Electronic Design

Bob's Mailbox

I recently picked up a Tektronix 284 Pulse Generator from eBay. The 284 is used for scope calibration/performance evaluation. A few weeks later I got the manual for the same product—from eBay, of course. The manual was dated 1986, but the first printing was 1967! In 1967, I started my first engineering job right out of college.

Anyway, I was fascinated with less than 70-ps pulse-rise-time circuitry that incorporates a tunnel diode. So, I thought it would be fun to build a tunnel-diode pulser for my own amusement. Tektronix doesn't supply the TEK 284 tunnel diode. I then asked the original maker of the TEK tunnel diode, Germanium Power Devices Corp., for pricing and availability. They want a mere $250.00 each (Qty. 1-99) for the SMTD892 tunnel-diode device, and a three-week lead time.

Yeah, I'll take a hundred. <LOL> I'm sure there are more tunnel diodes sitting in garages than there are on the shelves of distributors. It's disappointing when you can't get your hands on some of the old discrete parts to play with—takes some of the fun out of engineering <IMO>.

I'm waiting for a reply to an e-mail sent to American Microsemiconductor, inquiring about their tunnel diodes. I asked for ten diodes each of three types, so those guys must be really excited about that order of perhaps $7,500 worth of parts. I made my request before I discovered that a $250.00 diode really existed on this planet.

I design analog circuits, often with discrete components, and often purchasing components from obsolete semiconductor parts houses! Try to purchase a 2N2222A from Newark— the part is now obsolete! I suppose I'll be retired within the next 20 years (I'll be 75 by then), so hopefully the completely depleted stock of all discrete semiconductor components won't have much of a personal impact on me. <grin> But it will eventually be very difficult, sometime in the future, to build some of those specialized circuits that an off-the-shelf IC can't provide.

Oh well, the above represents all of my gripes for this week. Next week I've got a smog check on an Audi. <groan>
BILL RUSSELL, Sr. Electronics Engineer
Digital Instruments Inc.
Santa Barbara, Calif.
via e-mail

You can buy a "PN2222" or similar, in plastic, which is more reliable than most of the MIL-2N2222s that were ever built, unless you flog them above 100°C of junction temperature. Hey, nobody is BUYING real 2N2222s. I bet you can buy JAN ones for $20, but even my rich Uncle Sam isn't buying. Nobody is buying tunnel diodes either. If you just want to see subnanosecond rise times, then setup a couple of "PN918s" or similar as an emitter-coupled multivibrator. That will get WAY below 1/4 ns.—RAP

Hello Mr. Pease:
I enjoy your column in Electronic Design, and always read it first when my copy arrives. I'm sending to you by regular mail a copy of an article entitled "Sound Man," from the March 26 issue of the Boston Globe Magazine. Its subject is Vladimir Shushurin and the very high quality, very expensive ($16k to $30k) stereo amplifiers he hand makes.

He contends that the conventional total-harmonic-distortion values advertised for commercial amplifiers don't translate to good sound. His philosophy is described in the article, and I would like your thoughts on whether most listeners could notice much difference between his and typical stereo components that most of us buy. (My guess is that MOST of us probably cannot. More on this later. But if someone wants to, fine, let him pay. /RAP) Congratulations on writing such interesting and readable columns on a variety of topics!
KEN MORMAN, Quality Engineer
FLIR Systems
via e-mail

Hi, Ken. I'm sure he is, in many cases, right. However, if he says there are NO GOOD SOLID-STATE amplifiers that sound good, hey, I'd like to challenge him to a really blind test! Especially compared to a good amplifier costing 1/5 to 1/10 to even 1/20 of what his cost.—RAP

Hello Bob:
All of your arguments on "over unity" etc. also were applied to the Curies' in their day. They were actually accused of trying to build a perpetual-motion machine. (I didn't know that, but I'm not surprised. /RAP)

I use my spare time to explore the impossible (low temperature/energy nuclear reactions). I'm not entirely sure these reactions are nuclear, but for now nothing else explains them. Ten years ago this was thought impossible, but not anymore. (MOST people still think they are impossible, but I don't. Yet on the other hand, I do not foresee that it will be EASY! Do you think you can get the tritium to make a lot of power output? /RAP) Don't throw the baby out with the bath water. We have not yet discovered all things in this universe.
via e-mail

Agreed! Give it a good try, Bruce! Best wishes.—RAP

All for now. / Comments invited!
RAP / Robert A. Pease / Engineer
[email protected]–or:

Mail Stop D2597A
National Semiconductor
P.O. Box 58090
Santa Clara, CA 95052-8090

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