>
>> A good friend and famous multi-multi contest station owner, Phil
>> Ashcraft, was killed while adjusting the tuned input on his 4X1 amp.
>> All HV is lethal, but when you get past 5kv, one little mistake will
>> probably be your last. The HV contacted his watch band, and "welded"
>> his arm to the B+.
>>
>> Things that would never break down at 4kv such a components,
>> insulation, and even arcs in open air are not unusual. Take all the
>> precautions you can, especially when the covers are off. Amp builders
>> are a dying breed...lets hope we will all go SK by natural causes.
>
>
>I was almost killed by using the resonant choke circuit in Bill Orr's
>handbook.
>
>I used the formula he suggested and build a resonant choke filter,
>not knowing you really must have resonance above the ripple
>frequency.
>
>The supply was a small 5kva pole pig with a bridge, driving a choke
>input filter..for a pair of 3-400's. I used big oil filled caps that had
>very high voltage ratings, they were from the utility company.
>
>When I powered the thing up, the 3-400Z's would arc from their
>anodes to the grid support. When I disconnected the anodes of the
>tubes, the blocking capacitor exploded on power up. When I
>disconnected it, the bypass capacitor exploded.
>
>I placed a 5kV meter IN the ps cabinet, and attached it through a
>HV insulated test lead (40kv rated) to the HV supply positive rail.
>
>I stood back (on a rubber HV blanket), kept one hand behind me,
>and flipped a panel mounted toggle switch on. There was a flash
>and the HV lead blew in two. It snaked OUT of the cabinet and
>landed on my wrist (about two feet from the leads original position)
>on the hand that was holding the grounded toggle switch. The only
>thing that shut it off was the main fuses eventually opened.
>
>It burned a charred half-dollar sized hole in my wrist, and caused
>second degree burns up to my elbow. I still have the imprint of the
>toggle switch between my thumb and index finger!
>
>So what crossed my mind? I thought "Shit, how long will my brain
>work now that my heart is stopped?" So I watched the clock on the
>wall. When I saw the second hand make two complete sweeps
>around the dial, I thought "darned, it didn't kill me".
>
>If I was not working on a rubber HV mat, and did not have the habit
>of working with one hand...I'd have been toast.
>
>BTW I wrote Bill Orr a nice letter about this, and suggested he
>might warn people about it in the area where his handbook
>suggests using resonant filters. I have no idea if he ever changed
>his book.
My guess is that he did not correct his book. Orr was somewhat less
than eager to admit to mistakes.
cheers, Tom
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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