[Amps] re cooling of coils

[Ian White, G3SEK]

W0UN -- John Brosnahan wrote:
>
>>
>>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.

Papst certainly has a range of "low noise" and "super low noise" fans, 
and numbers of other manufacturers supply near-equivalents.

However, the quieter models also have a lower air flow rate, and it's 
vital to avoid installing a fan that has a lower flow rate than the main 
blower - the fan would then be choking the airflow instead of boosting 
it.

At least Alpha owners now know exactly which one to pick.

At a flea market, the quieter fans are generally recognisable by having 
blades with curved edges and rounded-off corners, but I've no idea how 
to tell "quiet" from "super quiet" without a catalog.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek