[Amps] muffin fans

[R.Measures]

>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.
>
**  For even more pressure, use a radial-wheel centrifugal blower.