Barry Kirkwood wrote:
>Not that I am likely to try it, but what is the trick with water
>cooling? Is the water non-conductive, or do you isolate it some way.
Pure water is essentially non-conductive, so you only need reasonably
long inlet and outlet leads using plastic tubing. On entry and exit to
the RF deck, these coolant leads pass through grounded metal sections to
electrically isolate the rest of the circuit. The water gradually
becomes more conductive as it dissolves ions out of the various metals
in the circuit, so the usual trick is to have a microammeter in series
with the ground connection to indicate leakage.
There is information in older ARRL handbooks under the N6CA "quarter
kilowatt" amp for 1296MHz, and more in Eimac's "Care & Feeding".
>What about vapour cooling? how that work?
Yes - see "Care & Feeding" if you can get a copy. So-called "vapour
cooling" is generally water in, steam out, so it uses the very high
latent heat of vaporisation to give effective cooling. You're then into
problems of boiler scaling etc... see the DIY central heating newsgroups
:-)
I should add that the only reason amateur microwavers use water cooling
is to squeeze all possible power out of the very small range of
available tubes. As Traian says, the practical limit is often the
instability of output tuning due to thermal expansion of the cavity and
the tube.
HFers can always find a larger air-cooled tube and better ear
protectors...
--
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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