[Elecraft] Thermal control for Q1 / Q2 in KPA100?

Mike Harris mike.harris at horizon.co.fk
Wed Dec 6 10:17:54 EST 2006


G'day,

| The fact that an exhaust fan flow cools objects better than blowing air 
onto
| a surface is a bit counter-intuitive because standing in the downstream 
side
| of a fan feels cooler to the skin - but that is only because of 
evaporation.
| Careful measurement will show that the cooling effectiveness for an 
object
| like a heat sink is more effective by moving the heated air away from 
the
| object.  Getting the heat away is the objective, and blowing on it is 
less
| effective than exhausting the heated air.

Never seen a suction cooled external anode HPA, from single 4CX250's to 
10kW Klystrons.  I've used a small PC fan blowing onto the right hand side 
of the heatsink, front to rear, inclined about 45 degrees.  During 10-12 
hour QRSS beacon runs at 40W o/p the little fan never came on and the 
heatsink was room temperature.

A bladed fan is easy to stall if there is any restriction to throughput.

Regards,

Mike VP8NO 



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