One of the many great things about the SF Bay area is that the Burning Amp festival is held here each year. In addition to Nelson Pass, this years guest speakers also included Roger Modjeski from Music Reference/RAM Tubes and Wayne Colburn from Pass Labs. Sadly though, Siegfried Linkwitz's presence was greatly missed (but there were some touching tributes, including one from Nelson Pass), but his room still provided great enjoyment for the attendees. While there were many great projects to be seen, the real pleasure is listening to the lectures. For those interested here is the link to all the videos:http://www.linearsystems.com/burningamp.html
If you would like a primer on tubes Roger's talk discusses various types of tubes in detail. In particular, at one point he even discusses how he designed the RM-10 amplifier to put out twice as much power compared to other circuit designs, old and new. I've known Roger for quite some time and I cannot recall ever hearing him discuss the specifics as he does in this talk.
For those interested in adding 2nd order harmonic distortion to your system, Nelson's talk discusses his new toy, the H2 Harmonic Generator. While this was developed as a kit available on DIY Audio, working boards were distributed at the show. Nelson's analog crossover for the Linkwitz speakers was also part of his talk and again made available as a finished board for attendees. The man's generosity to the audio community knows no boundaries.