[Amps] Decline of homebrewing?
Roger (K8RI)
k8ri at rogerhalstead.com
Tue Jan 10 18:56:06 EST 2017
As for a 2 man rule, they didn't practice that even in the shop when
working with multi ton power transformers inside their cages.
Every one should have the experience of being about 3 or 4 feet from a
50,000 Joule Varistor when it is vaporized leaving the #8 leads pointing
straight out. We (those who worked on live power packs) made it a
practice to never get in front of those varistors and to never look at
one. Their departure was accompanied by a brilliant/blindly bright flash
and it was LOUD! BTW those transformers were about 5' X 5' and heavy
enough we had to put 3 or 4 men on the back end of the standard fork
lift to keep the back wheels on the pavement. Otherwise the forks never
lifted the transformer.
I can think of many times I was "nearly" killed, but none have to do
with HV...well maybe one, but I don't think of 500 VDC as high voltage
after working with 200KW, and more RF generators. The Hallicrafters PS
for the series of rigs, HT44, SR150, SR160 and maybe more, had two jacks
on the chassis for measuring plate current. I was actually up on the
equipment bench where the station was set up. This home brew table was
the standard height above the basement floor, or a few inches shy of 3 feet.
I had the probes from a DVM stuck into those jacks on the PS. I had to
reach over to move the DVM. This DVM had a painted steel case and bare
metal handle. Unbeknownst to me, my fingers had slipped down and were
touching the probe tips. IIRC those jacks were on the ends of a 10 ohm
resistor "in the HV line". So I had just shorted the 500 plus VDC to
ground through me. No, it didn't throw me. There is a big difference
between grabbing hold of something and touching it. "Both" cause
violent muscle contraction, but the results are quite different. That
sucker had me! In one arm and out the other with my heart in the middle.
I was aware of the pain and then I was laying on my back on the concrete
floor, gasping for breath.
I had apparently curled up, gone unconscious, and rolled forward off the
bench, (breaking the connection). I had landed on the floor, right in
front of the bench.
At any rate, I was back among the living, although gasping for breath
and sweating like crazy. I had cheated death once more.
73, Roger (K8RI)
On 1/8/2017 9:57 AM, Charles Farr wrote:
> Doesn't anybody remember the "2 man rule"? I have individuals that
> belong to my lodge that work alone, even though I constantly remind
> them to get someone to be with them. Another valuable lesson from the
> military experience.
>
> Chuck, W6AJW
>
>
> On 01/07/2017 10:13 PM, Jim Thomson wrote:
>> Date: Sat, 07 Jan 2017 21:30:23 +0000
>> From: Manfred Mornhinweg <manfred at ludens.cl>
>> To: amps at contesting.com
>> Subject: Re: [Amps] Decline of homebrewing?
>> Steve, and all,
>>
>>> I was nearly killed at age 15.
>> ## heres my sob story. I was building a heath GR-64 SW rx between
>> xmas + new year 1969. Age 14
>> My mum was cooking dinner, and I was in the den, just off of the
>> kitchen. I had just finished building the
>> kit after several days..and a had 3-4 components left over. Thought
>> to myself that heath was not too smart to
>> be supplying parts that were not required. Of course, when plugged
>> in and turned on.... it was dead silent.
>> I take off the lid, and flip it upside down.... and this is a tube
>> RX. I start probing around...with my fingers....with zero test gear,
>> then got zapped with 300 vdc off one of the filter caps..it was
>> unplugged too. Let out a scream, and went flying across the room.
>> Mother
>> freaked out, and figures Im in way over my head, and has a fit.
>> Being from the UK, she thinks nobody should touch anything unless
>> they have 1st completed the 7 year apprenticeship in the appropriate
>> field. My older sisters boyfriend at the time was a physics
>> lab instructor at the local university, and had a lot of experience
>> with HB electronics..and also fixing every heath / dynaco / knight
>> kit in town.
>> He fixes it in a few hrs, and all is well. 3-4 components were
>> indeed required.
>>
>> ## fast forward to 1974. Bought a used HB 2 x 813 amp..with
>> NO B+ voltage meter. Great fun driving it with 200 w po from my
>> used
>> drake TR-3 xcvr. 1100 w out. Nobody even knew what IMD was back
>> then, and could care less. I short out the filter choke on the
>> fully exposed
>> B+ supply, for even more B+.
>>
>> ## wanting more power, around 1976, I buy a used HB single
>> 3-400Z rf deck, no cabinet, no B+ meter, and no B+ supply. I build
>> a hb 5 kv no load B+
>> supply, and also cabinets for both the B+ supply + the RF deck.
>> Filter caps were a mess of series and parallel 2-4-6 uf oil
>> caps....and no bleeder. Drove the
>> 3-400 Z with the TR-3. No tuned input on the rf deck. 1700 w out of
>> a single 3-400Z. Tube ran bright orange to sorta yellowish.
>> Was working out of town those days, a week at a time. B+ supply
>> had been OFF from sunday eve to the following friday night. 4 inch
>> diam muffin was sorta loose,
>> so tightened it with an xcelite nut driver. Tube was in the way,
>> so tried to work around it. Tried tightening the top pair of corner
>> screws, and shaft of nutdriver
>> was touching the glass. Shoulda yanked the tube but was in a
>> rush, contest on that weekend. To get the driver to fit, I slide my
>> fingers down onto the steel nutdriver shaft,
>> and try to get the nuts tightened. Wearing a T shirt with bare
>> arms exposed. Nut driver shaft touches the plate cap of the
>> 3-400Z..and also had both forearms resting on the
>> aluminum box. Top lid was removed. I get thrown 7 feet across
>> the room, and wake up 5 mins later..dripping in sweat.
>>
>> ## lesson learned was oil caps will stay charged for at least 5
>> days..... esp when stupid enough to not include a bleeder.
>> After that it was B+ meters wired in both the RF decks and also the
>> external B+ supplies. Bleeders used, and ditto with shorting sticks
>> etc.
>>
>> ## Got zapped a few times while working at the telco....and each
>> time was up 7-10 feet off the ground on a rolling ladder. AC is bad
>> news.
>> B+ will throw you across a room..and both will easily kill you.
>> Had a buss bar explode in my face while trying to pry a stuck fuse
>> out. Blew
>> a hole in the square shaft of the large screwdriver I was using at
>> the time. I almost had it out when the shaft touched the partially
>> recessed mounting screw
>> for the insulator block assy..in the rack. I had shorted the input
>> buss side of the bank of fuses. Now you know why there is at least
>> one guy in every
>> telco office nicknamed ..... sparky.
>>
>> Jim VE7RF
>>
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