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[Amps] water purity/conductivity in water cooled tube amplifiers

Subject: [Amps] water purity/conductivity in water cooled tube amplifiers
From: Steve Bookout <>
Date: Fri, 13 Apr 2018 21:40:20 -0400
List-post: <>
Hello all,

About 10 years ago, I built two 'boilers' for GS-35b tubes, totally for the heck of it.  To date, I have not actually used either one, as building a new amp was not high on my list of things to do.

In my 'past life, I did R&D, high precision machine work, so this was a bit of fun, to build something different for myself FOR A CHANGE.

My general plan was to use 3/8 inch silicone tubing, to and from, the tube boiler.  In order to give myself some 'dielectric length', I was going to wrap several turns of the tubing around a round form in a single layer.  This would be kind of like coaxial choke some wrap on a piece of PVC.      I think I would rather have 3 or 4 feet of 'series water', than have the HV only 10 inches of water from conductive 'stuff'.

Plan on putting a micro ammeter from a metal water fitting  to chassis in order to measure the conductivity from the water to chassis, at some point in the water circuit.

I know that really pure water is actually corrosive and will do it's best to gain ions in order to get to some natural level of minerals/contaminants.    I built the coolers out of several pieces of brass and hard silver brazed it all together.  I know the electrical current will cause an etching or eroding effect of the materials in the cooler, but I used what I had.   At this point, I have no idea how often I will changing  out the water.  Could be after only 10 hours of use, or it may be 100 hours and the cooler may rot out in no time.

So, I need to know what the 'big boys' do in industry.  At what point, in uS/cm, do I change out the water? The metering of the water conductivity would be measure 3 or 4 feet from the tube boiler (@ 3600 volts)  How many inches (feet) of 3/8 inch dia distilled/low ion water, in silicon tubing, do I need to have between 3600 volts and gnd (thru a meter?)

This will all be in a rack cabinet, where space is not going to be an issue.  Already, mocked up the cooling, with the boiler sitting flat in an electric skillet on high, with water flowing to an aluminum transmission cooler, being pumped by a 110 gal/hr submersible aquarium pump.   After 1/2 hour, the in > out temp difference was only 2 degrees, so that is looking good.

I was thinking about the small contact area between the tube 'stem' and the water cooler.  For those not familiar with the GS-35b tube, the large copper cooler, is attached to the tube body (plate) with a tapered 'stem' of a few degrees. ( I measured it with precision equipment and fitted it as it should be fitted, but I just don't remember the actual angle -- 2 degrees/5 minutes sounds familiar...)   I was wondering if a thin coat of 'Arctic Silver', or some other heat transfer compound used for CPU's, would be a good thing.

3600 volts on the plate.

Would love to hear comments about any of this.  None of this is fixed in 'stone'.  Just my general plans.

73 de Steve, NR4M
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