Guide to Vacuum Tube Amplifier Design

This free guide discusses all relevant aspects for an integrated push-pull vacuum tube amplifier design, including the power supply unit.

To clarify the various concepts,  I propose many practical examples using EL34, EL84, and 12AX7 vacuum tubes, to design the various parts of the circuits and to compute the values of the needed components.

Furthermore, the guide also contains a step by step design of an integrated push-pull vacuum tube amplifier, using EL84 power tubes, leveraging on all the notions introduced.

If you prefer to immediately start reading the full text for free, you can directly jump to the summary of content. Elsewhere, please find below an overview of what is in the guide.

Structure of the guide:

First of all, after an introduction to the guide, the basic principles to understand vacuum tubes are discussed. Certainly, this is needed by the non-initiated. However, If you already know what vacuum tubes are and how they operate, you can skip this part.

Then, the guide discusses how vacuum tubes can be used as amplifiers. Most notably, here, you will learn the concepts of operating conditions, loadlines, biasing techniques, and amplifier classes.

Continuing, the guide discusses how to design an integrated push-pull vacuum tube amplifier. To do so, it starts from the single-ended configuration, then it introduces the push-pull configuration. Consequently, the various needed stages (power, phase-split, and input stages), and global negative feedback are discussed in details.

A significant part of the guide is also dedicated to the power supply unit design for a vacuum tube amplifier. First, it introduces the rectifier configurations and filters to reduce voltage ripple, and to have a quiet amplifier. Then, it explains how to estimate the expected output DC voltage, ripple, and the current delivered. Furthermore, it also discusses how to design the power supplies for the fixed bias circuit and for the filaments of the vacuum tubes.

Finally, the guide goes through a step by step design of an integrated push-pull amplifier with EL84 vacuum tubes in ultralinear configuration. In this project, input and concertina stages, based on 12AX7 tubes, are directly coupled. First, the guide discusses the design of the power stage, the phase-split, and the input stage. Then, it discusses the design of the global negative feedback loop. Finally, it also provides the design of the corresponding power supply unit.

Summary of content:

You can browse and read the full text of the book for free:

• Chapter 1: Introduction
  • 1.1 What is in this book and what is not
  • 1.2 How is this book organized
  • 1.3 Prerequisites
  • 1.4 Acknowledgements
  • 1.5 Apologies
• Chapter 2: Vacuum tube basics
  • 2.1 Hydraulic valves as a metaphor
  • 2.2 Electronic vacuum tubes
• Chapter 3: Vacuum tubes as amplifiers
  • 3.1 Voltage and power amplifiers
  • 3.2 The loadline
  • 3.3 Operating point and bias
  • 3.4 Gain of the voltage amplifier
  • 3.5 Amplifier classes
  • 3.6 Biasing techniques
    • 3.6.1    Fixed bias
    • 3.6.2    Cathode bias or self-bias
    • 3.6.3    Gain of the voltage amplifier with self-bias
• Chapter 4: Integrated push-pull vacuum tube amplifier
  • 4.1 Output stage or power stage
    • 4.1.1 Single Ended configuration
    • 4.1.2 Impedance of an output transformer
    • 4.1.3 Reactive load and loadline computation
    • 4.1.4 Push-Pull configuration
    • 4.1.5 Push-pull advantages
    • 4.1.6 Push-pull loadline in class AB
  • 4.2 Phase splitter stage
  • 4.3 Input stage
  • 4.4 Global Negative Feedback
• Chapter 5: Power supply unit
  • 5.1 Power supply for the amplifier stages
  • 5.2 Power supply for the vacuum tube filaments
  • 5.3 Power supply for the fixed grid bias
• Chapter 6: Step by step design of a push-pull tube amplifier
  • 6.1 Design of the power stage
  • 6.2 Design of the input and phase splitter stage
  • 6.3 Global Negative Feedback
  • 6.4 Design of the amplifier power supply unit for the amplifier stages
  • 6.5 Design of the vacuum tube filament power supply
  • 6.6 Design of the fixed grid bias power supply

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Copyright © 2018 – Giuseppe Amato.
All material on this guide (pictures and text etc.) is covered by Copyright and all rights are reserved. No part of this guide may be reproduced without explicit permission of the author.