Anything that comes in contact with distilled water is a potential
contaminate, including: air, tubing material, metalized heat transfer
condensers, couplers, even copper plating on the inside of a tube boiler or
SS amp copper heat sink. By studying these materials, the level of
contamination can be kept to a minimum -- to the point where build-up is not
a concern. Early literature tells us to keep contact away from various
material like brass fittings.
Fortunately, vapor phase cooling lends itself nicely to the concept of "self
distillation." In the case of a vacuum tube's boiler, contaminates are
deposited inside the bottom of the boiler and largely stay there unless
perturbed by a tube removal. I've mentioned before that the #1 contaminate
with my vapor amp is mold and mildew build-up. Despite efforts to keep
humidity levels down in my Florida shack, it's just a matter time before
mold builds. Fortunately, I don't see this occurring at intervals less than
about 12 months.
At least in the case of simple vapor-phase cooling, the system cannot be
completely closed as it typically is with liquid water-cooling. A vent tube
is needed to ensure that the boiler pressure does not build, which raises
the boiling point temperature. But venting also allows exposure to the
ambient air, and over time, can result in mold and mildew build-up -- and
that quickly increases HV leakage current.
Jim's experiment is a good one where he used his DMM probes to check for
differences between distilled and tap water. I once found this out the hard
way. A local Walgreens had a sale on "distilled" water under their own
generic brand. So, I purchased a gallon. When I went to purge and fill
water in my Alpha 70V, the leakage meter pegged off-scale. I had never seen
this occur so I thought perhaps the circuit had become defective. But on a
hunch, the system was purged/filled a few times, then filled with
ZephyrHills-branded water. After filling, leakage was once again extremely
low. Lesson learned: stay clear of un-branded distilled water.
Once the system starts clean, it stays that way for a long time. If I lived
in Arizona or New Mexico, who knows...it may be possible to go years without
purging since self-distillation would take care of other contaminates.
Paul, W9AC
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Big Don
Sent: Tuesday, February 21, 2017 10:27 AM
To: Jim Thomson <jim.thom@telus.net>
Cc: amps@contesting.com
Subject: Re: [Amps] SS amps watercooling - was PowerGenius XL
Might run another experiment to see how conductive initially distilled water
becomes after spraying it onto the inside of a cabinet, and on some circuit
boards. Collect the drainage in a pan, which now contains any impurities
picked up along the way, and check the conductivity now......
Don N7EF
On Tue, Feb 21, 2017 at 7:22 AM, Jim Thomson <jim.thom@telus.net> wrote:
> Date: Mon, 20 Feb 2017 19:05:27 -0500
> From: "Ray, W4BYG" <w4byg@att.net>
> To: "amps@contesting.com" <amps@contesting.com>
> Subject: Re: [Amps] SS amps watercooling - was PowerGenius XL
>
> FYI: I'm afraid I have to disagree on the statement below about
> distilled water being conductive.
>
> In industrial experiments in the use of distilled water, I found it
> to be very non-conductive. If I recall correctly, it has a measured
> conductivity of 50 to maybe 100 micro-Siemens per centimeter squared.
> That's not much. Pure water becomes conductive only if it becomes
> contaminated with salt like contaminates. For a comparison, seawater
> typically measures in the thousands of micro-Siemens per centimeter
> squared, because of the high salt content.
>
> While working on a clients project to do so, I spent many hours
> attempting to inject RF into water of various solutions. It was very
> difficult in the lab trying to get RF to propagate thru pure water.
> Other more contaminated solutions not so much..
> 73,
> Ray, W4BYG
>
> ## re-read the post. Neither roger nor I said distilled water is
> conductive.
> I got out 2 identical plastic caps, and filled one with new distilled
> water,and
> the 2nd one with tap water from the kitchen sink. Then stuffed the fluke
> 87a
> probes into each one.... dried off between tests. Distilled water
> reads sky high
> resistance... vs tap water. Thats good enough for me. Distilled water
> is dirt cheap
> to buy and would make an excellent coolant for water cooled LDMOS. Dunno
> how often it would have to be changed out. Even if it was every 6 months
> to a year,
> or even far less, who cares. Simple procedure.
>
> Jim VE7RF
>
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>
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