For years, author Rudolf Moers searched for a textbook about electron tube amplifiers in order to learn how to design amplifiers using electron tubes, given that one has a reasonable knowledge of analog electronics. Since he never found such a book, he has written one himself in a style and content such as he would like to buy. To achieve this, he studied many radio books and did many measurements. This was followed by the organization of all the information, making many drawings and calculations and a lot of writing. By all this effort, a lot of knowledge about electron tube electronics, which was under the threat of being lost, will be retained. There are two aspects of a technical book that readers like to see, but which are often poorly presented. These two aspects are accuracy and a pleasing readability. Readers less skilled in mathematics and interested only in formulae that provide a valid 'recipe' like to skip the derivation of that 'recipe'. In this book this is possible without prejudice to the readability of the story. These 'recipes' are framed at the end of formulae derivations. There are readers who are not satisfied with formulae that 'fall from the sky' without derivation. For these readers, a 'recipe' without substantiation is unsatisfactory and the application of the formulae will be accepted only when the derivation is shown. The formulae are proved in such a way that the reader can easily follow them through, thus a deep knowledge of mathematics is not necessary. The introduction in chapter 1 will be followed in chapter 2 by the principles of electron emission. Chapters 3, 4, 5 and 6 treat the diode, triode, tetrode and pentode respectively, each with a different framework, but only at middle frequencies and without discussing distortion and negative feedback. Chapter 7 treats the limits of audio frequencies and in chapter 8 are discussions about distortion and noise. Chapter 9 concerns negative feedback and in chapter 10 you can read how to build your own electron tube amplifier. Much of the theory is checked against practice, and design methods give the reader help to start with the design and construction of electron tubes amplifiers. The aim of the book is to give the reader useful knowledge about electron tube technology in the application of audio amplifiers, including their power supplies, for the design and DIY construction of these electron tube amplifiers. This is much more than just building an electron tube amplifier from a schematic made from the design from someone else: not only academic theory for scientific evidence, but also a theoretical explanation of how the practice works. No modern simulations, but because you first understand the circuit calculations, then you can work with your hands to build the circuit and last, but not least, if you have a multimeter, a signal generator and an oscilloscope, you can measure the circuit parameters yourself to see that theory and practice are very close. That is the aim, and makes this book a unique reference source.