[Amps] Cheap auxiliary amp cooling

[Bob K6UJ]

Jim,

Sounds good.  I added a computer fan to my Alpha 76CA also.
The air inlet vent holes are on the back of the amp so I bolted the 
fan over the inlet.  It looks like the original design. 
I used a Radio Shack 273-241C, 4", 65CFM, 120VAC fan. The Radio Shack fan is
very quiet and even runs slower because I used the 95VAC supplied at the 76CA blower terminals.
The amp now runs cool with no heat build up.  I can't tell any increase of noise from the fan addition 
at all. 

73,
Bob
K6UJ





On Mar 30, 2012, at 12:29 AM, Jim Barber wrote:

> 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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