[Amps] Coupling a blower to an air system socket

[Carl]

If youre building from scratch then Id think you would make the effort to 
accomodate the cooling system from the beginning. Use a subchassis for the 
tube that is easily pressurized (Ameritron will sell you several types and 
the blower that mates to them) or construct internal walls in a large 
chassis; companies sell those parts. Then mount the blower on the rear of 
the main chassis.

If a duct is required then "Shop Vac" hoses or dryer ducts can be used. I 
use a large Shop Vac hose to cool a military surplus 432 mHz cavity amp and 
fabricated a small box  to transition from the hose to the cavity air inlet. 
The hose is very flexible and allows the blower to be conveniently mounted 
so that air is drawn over the PS and control circuitry. The cavity inlet air 
is barely warm and the 2750W Pd tube is only running 1200W out (If I cranked 
it up my feedline and antenna would melt) so everything runs comfortable.

Ductwork has air resistance so use as short a length as possible unless the 
blower has sufficient capacity.

Carl


----- Original Message ----- 

>   I believe the air system socket connected to a duct is especially useful 
> when
> you can't have a pressurized cabinet. There are situations where large 
> cabinets
> are used and sealing them is not possible.
>
> 73
> Bill wa4lav
>
> At 09:04 PM 3/15/2013 -0400, 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.
>>--
>>   Ron  KA4INM - Youvan's corollary:
>>                 Every action results in unwanted side effects.
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>
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