[Elecraft] KPA1500 Cooling

[Paul Christensen]

>"Until it leaks on the LDMOS devices."

Pure water is an insulator.  Leakage becomes a problem when water becomes
contaminated with conductive particles.  This rarely occurs in closed loop
systems that use distilled water when non-contaminating hoses, fittings, and
heat exchangers are used.  My 2KW LDMOS amp uses water cooling in such a
closed system.     

My main amplifier at home is an Alpha PA-70V.  The amp uses an openly-cooled
vapor-phase system.  A pint of distilled water separates 4KV of plate
voltage and chassis ground.  Water is in direct contact with the plate. In
time, air particles do contaminate the water (usually in the form of algae)
and the system must be purged and refilled at annual intervals.  If leakage
exceeds a predetermined amount, the amp faults and shuts down.  

Paul, W9AC