[R-390] Alternative to IERC tube shields?

[John Vendely]

When noise is a primary concern and a modest volume of air suffices, a 
simple expedient is running a 220VAC muffin fan at 110V.  It's simpler and 
more efficient than the cumbersome "solution" of a dropping resistor, which 
adds heat when you least want it.  It's quiet, and in many situations even a 
small airflow will provide a worthwhile temperature reduction.   One 
occasionally encounters a fan which simply won't run at such reduced 
voltage, but in most cases, it's no problem.  I've employed this simple 
trick on several occasions with adequate results.

73,

John K9WT

----- Original Message ----- 
From: "2002tii" <bmw2002tii at nerdshack.com>
To: <R-390 at mailman.qth.net>
Sent: Monday, August 17, 2009 12:16 PM
Subject: Re: [R-390] Alternative to IERC tube shields?


> Bob wrote:
>
>>And while I haven't done any testing to prove it, I would
>>think that adding a bit of forced convection cooling would help a lot.
>>Thanks to cheap and quiet brushless muffin-type fans it is easy to try
>>at least.
>
> Definitely a big improvement.  But where do you find these "quiet
> brushless fans"?  I guess quiet is in the ear of the behearer.  In my
> view, all the cooling fans I've ever met are "quiet" only when
> evaluated in a small room with a window air conditioner running.  I
> generally use oversize fans and slow them way down to reduce the noise.
>
> A noiseless option is to build a chimney about 3-6 feet tall (~ 1-2
> meters for the metrically inclined) that is fed from vents in the top
> or top-sides of the radio, leaving appropriate bottom and/or
> bottom-side vents for air intake.  Give thought to the
> convection-driven air circulation.  Sometimes, one needs to block off
> some vents and/or make some new ones.  Typically, the chimney for a
> 390 or SP-600 would be 30-40 square inches in cross-section.  I build
> them out of corrugated box cardboard, with shallow pyramidal
> transitional sections. You'd be amazed by how much air such a thing can 
> move.
>
> Best regards,
>
> Don
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