The late Dr Christensen is an amazing teacher and human being. His insightful academic expertise coupled with his extraordinary ability to communicate has made him a superb professor and teacher. I have watched a number of his presentations on KZfaq and have been so impressed with his capacity to express complex concepts clearly along with his wonderful humility and humanity. I have read his book, The Innovator's Dilemma, and will read it again, now having the benefit of his KZfaq presentations.

Such a great talk!

Actually vacuum tubes have since made a small come-back. The music amplifiers enthusiasts love them. And they use vacuum tubes in high-end amplifiers.

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