This interesting discussion about homebrewing techniques and safety
brings to mind an experience I had a few years ago with my StationPro
station controller. I designed the StationPro for myself, but it seemed
to be a useful enough station accessory to warrant writing up the design
in QST. After publication, I had a couple of offers to manufacture wired
and tested versions, but ended up only making bare PCBs and enclosures
available, primarily to encourage homebrew activity. (I've done this
with other projects over the years.) The StationPro is a lengthy
project, requiring nearly twenty hours of assembly time after the parts
are collected. It's also not cheap, about $600, so it's a big investment
in both money and time for most builders. That said, the assembly is not
complex. Putting together the kit consists of following illustrated,
step-by-step instructions. The builder stuffs five printed circuit
boards (with a photo of each component), mounts them in two prepunched
and silkscreened enclosures, and plugs them together with ribbon cables.
Easy peasy, right?
As it turns out, no. What I didn't realize was how basic techniques that
I took for granted were new and unfamiliar to many of my builders
(roughly 350, to date). Simple stuff, that I'd never thought about: How
tight should the mounting studs be on a DB25 connector? What's the
difference between a machine screw and a self-tapping screw? Which way
do you hold the resistor to read the color code? And no, it's not okay
to use a 100W soldering gun on a 25 pin IC.
What really surprised me, though, was how things that seemed to be
common sense to me, were things that some of my builders (not all,
fortunately!) had never thought about: gathering the correct tools
together before starting work; having a clean, uncluttered workspace,
using a bright light to illuminate the work, keeping the cat in the
other room, turning off the TV, being systematic and careful and
checking your work.
Here's an example. Part of the StationPro assembly requires running
short wires from two microphone connectors to carefully labeled solder
pads on a PCB. What could be easier? Well, this part of the assembly
turned out to be an exercise in frustration for several builders, to the
point where I finally wrote up a little article for them, "W8ZR's Tips
for Wiring Circuit Board Jumpers." You can read it here:
http://w8zr.net/stationpro/images/download%20files/Tips%20for%20Wiring%20Circuit%20Board%20Jumpers.pdf
My point is that one shouldn't take for granted, as I did, the
importance of experience and practice in developing homebrewing skills,
even for very simple projects. And just as important as skills is
judgement and maturity. If you're going to be good at almost any craft,
you can't be impulsive, or overconfident, or unaware of your
surroundings, or easily distracted, or in a hurry, or unwilling to
accept advice. And that's why I worry about teenagers undertaking
projects involving lethal voltages. I'm sympathetic to the idea that one
can be overprotective with young people, and that they'll never learn to
be self-reliant if they're forever coddled and shielded from risk. And I
agree that the pendulum may have swung too far in that direction in
modern society. But I also believe that one has to crawl before one can
walk. Ideally, one's parents or an elmer (or staff sergeant!) should
provide guidance to beginners, but unfortunately that isn't always
possible. It wasn't possible for me, and from some of the stories I've
been reading about the past couple days, I'm not alone. Sorry, but I
strongly believe hams should start with simple projects to acquire first
the skills and wisdom required to build a high power RF amplifier. The
stakes are too high to just plunge ahead and hope for the best.
73,
Jim W8ZR
On 1/7/2017 9:14 AM, Ward Silver wrote:
> Excellent advice, Jim.
Hear, hear!
And another good piece of advice is to make sure you have an ac safety
ground connection on every metal enclosure. With 12 Vdc being the
normal power supply voltage these days, we can get away with practices
that would really be hazardous for tube-based gear.
> A 50 uF capacitor charged to 4000 V holds a potentially deadly 400
Joules of energy
In the defibrillator business of a few years ago, this was known as
the "rescue shock" of last resort. This amount of energy can lift a
200-pound person 1.5 feet. When leveraged by muscle-and-bone, much
damage can be done.
73, Ward N0AX
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