[Amps] FW: Fan sounds like F-15

[Gary Smith]

The old Alpha I picked up last year was owned by a smoker. The fuzzy 
paint of the original cabinet was replaced by newer, enamel paint and 
when I got it home I notice how much remarkably louder the fan was 
than the one in my AL-1500. I disassembled the as-new chassis to find 
to my horror, nicotine stains throughout. I had to remove the tar & 
dust that had accumulated on all the components & chassis (a week 
long effort to do it right BTW). In the process I noticed the blades 
on the squirrel cage fan had by far the worst accumulation of crap 
which Makes sense, they were the moving parts and designed to grab 
the air so they had tar and dust thoroughly embedded on the blades & 
into the corners where the blades meet the flat walls of the turbine. 
This is what it looked like with that crap on it:
http://doctorgary.net/fan.jpg
There was no rust in it, that was accumulated crap.

I removed the fan and saw there was a balancer on one of the blades 
just like a weight on a tire & got to thinking that accumulation of 
crap would have to create turbulence & turbulence is what creates 
sound. Think of a Dr. using a stethoscope. I cleaned the fan, 
replaced it and discovered the sound was to me, cut by maybe 1/2 of 
what it was when I got home. If not in dB, the character of the sound 
was smoother as it should be. 

I was emailing someone about the amp a couple of weeks ago and 
decided to revisit the fan and looked at it carefully again and 
noticed the outside where the air was not being grabbed was shiny 
clean but the inside of the blades was a different color & 
characteristic & I realized I hadn't cleaned those blades off down to 
the shiny metal but had just removed the loose accumulation of crap 
that had easily come off with Q-tips soaked in denatured alcohol. So 
I got obsessive about cleaning it & soaked it in denatured alcohol 
for an hour or so & then used a dremel with a long thin white buffing 
pad to go after the inner parts of the blades & cleaned them down to 
the true metal surface. In the process discovered there were little 
burs from the manufacturing process on the blades where they had been 
created by some kind of punch, more turbulence... I used a file to 
file the burs flat & then for grins, rounded off the cutting edge of 
the blades with some #400 wet/dry paper so it might could be a bit 
more "aerodynamic".

Do doubt doing all this was overkill but I wanted to see if there was 
any difference in what I could hear and the answer is absolutely yes. 
That final bit of obsessiveness smoothed out even more the sound and 
now it is more of a blowing sound, and not a distracting noise. I 
should have taken a photo of the fan afterward but didn't think of 
it, not that it matters, you get the idea.

Just my observations of before & after. YMMV.

Gary
KA1J


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