#### Book Description

This book is a step-by-step tutorial for simulating vacuum tube guitar amplifiers using LTspice, a free SPICE-based electronic circuit simulator for Windows and macOS. The book walks you through the basics of developing a schematic, setting up a simulation, integrating vacuum tube models, and interpreting the results. From there it gradually ramps up to advanced topics, like verifying the sonic performance of a guitar amplifier as a complete system, analyzing the dynamics of overdrive, and writing new SPICE models for triodes and power tubes. With this book, you will learn how to

- analyze tone-shaping circuits,
- simulate real-world components,
- evaluate the performance of a tone stack,
- compute a power supply's DC output voltage under load,
- determine the effects of negative feedback for single-ended and push-pull power amps,
- measure the dynamics of harmonic distortion in preamps and power amps, and
- analyze transient behavior when stages are overdriven.

#### Author

Richard Kuehnel is a member of the Circuits and Systems Society of the Institute of Electrical and Electronic Engineers.

#### Introduction

##### Warning: High Voltage!...1

##### Computer Simulation of Guitar Amplifier Circuits...1

##### SPICE Models for Vacuum Tubes...3

##### LTspice: Windows versus macOS...6

##### Acknowledgements...7

#### Chapter 1: An LTspice Tutorial

##### Analyzing Tone-Shaping Circuits...8

##### Simulating a Real-World Capacitor...16

##### Simulating a Real-World Resistor...20

##### Creating a SPICE Model for a New Component...24

##### Analyzing a Tone Stack...33

##### Determining a Tone Stack's Input Impedance...37

##### Computing the Effective Grid-Stopper Resistance...39

##### Computing a Power Supply's DC Voltage Under Load...42

#### Chapter 2: Creating a Triode Small-Signal AC Model

##### A Triode Model from Discreet Components...50

##### Converting a Triode Model into an LTspice Component...54

##### Measuring Frequency Response for a Preamp Stage...56

##### Measuring Signal Levels in dBV...61

#### Chapter 3: Power Amp AC Modeling

##### Single-Ended with Negative Feedback...65

##### Push-Pull with Negative Feedback...68

#### Chapter 4: Audio Analysis of a Guitar Amp as a Complete System

##### System Design...72

##### Translating the Schematic into an Audio Model...74

##### Input Jack to Speaker Jack Response...83

#### Chapter 5: Using Downloaded Large-Signal Tube Models

##### Classic Tube Models Based on Space Current...86

##### Tweaking the Space Current Model...87

##### Koren Triode Model...87

##### Koren Tetrode and Pentode Model...92

##### Automated Parameter Extraction Using ExtractModel...95

##### Derk and DerkE Pentode and Beam Power Tetrode Models...95

#### Chapter 6: Create Your Own Large-Signal 12AX7 Model

##### Modeling a Specific Circuit for Greater Accuracy...100

##### Using a Behavioral Current Source...102

##### A Space Current Model with a Variable Exponent...104

##### Modeling Plate Current Nonlinear Behavior...114

##### An Improved 12AX7 Grid Current Model...123

##### Finalizing the Model...133

##### Simulating the Effects of Grid Current...134

##### Measuring the Dynamics of Harmonic Distortion...135

#### Chapter 7: Create Your Own Large-Signal 6L6 Model

##### Modeling a Specific Circuit for Greater Accuracy...146

##### The Plate Current Model...147

##### Step 1: a Fixed Screen and Grid Voltage Model...149

##### Step 2: a Fixed Screen Voltage Model...153

##### Step 3: a Generalized Model...161

##### The Screen Current Model...168

##### Step 1: a Fixed Screen and Grid Voltage Model...168

##### Step 2: a Fixed Screen Voltage Model...172

##### Step 3: a Generalized Model...177

##### Operating Point Simulation...183

##### Transient Simulation...186

##### Measuring the Dynamics of Harmonic Distortion...187

##### Analyzing Transient Behaviour During Overdrive...191

#### Some Final Words on Guitar Amplifier Simulation

#### Index