Book excerpt: Discover (or rediscover) the fun and magic of building electronic circuits with thermatrons (vacuum tubes). This book has everything you need to know about the art and science of thermatron design and construction. It pulls together, in one easy to read book, thermatron types and characteristics, thermatron homebrew techniques, and how to design audio and RF triode and pentode circuits. The book is written primarily for radio amateurs (or audio equipment builders) that already understands basic electronics but have forgotten or never had the pleasure of working with hollow-state devices. The Second Edition includes over 50+ pages of new and revised material including a new chapter on thermatron oscillator design.