John Lyles jtml at losalamos.com
Fri Mar 10 16:54:47 EST 2017

Eimac has an app note for water and vapor cooling, which is similar to 
RCA/Burle/Photonis and Thompson/Thales, Amperex/Philips, E2V, Siemens, 
Telefunken recomendations. All refer to using DI water (or distilled) 
and resin beds to regenerate the pure water in a side loop. The 
resistivity requirement is such as to minimize DC current in the pipes 
and hoses through the water. By minimize, it is preferred to keep 
current below 1 MA, preferably in the hundreds of microamperes, for the 
highest plate voltage operated. It is up to the designer to select the 
hose diameter to get the proper flow (at min back pressure) and to then 
get the current in the ballpark, but selecting the hose length and the 
worst case resistivity that is going to be tolerated in the design.

Like I have said before, in workplace we comply by selecting hoses up to 
60 inches or longer, and diameters of 1 to 1.5 inch or larger, and 
resistivities of 2 to 5 Megohm-cm. In all cases, we strive to keep 
current in the hoses below 0.5 mA per hose. We get very long life of 
tubes and fittings this way.

Another twist it that the tube manufacturers (for larger tubes) may 
offer a sacrificial electrode that can be installed in each hose at the 
anode end and at the ground end, that will carry all of the current so 
that hose fittings don't erode. These electrodes must be checked 
regularly as they erode away, but the water resistivity can be then 
maintained in the hundreds of kohms-cm instead, a much less expensive 
way. I prefer the former approach. Our resin bottles are replaced every 
6-9 months this way, by calling Culligan man.

Eimac and the others also specify the ph, the oxygen content and the 
dissolved solids level allowed. It is a lot of information that probably 
doesn't apply to the tube cooling that amateurs might require.

It is true that vapor phase cooling is more severe about the water 
purity requirements. Nowadays, modern tubes don't use vapor phase 
exactly, but instead use a form or multiphase coooling, sometimes called 
hypervapotron cooling (by Thales tubes). This is a topic that is beyond 
what hams would use. where the nucleate boiling occurs right in the 
anode jacket but liquid water comes out of the return pipe from the 
anode of the tube. It is much more effective at handling large power 

For solid state amplifier cooling, few of the tube requirements apply. 
This is because the DC voltages are low, like < 50 VDC. In this case 
additives such as corrosion inhibitors and glycols can be used without 
ruining the high resistivity needed for high voltage isolation.

I must state that it is very risky to add anything to an ultra pure 
water system without testing it first for how it will affect the 
resistivity and the rest of water properties. I can furnish a number of 
very good references to the hams wanting to investigate tube water 
cooling. It is recommended to avoid it these days unless you have the 
need to dissipate more than blowers can handle.

> Message: 3
> Date: Tue, 7 Mar 2017 08:03:48 -0600
> From: Joe <nss at mwt.net>
> To: amps at contesting.com
> Subject: Re: [Amps] SS amps watercooling - was PowerGenius XL
> Message-ID: <32059f30-dce3-28b6-0f42-7785a0619c05 at mwt.net>
> Content-Type: text/plain; charset=windows-1252; format=flowed
> In the big Eimac water cooled tubes, what and how did they use liquid
> cooling?
> Joe WB9SBD

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