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Real McTube II photo
Build the "Real McTube II"
Overdrive/Distortion Tube "Stomp-box"

"The Real McTube" is a simple self-contained, one-tube circuit intended as an overdrive/distortion preamplifier. It makes use of the vacuum tube's relatively soft clipping characteristics to provide a fuzz-tone or overdrive sound with a warmer quality than afforded by most such solid-state devices. A dual triode is operated near the bottom of its characteristic curves to take advantage of the unique distortion of which such tubes are capable.

The project is intended for use with musical instruments, such as guitars and basses, to take advantage of the vacuum tube's distortion characteristics; as such it is not suitable for reproduction applications. If you're after high fidelity, consider my "quasi op-amp" preamp design instead.

The project is best assembled inside a closed case, stomp-box style, for ruggedness. However, there is no reason why you couldn't assemble it into other packages (even bread-board style). This is an ideal project if you have at least some electronics experience, but wish to break into the fascinating world of the thermionic vacuum tube.

of the "Real McTube" circuit
This project was originally published in Electronics Now, February 1999, based on a submission in 1997 of a circuit I put together in 1993. Since then, several individuals have made suggestions for expanding the text portion of the article, so here is an updated (Jan. 2001) version of this classic and useful design.

Back-issues of the Feb. 1999 issue of Electronics Now are still available from Gernsback, should you wish to look over the original design. Or click here to view the schematic for reference purposes.

Original Real McTube Article

The first page of the original "The Real McTube" article

  • High internal gain; Av = 2400 max. (over 65 dB)
  • 10:1 attenuator at output (-20 dB) 
  • 2-stage design 
  • Independent gain control at output of each stage 
  • Simple, low-cost power supply
    (using parts from two 12V "wall-warts") 
  • Very low B+ current demand (under 500 µA total) 
  • Low hum and noise
    (< 5mV. at max. gain; equivalent input < 2µV) 
  • Designed for 12AX7, but usable with any similar twin triodes 
  • Integrated bypass switch 
  • Readily customisable by changing component values to suit 

Copyright Notice:
All contents of this website, including all schematics, text, diagrams and photographs are Copyright ©1998, ©2001 by Fred Nachbaur, Dogstar Music. All rights reserved. This site may be freely linked, but none of the contents may be posted anywhere else without express permission of the copyright holder.

The information presented here may be used for personal, non-commercial use only. Any commercial applications of this design or any part thereof requires previous licensing arrangements with the author and copyright holder, Fred Nachbaur.

Article Index:

      1: Introduction

      2: Basic Tube Theory

      3: How It Works

      4: Building and Using "The Real McTube II"

      5: Parts List

      6: User Feedback

      7: About Tube Pin Numbering

Following is a listing of available resources for building the Real McTube II. Included are a printable schematic and this article in PDF format, as well as off-site resources based on the original 1993 design (published 1999).

new A new addition (Jan. 2003) is Francisco Peña's rework of the Real McTube design using a PC board, on his TonePad site. Pre-made boards may be available in the future, contact him for details.

Document: Filename:
Full Article (as per 1-5 above) mctube2.pdf rev. Sep 4 01
Schematic Diagram (7.5"x10") mctube2l.gif
Power Supply for 2-diode wallwarts (6"x3") mct2ps2l.gif
Original Real McTube, redrawn Euro-style AX-84 Project
Real McTube redesigned using PC board
(by Francisco Peña, used with permission)

You may contact me regarding this project at I'd be happy to hear from you, and any bug reports or suggestions for improvement are always welcome.

Goof at work
"Who's this goof?" ... um... that'd be me.
Around 1993, the year I developed "The Real McTube"

To find out what other kinds of trouble I get into, check out my sites listed below:

Free Music Downloads

Back to Tube Projects Main Page
My main Dogstar Music site
Fred's ZX81 retro computer page
My Theremin Exploits
Original music on
... and on Soundclick. Nice bio.
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