Re: [Amps] muffin fans

["Ian White, G3SEK" <G3SEK@ifwtech.co.uk>]

Partain, Chuck wrote:
> anyone ever do any studies about muffin fans for cooling BIG tubes?
> I have a decent size blower I'm going to use on my amp (gu-84b) and wondered
> if there was a smaller fan (I'm into the size reduction mode now) to use.
> they indicate ~60cfm at 30mm H2O across the tube. I have a squirrel cage
> that's going to work but would pay for a quieter smaller hi performance fan
> to do the trick. Looked around and see a lot of CFM measurements but not
> including the pressure.

That's because muffin-type fans have very poor performance against the 
kind of back-pressure created by the anode cooler of a ceramic tube. 
They are good for delivering high volume of air when the back-pressure 
is low, but any small back-pressure will decrease the CFM by a *lot*.

The rated CFM figure is always against zero back-pressure ("free 
discharge"). In other words, it's a theoretical maximum value that 
you'll never see in practice.

Squirrel-cage blowers have several features designed to develop pressure 
as well as deliver volume, so that's what you're going to need.


--
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)

http://www.ifwtech.co.uk/g3sek
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