[AMPS] RF deck cooling

[Ian White, G3SEK]

G SEVEN wrote:
>
>Has any one tried using a blower from the top of the deck through to the
>bottom. I have a small 19" rack RF deck with a 2-1/2" bottom, and my blower
>has a 3" opening. I am trying to mount the blower on the back of the amp, I
>dont want to mount it on the bottom because I would like to be able to set
>the deck on a table. So I was thinking of trying to pressurize the top of
>the deck and have the air flow down to the bottom and out.  

Blowing into the output compartment is standard practice on many VHF/UHF
cavity amps that use "external anode" tubes - but not quite in the way
you were thinking of doing it.

If you can totally seal and pressurize the output compartment, then you
can duct the air hot out through the anode cooler and upward through a
chimney. (The normal chimney between the base and the anode cooler is
not used.) Besides the anode cooler, the only other exit from the output
compartment must be downward around the base - perhaps 30% of the total
air flow should go down that way.

This arrangement puts the air-flow paths for the anode and for the base
"in parallel", so the pressure drop is lower than the conventional mode
where the two are "in series". This allows most blowers to generate
significantly more volume flow rate, so the cooling is generally better.

You can measure the volume flow rates quite easily by timing how long it
takes to blow up a light plastic bag (tnx K6GT). 


>Would this work
>if I doubled up on the blowers and used two instead of one?
>
No need... so long as you can seal and pressurize the output
compartment. 

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.com/g3sek

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