[Moon-net] AIR FLOW 3CX1500

[Pat Barthelow]

Hello Lance, and all,

Great job on your big amps, Lance,  I really like the looks of them.  As I 
understand the specifications, the pressure drop across the tube, doesnt 
change, with cabinet design, it is a function of the tube size and Anode 
cooling fin  geometry, and is measured in a fixture that basically inserts 
the tube anode. chimney,  and socket, inline forming  a cylindrical chamber 
equal to the outer diameter of the anode.  Once you force air through that  
obstruction in the chamber, (the tube) the pressure  drop is basically 
defined for a given CFM,  as the published value.  If you allow other routes 
for the air flow, through the cabinet, leaks, or elsewhere, the overall 
system  pressure drop gets lower, (similar to ohms law for resistance, 
because of parallel paths of airflow) and CFM through the muffin fans may 
stay high,  but the pressure drop and resultant airflow through the tube,  
which is what is important, does not change.  I would be afraid to use the 
muffin fan type blowers, which I believe could not maintain the required  
airflow through the tube anode.  But, you can't argue with success, in your 
case.  I think though,  especially for high duty cycle VHF  use, like JT65 
demands heavier blowers than muffin fans can provide because of the pressure 
drop through the tube.  Perhaps multiple, robust,  muffin fans like your 
design, can do the job.

Best,
73, DX, de Pat AA6EG aa6eg at hotmail.com;
                  Skype:  Sparky599

>From: Lance Collister <w7gj at accessoutwest.com>
>To: Pat Barthelow <aa6eg at hotmail.com>
>CC: duz at wanadoo.fr, Moon-net at list-serv.davidv.net
>Subject: Re: [Moon-net] AIR FLOW 3CX1500
>Date: Fri, 18 Aug 2006 13:16:04 +0000

>Pat Barthelow wrote:
>
>>Philippe:
>>
>>Re heavy duty use of the 3CX 1500  (8877) on 2m, the site:
>>
>>http://www.g8wrb.org/data/Eimac/3CX1500A7.pdf
>>
>>Shows for HF, a minimum of 38 CFM at .6 " Hg  backpressure is required, 
>>with higher values called for at higher frequencies.
>>That is a pretty strong blast of air,  requiring a pretty strong squirrel 
>>cage type blower...Or, If I was building it  here in the US, I might go to 
>>Walmart, and find a cheap, small Shop Vac Vacuum Cleaner and route its 
>>output hose into the amp air plumbing, from some distance, or through the 
>>wall of the shack to minimize in-shack noise.   Good luck...
>>
>>73, DX, de Pat AA6EG aa6eg at hotmail.com;
>>                  Skype:  Sparky599

>>>From: "F1DUZ" <duz at wanadoo.fr>
>>>To: "Moon-net" <Moon-net at list-serv.davidv.net>
>>>Subject: [Moon-net] AIR FLOW 3CX1500
>>>Date: Fri, 18 Aug 2006 10:01:01 -0000
>>>Hi all,
>>>
>>>I would like to use a 3cx1500 on 2m in JT65, what is the minimum air flow 
>>>needed to have a good and safe cooling (in CFM or m3/h ) ?
>>>
>>>Thanks for answer
>>>
>>>best 73 all
>>>Philippe
>>>F1DUZ IN97nj
>>>Philippe Levron
>>>Malvaux
>>>49570 Montjean-sur-Loire
>>>France
>>>duz at wanadoo.fr
>You will be surprised at how much air you can get from a blower if you 
>reduce the back pressure on it.  Here in my shack, I have used high volumne 
>fans to "suck" air out of the top of the tank compartment to reduce the 
>back pressure on the blower and let it really push the cool air through the 
>tube.  Here is a photo of the way I did this on 8877 amps for 2m and 6m:
>
>http://www.bigskyspaces.com/w7gj/W7GJ8877AMPS.jpg
>
>GL and VY 73, Lance

>Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
>P.O. Box 73
>Frenchtown, MT  59834  USA
>QTH: DN27UB
>TEL: (406) 626-5728
>URL: http://www.bigskyspaces.com/w7gj
>2m DXCC #11/6m DXCC #815