Re: [Amps] re cooling of coils

[W0UN -- John Brosnahan <shr@swtexas.net>]

> The cure for that is to add the optional Muffin-type fan on the air inlet. 
> It doesn't increase the total airflow much - its main purpose is to make 
> the incoming air very turbulent, so the transformer is cooled much more 
> *efficiently* (along with most of the other components on the power-supply 
> side). But the price for that is a noisy fan, right onto the rear of the 
> amp where you can hear it.
>
> I don't know what type of fan they supply, but low-noise Muffin-type fans 
> are available that are at least 10dB quieter than the regular type.


RE: QUIET MUFFIN FANS

Ian--

Couldn't agree more with what you say with one exception.  The optional muffin
fan that was available from ETO for the Alpha 87A (and other models) during
most of the 1990s WAS a very noisy fan.  And many hams opted to install
a locally obtained, flea-market fan.  These were either noisy if they moved
a lot of air or very quiet but ineffective at moving any air into 
back-pressure.

When I took over as president I went on a quest to find the ultimate muffin
fan that moved a lot of air, worked reasonably well into back-pressure,
and was as quiet as possible.  I found ONE fan that met my needs and
in fact it was about 10dB or more quieter.  And this is the fan that was
supplied by Alpha from about 1999 on.  Although I cannot speak for Alpha
amplifiers now that the company is owned by Crosslink, I assume that they
have continued to supply this "good" fan.

This fan was chosen to provide good, turbulent air flow around the transformer
as well as to reduce the actual exhaust air temperature, providing 
increased cooling
for the expensive 3CX800A7s.  During heavy contesting I have noted typically
10 or more degrees (F) reduction in air temp out the tube chimneys--as measure
outside the amp but directly in the air path.

The fan I chose was the Pabst 4580Z and it provided a great improvement for
ambient noise in the shack.  To the point where some of my computers made
more noise than the amp.  But that is another story.

I highly recommend the Pabst 4580Z muffin fan.  Typically NOT something
you will find at a flea market sale--but well worth the price of a new one.
I believe Newark (in the US) still stocks them.

73--John    WØUN



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