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Musical Instrument Tube Amp Building, Maintaining and Modifying FAQ

Much of this material applies to building or re-building hi-fi equipment, as well but it was originally intended for musical instrument crazies.

Authored, assembled and edited by R.G. Keen,
Most recent revision level is Version 2.10, 3/25/02

The first edition of this FAQ was first released in 1992.


Thanks to the contributors who helped and taught me:

Hundreds of folks who taught ME stuff when I didn't know a triode from a Tri-Axis; I can't remember all of your names, and it all comes out as general knowledge now, but I appreciate it. A few names in that category stand out:

And people who have contributed things that I have included as part of the actual text:

Special thanks to Nathan Stewart who did the bulk of the work converting the original version of this FAQ into HTML.

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  1. Basics of Tube Amps for First Timers
  2. Where can I learn about building tube amps?
  3. Where can I find parts to build/repair amplifiers?
  4. How can I modify my amp to be more powerful?
  5. How can I extend my tube life?
  6. How do I get...
  1. Where can I find plans for a Belchfire/Maximo/etc. speaker cabinet?
  2. Transformer questions:
    1. Do output transformers really sound different from one another? If so, why?
    2. Are the impedance tolerances the reason one OT may sound better than another?
    3. Are paper bobbins really better than plastic bobbins in output transformers? How about power transformers?
    4. Are differences in transformer sound in the pattern of the windings? Or something else?
    5. To copy a great sounding output transformer do you copy impedance or winding pattern?
    6. Is hand winding superior to machine winding for output transformers?
    7. What are "gaps" in output transformers, and why are they good?
    8. Can I use a push-pull OT in my single ended amp? How about if I re-stack it to have a gap?
    9. What is an "ultralinear" output transformer?
    10. Can I convert an amplifier with an ultralinear connected OT to normal use?
    11. Can I substitute two single ended transformers for a single plate-to-plate transformer?
    12. How do reverse biased diodes act as "transient spike preventers"?
    13. Can I use an ordinary pushpull output transformer as a single ended ultralinear output transformer?
    14. What does the "impedance" of my output transformer mean?
    15. Why do I have to match speakers to the output impedance of the amp?
    16. Will it hurt my amp/output transformer/tubes to use a mismatched speaker load?
    17. Can I use two single ended output transformers in a push-pull circuit and then parallel the outputs?
    18. What are the things about output transformer that cause the differences in tone?
    19. How can I tell if my output transformer is live or dead?
    20. Where can I get a good replacement output transformer?
    21. I want to make my own power and output transformers. How do I do this?/ Where can I find information about this?
    22. Should I replace my stock transformer with a new/old/vintage/purple one for better clean/grunge/grit/etc. sound?
    23. Are potted / impregnated transformers better? Is potting / impregnation necessary?

    Power Transformers

  3. What is the easiest way to get tube sound at a good price?
  4. How can I modify my tube amp to ... ? (also see recommended mods, below)
  1. When should I bias my amp and how do I do this?
  1. Amplifier Modifications
  1. Tube Characteristics and Substitutions
  2. Maintenance Issues
  1. Appendix A. Tube Stuff Suppliers
  2. Appendix B. Tube Makers Producing Today (Eric Barbour news posting)

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Basics of Tube Amps for First Timers