why a cathode resistor is needed in some cases and not in others. Or the audiophile who balks at the suggestion that maybe he should change not the brand, but the value of the coupling capacitor, if he wants to extend further the low frequency extension of his preamp. He replies that either the value is cast in titanium or that it would require a degree in physics to figure out a new value or that only the preamp designer could alter the value of that capacitor and only after paying large sums of money.
Why a Webzine?
   The original intent was to print a conventional magazine. We knew there was a need. The response to a query on our Tube CAD registration cards that a magazine devoted to tube circuit design found an overwhelmingly loud "YES". Still we knew difficulty and impracticality of starting yet another underground tube audio magazine.
    The web offers the publisher some great advantages over the traditional approach. World wide distribution. Free subscriptions. No paper (for those who must own a paper version, the size of the journal has been left small enough to be printed on to 8.5" by 11" three hole paper for compilation in a three ring binder). Live forums. No Post Office. Color. Motion. A hyperlink glossary.
    Schematics can now evolve, as the web allows for the easy display of animated GIF's, which display color and motion. Schematics can now show more than just part connections, they can reveal voltage potentials, current flow directions, and possibly, relative  impedances. 
    Math errors and typos will not live indefinitely on a paper page; once spotted, the web page can be corrected quickly. 
    We look forward to your letters, suggestions and contributions.  E-mail us:


Introduction to the
Tube CAD Journal

Welcome to Issue One
     The Tube CAD Journal is a monthly online magazine devoted to tube audio circuit design. Each month we will present some fresh looks at some old tube circuits and some altogether fresh tube circuits as well (yes, new tube circuits are possible). Circuits and more circuits. While we plan on covering complex tube circuits, like phono preamps or power amplifiers, our focus will be primarily on elemental circuits. Elemental circuits are the primary topologies, part configurations, arrangements that can stand on their own as recognizable functional circuits although they may be part of a larger circuit. A power amplifier circuit, such as the famous Williamson, comprises several sub-circuits: the Grounded Cathode amplifier, the Split-Load phase splitter, and the Differential amplifier, and finally, push-pull output stage. Just as we must understand how a resistor or a capacitor function in a simple circuit, we must understand the function and logic of these elemental circuits before we can understand more complex compound circuits.
       As these atomic circuits are like archetypal roles, mustached villain, white hatted hero, crusty, but actually soft-hearted boss, which can appear in many types of movies: western, mystery, sci-fi, each of these circuits finds application in infinite varied circuits: microphone preamps, SE amplifier, electronic crossovers, audio expanders and compressors, headphone amplifiers, and so on.... 

Moving On
    Armed with knowledge, the tube hobbyist can move beyond just being a mere part exchanger. Of course, part quality is of extreme importance to any quality audio design and part upgrading is an extremely cost effective way to upgrade a stereo system, but do not forget that the parts are only there because someone understood the structure and the logic of the circuit first. How sad and comical it is to see an audiophile, who equipped with a soldering iron and a platinum credit card, changes the resistor that feeds the LED on the front panel with a ten dollar bulk foil resistor in the hope of dramatically improving the sound of his system. Or the tube expert who can talk for hours on the superiority of one tube brand over another, but hasn't a clue

In This Issue

   1 Introduction to the Tube CAD Journal
2 Improving the Cascode's PSRR
4 Unbalanced to Balanced
6 Design Idea: Variable Feedback

     Glossary of Audio Terms   Copyright © 1999 GlassWare   All Rights Reserved