Some how this ended up in my "Drafts" folder after I started it early
today and I just got back to it so I'll address a couple other posts.
TexasRF@aol.com wrote:
> But, but, but, In a design with a grounded screen, there will be
> screen current showing due to the dc current generated from plate
> voltage flowing through the water to ground.
True, but just sticking in probes is only going to give a relative reading.
>
> With say, 3kvdc, and 50,000 ohms, the current would be 60mA. So, it
> seems a resistivity of 5 Megohms or more might be desirable.
>
Also the path of the water flow through non conductive hoses (we coiled
ours) only has to be a few inches to put that resistance into the
multimegaohm range. So even with 50K resistivity (It's usually higher) a
10 inch hose with an internal cross section of 1 CM would represent 500K
plus. A 1/4 inch tube (OD) would have a much smaller cross section and
thus a still higher resistance. Given the benefit of the doubt a 1/4"
tube with a 3/16" ID (it's more like 1/8") would have an area of about
0.1 sq inch, so the resistance would get quite high.
As to DI Vs Distilled, I don't know why the company went that way. I've
always used distilled. However the drains they used were open to give a
visual that all pipes/tubes had water. This meant the water which was
usually quite warm had a considerable evaporation rate and I think we
added about 50 to 100 gallons per week. That meant the DI became *very*
aggressive. It was not uncommon when working on one of the generators
to have a brass 1/2" or 3/4" hose barb crumble in your hands. As long as
nothing disturbed them they'd last a long time, but even with regular PM
we'd occasionally have one let go spraying water all over inside the
generator. Depending on the generator that might or might be
expensive, but if it failed while running, the lost product was
certainly expensive, particularly back in those days. I've mentioned it
before, but a half inch diameter slice of Intrinsically pure single
crystal silicon sold for about $160 a gram. Now they grow poly crystal
that is more pure right out of the reactor than anything we could get
from float zoning. I believe the current slices are on the order of 14"
in diameter.
If I had a good milling machine all of my computers would be running
water cooling.
I had the order made out for a floor mill and a precision lathe laying
on my desk ready to send. I was procrastinating for a week or two and
that's when the dot com bubble burst. I never did get the lathe and mill.
73
Roger (K8RI)
> 73,
> Gerald K5GW
>
>
>
>
> In a message dated 5/16/2008 2:18:42 P.M. Central Daylight Time,
> sub1@rogerhalstead.com writes:
>
> F. Veitch wrote:
>
> I used and have worked with water cooled amps and oscillators for
> years. We used De Ionized (DI) water for years with systems up to
> multi-hundred KW. Either DI or distilled water should work fine.
> Most
> tap water is far too conductive. Just put your ohm meter on the high
> scale and stick the probes in a half inch to one inch apart. As
> long as
> it shows 50-100K it should be fine. I used a probe that had 1 CM
> square plates separated by 1 CM to measure Ohms per cubic CM , or
> resistivity.
>
> The only thing to remember about DI and Distilled water is they are
> corrosive to copper and brass. However the amount of flow in
> intermittent amateur service should show no degradation in years of
> use. You might need to replace the water every now and then as it
> picks
> up ions from the metal in the system. Others have commented on
> how they
> monitor this. If there are no indications of lower conductivity
> there
> is no need to replace the water. In systems that ran almost
> steady 24
> X 7 we had to replace copper and particularly brass fittings every
> 3 or
> 4 years. Based on that I'd expect the normal amateur system to
> last a
> lifetime. Water replacement which was around a thousand gallons was
> about twice a year, but it ran through a lot of equipment and in an
> industrial environment. I'd hate to tell all the stuff that went
> into
> that, but a half a salt shaker in a thousand gallons shut the whole
> system down. That was expensive in the 100's of thousands of dollar
> range, but we never did find out who did it we were fairly
> certain. Just
> rumors from the crews running all that equipment. Word was someone
> remarked, "I never thought that little would do that much". <:-))
>
> Look into "Vapor Phase" cooling as well.
>
> 73
>
> And good luck,
>
> Roger (K8RI)
> > I am in the process of getting a water cooled GS-15B cavity on
> line and I
> > wonder if the group has any recommendations on coolants.
> Distilled water is
> > typically of unknown provence, so you are never sure if it is
> really low
> > conductivity unless you measure it. Somehow the idea of
> 1700-2000V on water
> > of unknown conductivity just bothers me. (silly me!) I have
> heard that some
> > Radar systems and high power lasers use a special ethylene
> glycol for a
> > coolant. I wonder if anyone in the group has any experience
> with such
> > coolants and if they can recommend a source for same.
> >
> > Thanks and regards
> > Fletch
> > K3JYD
> > FM18
> >
> > _______________________________________________
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> >
> >
>
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