Date: Sun, 17 Mar 2013 14:48:02 -0600
From: John Lyles <jtml@losalamos.com>
To: amps@contesting.com
Subject: [Amps] Coupling a blower to an air system socket
Good summary of the actual mechanism of cooling finned anodes in tubes,
Ian. I might mention that hams designing with these tubes should always
consider the air density where they plan to operate their amplifier.
Makes a significant difference if it is going to be 3000 meters up on a
mountaintop or at sea level. Fans must be selected with this in mind.
When I test them with amplifiers, I make a test bench where I run the
blower into a circuit, all the while observing the airflow with
anemometer and pressure meter through a straight laminar flow section.
Then plot the operating point on the fan curves, and see if it is close
to a bad regime. Its best to operate in the zone where a small pressure
change doesn't cause a drastic fluctuation in flow and vice versa. It
helps to have a variable speed blower for the first tests, as you can
optimize your fan speed, noise to get exactly the flow that Eimac or
others want without overblowing with subsequent noise.
73
John
K5PRO
## good point. The tube requires XXX amount of WEIGHT of air
per minute..called mass airflow rate. In denver, the blower has
to put out 20 % more cfm...and also 20 % more pressure. It doesn’t
end there. Blower’s are rated for sea level. More calcs are made...
and the sea level rated blower you choose will be massive, with higher
sea level cfm + pressure ratings than what is required at 5000 feet.
## That is the classic example they used in care and feeding. The you also
have
to factor in the blower inlet temps. Big difference between 10 C and 50 C.
Jim VE7RF
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