Electronic Design

Bob's Mailbox

Hi Bob: I have been a reader of your application notes and articles for years and have always enjoyed your writing. Lately, your articles (for example, on the K2-W) have reminded me of two Monty Python actors reminiscing about the past: "You lived in a cardboard box? We dreamed of a cardboard box.

We slept on gravel in the middle of the road and had to move every time a car came along...." The biggest difference is the subject. Now it is more like:

  1. You had a 300-baud modem with acoustic coupling? We dreamed of a 300-baud modem. All we had was a battery and two wires and we had to tap out ASCII code.
  2. You had a battery and two wires? We dreamed of having a battery. We had to whistle into the handset and listen to the return tones to write our computer programs.
  3. You had a phone you could whistle into? We dreamed of a phone. All we had was....

(Check. We dreamed of vacuum tubes. We only had relays and had to file their contacts every night. /rap) You get the idea. I enjoy these "electronics war stories." I am guilty of doing that kind of thing myself. Ever tried to convince your student that 8-in. floppy drives existed? Keep up the great articles.

Lawrence King (via e-mail)
Pease: I know a friend who has a hard-drive disk that's 42 in. across. Thanks for the comments.

Dear Bob: Your column on the Philbrick K2-W (Electronic Design, Feb. 3, p. 22) brought back memories of experimenting with ±300-V dc op amps. As a recent graduate, I was part of a team at Melpar Inc. that was developing an analog formant vocoder well populated with K2-Ws (three tabletop racks). I was also responsible for designing the vocal pitch-measuring circuit. I had a breadboard circuit (yes, on a length of 1- by 12-in. plank) spread out on the bench, fed by a microphone. My Glorious Leader was looking over my shoulder and decided to reverse the phase of a coupling transformer (with the circuit powered up). The ambient noise in the room gave him a small shock, resulting in an "ouch," followed rapidly by "OUCH," and "OUCH!!!" as he became part of an unstable feedback loop.

Ralph Gaze (via e-mail)
Pease: Uh, yeah, a K2-W is NOT guaranteed to NOT swing more than ±99 V!! And, there are circuits where the amplitude could grow gradually! YIPES! Thanks for the story.

Dear Bob : I was wondering if you know where I can find an I versus E curve for Copper-Oxide rectifiers. I don't think that this type was listed in your Troubleshooting Analog Circuits appendix E chart. Any ideas?

Dale Roche (via e-mail)
Pease: Hello, Dale, I don't think I have ever seen that curve! But I'll ask around. Nope, ain't found one yet.

Hello Bob: I am searching for some beam power tubes and thought I would give you a try. I am specifically looking for a 6417 and/or 7551. Both are nine-pin types typically found in mobile VHF power-amp applications in the 1960s and early 70s. Have you any collecting dust in the junk box? (No. /rap).

Dennis Monticelli (via e-mail)
Pease: I tried www.dogpile.com and shortly found www.thetubecenter.com/tubelist11.html. It has 6417s at about $6 and 7551s at $9. I just searched for "6417 tube." I quit at this one Web site that had both. Have fun looking further. Dogpile often beats Google. Also, www.hamtubes.com/tubes/list5.htm also seems to have both types for the same price.

Hi Bob: In the preface to Morse and Feschbach's Methods of Theoretical Physics, thanks are given to, among many others, Robert and Jane Pease. Were you a really advanced child prodigy, or are these relatives?

Steve Heider (via e-mail)
Pease: No, that was not me, nor is it anybody I know. There are LOTS of Peases around.

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