In my last column, I promised to tell you how we fixed the "selective-fit" problem with the K2-XA op amp.* Let's take care of that before we get to this month's letters. The "final solution" for the K2-XA was to add a transistor to the circuit (see the figure). This allowed the circuit to hold the pentode's cathode at 120 V.
With a total 420-V supply, the 6BR8A's plate could easily swing 240 V p-p, and the problem of swing and "selective fit" went away. Admittedly, the test tech had to select and install a selected resistor in the positive feedback loop. This resistor did correlate approximately with the beta of the npn. That npn was an SM1009 or SM1011, a fairly high-voltage npn silicon Mesa that we bought from TI. After that, we never had any problem with "selective fit." But we sure did all learn a tough lesson about "selective fit." Sometimes "selective fit" does get some good things. Other times, it leads to trouble!! /rap
Dear Bob: Greetings from Idaho! My uncle and I read your article, "What's All This Clinometer Stuff, Anyhow?" (Aug. 9, p. 20) with interest and amusement. As you're a highly acclaimed electronics design engineer, we think that you could have used a strain gauge, a hot-wire anemometer, and a microcontroller for this project. (Yeah, but I certainly would not use such a scheme without good battery life! As I mentioned, I needed to keep the whole thing down at 1 ounce. Including batteries. /rap)
Or, may we suggest the Lev-O-Gage clinometer, available for $12.99 from West Marine (www.westmarine.com)? To quote my sailor uncle, "Your roads are probably smoother than a rough sea."
Kris Willoughby (via e-mail)
Pease: Some of our roads were smoother. But, some of our roads were staircases. Is that rough enough for you? Obviously, no clinometer is going to make sense of that!
Dear Bob: I'm glad to see you helping to tell the world that PowerPoint is a prolific source of artificial stupidity (March 29, p. 18). Here is how I sum up the PowerPoint mindset... Original text:
Roses are red, violets are blue, Sugar is sweet, and so are you.
After running through the PowerPoint mind:
Seriously, have you noticed that weak PowerPoint presentations lack verbs? They're just lists of things to talk about; they don't actually do the talking! (But people who use PowerPoint have been told not to put too many words on one foil. So they leave out "unnecessary words" and only put in the key words. You gotta admit, if you put up the whole poem, and people can just read it, it takes away all the suspense! People do altogether too much reading of their own foils!! I minimize that, usually. /rap) And the fancier the background picture, the emptier the content!
Michael Covington (via e-mail)
Pease: That's just my point! All the effort went into making a pretty view, and no thought went into the contents. Usually.
Electronic Design has put up about 125 of my most recent columns and about 85 recent Mailboxes. Go to www.national.com/rap and click on ED columns to get to www.elecdesign.com/Departments/DepartmentID/6/6.html. The index works pretty well and is chronological. There's a lot of good columns in there—even old ones that were not in there a few years ago. /rap
Comments invited! [email protected] —or:
Mail Stop D2597A, National Semiconductor
P.O. Box 58090, Santa Clara, CA 95052-8090