of boxes  of tubes from my days back in the audio business and some of the gear I used to own (MC-30's)  and it would be great to have some more info. Thanks, and Happy listening, Chris.