While playing with my new toy, (QRO HF2500DX) I found that I was able to
confirm that it does indeed need auxiliary cooling for high duty cycle
modes. Even at relatively low or no power output - just the ZSAC is
450ma @ 2400V, or over 1000 watts of just plain old heat.
I decided to check my computer parts supplier to see if there was
anything that looked like it might work for a "booster" exhaust fan, and
it turned out that a 250mm (10"!) 12V PC case fan has a brushless (no RF
noise) DC motor, turns slow and makes little audible noise, but manages
to move 105 CFM of air. (at zero back pressure, of course) They cost
$26.99 USD in single units.
I haven't built a sealed mount yet, but just sitting the fan on top of
the case above the tubes dropped the exhaust temp 40-50F during
375/1500-watt AM transmissions. The noise of the "booster" fan is so low
compared to the internal 50CFM blower that I can't really hear it.
Legal-limit SSB conversations (with modest compression) get the
airstream only lukewarm now, instead of 130F+ .
I also bought a 243 CFM 8" 12VDC Conair-Rotron hurricane generator that
I want to build a temperature-ramped PWM controller for when I get A
Round Tuit. (probably 25khz, 30-100% duty cycle to copy the newer PC
controllers, which work well) In the meantime, the cheap PC case fan
seems to be getting the job done.
73,
Jim N7CXI
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