[Amps] Coupling a blower to an air system socket

[Pete Smith N4ZR]

I *think* I have read (here?) that there is a big difference between the 
physics of pressurized and unpressurized systems in this respect.  Is 
there anyone out there who understands this and can comment?

73, Pete N4ZR
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On 3/15/2013 9:04 PM, KA4INM wrote:
> On 03/15/13 16:58, Alan Ibbetson wrote:
>
>> For minimum airflow resistance for a forced air cooled amplifier it
>> would seem the blower needs to discharge in a straight line directly
>> into the underside of the valve socket. This leads to a fairly tall
>> structure with the blower underneath the RF deck.
>
>> What is the "right" way to make the physical connection between blower
>> and air system socket? Rigid ducting? Something resilient like rubber?
>> Or (what intrigues me) how about a fabric transition duct as shown in
>> several places here
>
>> http://users.pipeline.com.au/~burst/stc.htm
>
>> The "floppy" fabric seems attractive as a way to take up minor (major?)
>> misalignment between the blower and RF deck if they are built as
>> separate units and should help isolate any blower vibration. A competent
>> seamstress (seam-master) would be able to take differences in duct shape
>> and size in their stride too.
>
>> Has anyone got a feel for the pros and cons of the use of fabric rather
>> than more rigid blower couplings?
>
>   I should think the difference is negligible and not worth the bother.
> Many successful amplifiers using all kinds of air cooled tubes have 
> been built with the system where they are simply pressurizing the box 
> under the tube/s with the air passing through or around the tube/s above.