[Amps] Decline of homebrewing?

[Steve London]

Excellent advice, Jim.

I was nearly killed at age 15. Thank goodness the mic cord/HV ground 
return broke when I jerked backwards. The muscle contraction kept me 
from letting go of the D-104. I still get knots in my stomach when I 
think about this incident.

73,
Steve, N2IC

On 01/06/2017 09:07 PM, Jim Garland wrote:

>
> I don't want to be argumentative, but I think the above perspective is
> dangerously misguided. I've been homebrewing ham equipment since I was
> twelve, starting with a Heathkit AT-1. At age thirteen, a ham buddy and
> I were playing "Hot Potato," by tossing a charged ten microfarad 1000V
> oil capacitor back and forth. He caught it wrong and the shock knocked
> him to the ground and sent him running crying to his mom. Stupid. At
> sixteen, I built a homebrew amp running four 6AG7s, stealing the HV by
> running a piece of hookup wire clipped to the plate cap of the 6146s of
> my AM rig, across the desktop, to the amp. Also stupid. At seventeen, as
> a senior in high school, I unscrewed the coax connector to my pair of
> 813s, not realizing that the coax braid was the ground return to the
> 2000V power supply. I was thrown across the room and dislocated my
> shoulder when I crashed into the wall.Stupid, maybe. Ignorant, very.
>
> Fast forward six decades, and I'm still homebrewing. My most recent
> project (a duo-band 80m/160m amp running three GU74Bs), took three years
> to design, build, and debug. The design and circuitry is my own, and the
> enclosure, metalwork, printed circuit boards, etc., are homemade. The
> transformers were custom made, and with a few exceptions all the parts
> were new and unused. I've not added up the cost, but I probably spent
> $3000 on it, spread over three years. It's probably the best thing I've
> ever built. I mention this, not to show off, but to make the case that
> I've paid my dues by spending most of life reading and studying and
> experimenting and building electronics. A year or so ago, I wrote an
> article for QST/QEX (one of many over the years) on one of my HV power
> supplies. In it, I summarized my personal safety rules which have
> probably saved my life several times. Here they are. Please note,
> especially, number two in the list:
>
> 1. Don’t let your reach exceed your grasp. This is not a project for
> beginners. You should not attempt to build [a high power amplifier]
> unless you’re a seasoned builder who has experience with high voltage
> circuitry.
>
> 2. Young amateurs should not attempt this project. Working with high
> voltages requires the maturity and patience that come with age and
> experience.
>
> 3. Never work around high voltage when you are tired, stressed, or in a
> hurry.
>
> 4. Never work around high voltage after drinking alcohol. Even one beer
> or glass of wine can impair your judgment and make you careless.
>
> 5. Before working on a high voltage power supply, always follow these
> three steps: /Unplug/ (the AC power cord), /discharge/ (the filter
> capacitors) and /verify/ (that the output voltage is truly zero).
> Time-honored practice is to use a “chicken stick” (a wooden dowel or PVC
> tube, with one end attached to a grounded wire) to make sure filter
> capacitors are completely discharged.
>
> 6. When working on a high voltage power supply, remember that a
> dangerous time is after the power supply has just been turned off, but
> before the filter capacitors have fully discharged. A 50 µF capacitor
> charged to 4000 V holds a potentially deadly 400 Joules of energy. Even
> with bleeder resistors, it can take a minute or more to discharge fully.
>
> 7. When removing a recently discharged filter capacitor from a power
> supply, tie the two terminals together with wire. Large high voltage
> capacitors can self-charge to dangerous levels if the terminals are left
> floating.
>
> 8. Don’t stake your life on the expectation that bleeder resistors,
> fuses, circuit breakers, relays, and switches are always going to do
> their job. Even though modern components are very reliable, it is safe
> practice always to assume the worst.
>
> 9. Don’t build this power supply if you don’t understand how the circuit
> works. High power amplifiers and power supplies are not “plug-and-play”
> projects with step-by-step instructions. Builders must be knowledgeable
> enough to improvise, make component substitutions, and implement design
> changes.
>
> 10. With high voltage projects, it doesn’t pay to be “penny wise and
> pound foolish.”Use high quality components throughout and save your
> forty-year-old junk box parts for projects where safety and reliability
> are not paramount requirements.
>
>
> So I don't know about the rest of you, but this is what I've learned
> from the School of Hard Knocks.
> 73,
> Jim W8ZR
>
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