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.TITLE: Design and Construction of Tube Guitar Amplifiers
AUTHOR: Robert Megantz
..DATE: 2009
.PAGES: 162
...PUB: TacTec, San Jose, CA, USA.
..ISBN: 978-0-615-29180-2
.PRICE: $29.95 + $3.25 s/h
Mr. Megantz has written a very well done "...technical book for non-technical readers." In four chapters, he provides simplified, easy to read and understand descriptions and examples using only simple algebra (no calculus, yeah!), with numerous "...how it works..." examples drawn from Fender Deluxe, Champ; Ampeg GU-12; and Magnatone M7 amplifiers.
Chapter 1 provides the obligatory "Introduction 101" information needed to understand the basics of electronics. His simplification of capacitor and inductor oppostion to current flow as "...impedance (Z) with a phase shift..." is both noval and technically correct. The immediate introduction and use of Decibels to explain "gain/loss" consistently thoughout the book as well as the inclusion of the seldom taught, but immensely practical and useful "Rule of 10" concept are applauded. The three vacuum tube constants are presented and explained but only plate resistance (rp) is actually used further in the book. Yes, it can be that simple!
Chapter 2 starts with the triode circuit, then adds volume and tone circuits using worked examples. In the "Output Stage Driver" section, the cathode follower is introduced and explained as introduction to phase splitter circuits: the simple, one-tube Concertina/Split-Load which has no gain, and the two-tube long-tail or Schmitt differential circuit which does provide gain. Even the frequency selective negative feed back aspects of the Fender "Presence" control is explained. Simple single-ended and push-pull circuits are presented and explained, although little is mentioned about Class-A versus Class-AB1 operations, only their fundamental differences. Also included is a simple worked example of negative feedback applied from output back to the phase invertor input (Fender Deluxe Amp)...so, now you know what the 820 and 47 ohm resistors actually do!
Chapter 3 illustrates how and why effects are implemented. A brief introduction to types and sources of "Distortion" is provided but does not describe how it is actually calculated (maybe next edition?). The section on "Overdrive" unfortunately has a printing error, the top portion of Figure 3.6 'Preamplifieir with Overdrive" is not printed. The Fender two-tube and Ampeg one-tube reverberation circuits are compared and contrasted. Effects Loop input and output circuits are described using example circuits, but are not designed (next edition?)
Chapter 4 tells you how to "put it all together"...literally. Physical electronic components and hardware are illustrated and described. The only complaints I found here were: (a) there was no information provided on how to determine the correct choke "size" to use, only the statement "...for most power supply applications, inductance should be between 4 and 10 Henries." and (b) no mention of precautions for using "make-before-break" versus "break-before-make" switches. The "Initial Power-up" section contains a very good, step-by-step explanation of what needs to be done and why.
Appendix A lists two electronic component suppliers and six specialized components sources for tube amplifiers.
Appendix B provides brief summary tube data on common preamp, power and rectifier tubes:
12A_7 tubes (12AX7A/12AU7/12AT7...)
6BQ5/EL84
6V6GTA/6AQ5A
6L6GC/7027A/5881/KT66 (what about the 7581A?)
6CA7/EL34/KT77
6550/KT88
5Y3GT
5AR4/GZ34 (60 µfd capacitor limit isn't shown)
SUMMARY -- 3.7 out of 5 stars. I liked it for its simple, thorough, treatment throughout. Yes, I'd recommend it to both the "newbie" as well as the "curiously experienced" reader. It's easy to read and understand and not very math intensive.