[Amps] Cheap auxiliary amp cooling (clarification)

[Jim Barber]

I received several offline inquiries as to the QRO HF2500DX's 
manufacturer's specified ZSAC. It is indeed supposed to be between 
400-500ma and the amp performs to spec.

73,
Jim N7CXI

...
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