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Author Topic: Amplifier Fan Noise  (Read 10758 times)
VK4DD
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Posts: 79




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« Reply #30 on: January 02, 2012, 06:30:48 PM »

Hi

I wonder has any one played with water cooling. Is it great or is it just an other can of worms with lots of corrosion and maintenance issues.? Do you use water or other liquids because of corrosion?

73 Ron
VK4DD
 
« Last Edit: January 02, 2012, 06:32:36 PM by VK4DD » Logged
M0HCN
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Posts: 473




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« Reply #31 on: January 02, 2012, 06:49:58 PM »

Not for amplifiers, but I have watercooled high power DC supplies (Think 60A @ 200V) for laser applications.

Actually the biggest pain is condensation when the feed water is below the dew point, the condensate drips off the cold plate and well there is one much despised implementation that put the control electronics board right below the cold plate..... It used to result in blowing a great many 2N3055 on a boringly regular basis. 

Electrolysis can be an issue if running the water in contact with high voltage, best to run two loops for that with DI water in the primary, but note that DI water is somewhat corrosive. An ion exchange cartridge is important if trying this. If you can keep the water conductivity low enough it does however make a truly excellent insulator. 

In terms of the cold plate, getting sufficient turbulence to avoid boundary layer effects is important for best efficiency, a fairly open coil spring pushed into the cooling channel combined with a reasonably high flow rate helps here. 

Overall, I am not sure it is worth the pain at less then low 10KW levels, above that or is size and weight are critical and you have a suitable chilled water loop already in place, then fine.

Regards, Dan.
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K1BXI
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Posts: 812




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« Reply #32 on: January 02, 2012, 08:24:32 PM »

About 40 years ago Alpha tried it with the PA-70V.  It had vapor phase cooling. It used  a vapor cooled Eimac 3CV1500. I believe that tube had a very short production run. As did the PA-70V.

 A few survived and were converted to use a 3CX1500/8877. A google search on the PA-70V will provide some limited information. 


John
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VK4DD
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Posts: 79




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« Reply #33 on: January 03, 2012, 12:39:26 PM »

Not for amplifiers, but I have watercooled high power DC supplies (Think 60A @ 200V) for laser applications.

Actually the biggest pain is condensation when the feed water is below the dew point, the condensate drips off the cold plate and well there is one much despised implementation that put the control electronics board right below the cold plate..... It used to result in blowing a great many 2N3055 on a boringly regular basis. 

Electrolysis can be an issue if running the water in contact with high voltage, best to run two loops for that with DI water in the primary, but note that DI water is somewhat corrosive. An ion exchange cartridge is important if trying this. If you can keep the water conductivity low enough it does however make a truly excellent insulator. 

In terms of the cold plate, getting sufficient turbulence to avoid boundary layer effects is important for best efficiency, a fairly open coil spring pushed into the cooling channel combined with a reasonably high flow rate helps here. 

Overall, I am not sure it is worth the pain at less then low 10KW levels, above that or is size and weight are critical and you have a suitable chilled water loop already in place, then fine.

Regards, Dan.


Gee TNX Dan sounds like something to avoid. Is there any merit in using these radiator coolants? I suppose the dew problem in humid climates will still exist.

Also interesting reading about this vapor cooling. TNX John.

73 Ron.
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M0HCN
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Posts: 473




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« Reply #34 on: January 03, 2012, 01:06:29 PM »

If you can arrange the cold plate to be grounded and use some magnesium or zinc anodes to control the corrosion then water can work, the condensation issue still exists of course.

IIRC There was a version of some of the external anode tubes made with a BeO block and mounting plate precisely so as to enable water cooling, and I seem to remember something similar for the small UHF power tubes, I still say it is a major pain in the tail however (Especially the UHF variant which ran water directly over the anode structure, DI was a must).

Phase change cooling is efficient and has the nice feature that it maintains constant temperature as the boiling point of the coolant (at any given atmospheric pressure) is constant, but I seem to recall some problem the BBC shortwave services had with a very cold winter and freezing the condensers.

All these methods have their issues, and it is only when power becomes large that the benefits outweigh the pain.

Regards, Dan.
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VK4DD
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Posts: 79




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« Reply #35 on: January 03, 2012, 02:06:05 PM »


Phase change cooling is efficient and has the nice feature that it maintains constant temperature as the boiling point of the coolant (at any given atmospheric pressure) is constant, but I seem to recall some problem the BBC shortwave services had with a very cold winter and freezing the condensers.

All these methods have their issues, and it is only when power becomes large that the benefits outweigh the pain.

Regards, Dan.

Fair dinkum may be that's why a lot of these broadcasts are now being done from warmer countries, some EU countries transmit from Madagaskar, nice and warm and no freezing temperatures. I suppose you would not get a lot of that extreme WX is rare these days in the UK. Or the remedy would be is to keep the TX running so that the water would not cool down.

So even when you have a commercial high end TX you can still have problems. I guess there is always something which can be made better. Home brew isn;t any different.

TNX leaned heaps, no water cooling for me. It makes you wonder how many over  computer over clockers ruined their mother boards with condensation etc.

73 Ron.
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M0HCN
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Posts: 473




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« Reply #36 on: January 03, 2012, 03:20:49 PM »

Plenty I suspect, but all they will tell you is how much past specifications they can run the chip, and that it "Hardly ever crashes".....
Not really what I consider to be good engineering.

Regards, Dan.
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VE7RF
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Posts: 212




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« Reply #37 on: January 03, 2012, 11:10:57 PM »

Plenty I suspect, but all they will tell you is how much past specifications they can run the chip, and that it "Hardly ever crashes".....
Not really what I consider to be good engineering.

Regards, Dan.


##  per eimacs "care and feeding" [old paper copy]  Forced air will remove 50watts per sq CM of anode area. Vapour phase cooling will remove 135 watts  per sq CM.    Water will remove 1000 watts per sq cm. If you look at all charts etc in the care and feeding [ "nukiyama's  theory of boiling water] you will see that vapour phase works best at 135 deg C..and not 100 deg C.  [That whole section got blown out on the new on line care + feeding].  At the telco I worked at for 34 years, at one site, it used vapour phase cooling for the emegency diesel generator.  No radiator required at all.  It was a pita to maintain though. It was made by BMC in the uk. It was replaced by a larger, more conventional unit.

## If you read in VO Stokes book [ UK book on high power amplifiers] they highly suggest to avoid water and or vapour phase cooling like the plague...and stick with air cooling, it's a lot simpler.  All that heat from the water cooling has to be pumped to an external rad, then air cooled anyway. [the rad]. So the heat all has to be ultimately transfered to the air eventually.

##  Lot simpler to either just locate the noisy amp to another room, where it belongs, or remote the blower, and pipe the air in via dryer hose.

later...Jim  VE7RF 
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