> On Wed, 6 Dec 2000 09:48:45 -0600 , Brakob, Hans wrote:
>
> >Just installed a new AL-1200 yesterday.
> >The blower is kinda loud, like sitting in the back row of a DC-9 with
> >full reverse thrusters. I notice the blower has wiring options for 4
> >speeds (it comes wired for 3rd gear). Has anyone rewired for lower speeds
> >and used the amp for contesting?
The AL1200, because of complaints like yours, had the blower
speed reduced about 12 years ago. If you want to use the amp
really HD, you need to speed the blower up a bit.
That blower cost over $100, and is the most quiet blower available
for the static pressure and airflow out of dozens of blowers tested.
If you want to reduce noise, you can put sound deflectors over the
outlet and inlet vents, as long as you maintain 1" of air space to
the cabinet. A three sided box with the inlet facing down for the
intake and reward for the exhaust works fine. That's what I use here
but I also use the high-speed blower.
> I can only offer some advice if you're planning on using the AL-1200
> for RTTY. I had one several years ago and smoked the 80/160 tank coil
> twice while RTTY contesting. IOW, the AL-1200 cooling is marginal for
> full-power, full-carrier operation. I'd be careful about reducing the fan
> speed. After replacing the tank coil, I held it to less than 1 kW out and
> had no problems.
Right you are. Because people somehow expect you can move a
room-full of air in a few minutes without making noise, the blower
was sized as marginally as possible and still allow CW and SSB
full duty operation. That places the blower too small for RTTY.
> The problem is that the exhaust air from the tube is dumped into the
> cabinet rather than being vented outside. I would strongly recommend
> modifying it to vent air outside, although this would probably void your
> warranty.
That won't help a bit, especially in units less than three years old
that have additional vents that blow a bit of air forward near the floor
of the cabinet under the tank. The air coming up out of the tube is
pretty well straightened by the fins of the tube, and adding a full
chimney just barely makes a difference in that.
The largest cooling addition you can make, besides adding the
high speed blower (which is about 10 dB louder), is adding a high
speed muffin fan to the inlet and pressurizing the air inlet. That fan
must be at least an 80 CFM fan, and produce .05 inch or more
static pressure at the inlet.
For normal CW or SSB contesting the stock blower is generally
fine, if run on the highest speed. Many contesting stations have a
shack full of unmodified AL-1200's, like KC1XX and others.
Bottom line is if you want a cool running amp on your desk with
over 1500 watts of heat to remove, you either have to put up with
the noise or else run QRP.
73, Tom W8JI
w8ji@contesting.com
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