To: <amps@contesting.com>
>Date: Fri, 24 Apr 1998 10:56:33
>To: Jon Ogden <jono@webspun.com>
>From: Phil Clements <philk5pc@connect.net>
>Subject: Re: Cooling of Tubes
>
>At 10:19 AM 4/24/98 -0500, you wrote:
>>>>Yes, that bothered me, too. QRO claims the single fan at the end of
>>>>the tube compartment pressurizes the entire space and provides
>>>>adequate
>>>>air flow to cool both tubes in SSB or CW service.
>>
>>Pardon my ignorance, but from my limited knowledge of thermodynamics,
>>moving air provides cooling, static air does not. So just because there
>>is pressure and "some" moving air, that doesn't seem to necessarily cool
>>it. Direct air flow over a tube is a far better cooling solution than
>>just air flow in an entire cabinet.
>>
>>I would definitely add additional cooling fans to this unit if it was in
>>my shack.
>
>Rich, AG6K pointed out in an earlier post the ingenious method used by
>Heath in cooling 2 entire 3-500Z tubes using only one muffin fan.
>Although the fan in the Heath is placed broadside to the tubes, the
>same principals would apply to the QRO system where the tubes are lined
>up single file behind the fan. The amount of cooling air for the second
>tube is almost the same as that available for the first one, less the
>friction loss caused by the first tube's glass envelope. The airflow
>follows the contour of the tube envelopes somewhat like the flow
>around an aircraft wing in flight. Perform a simple test...take an
>electric hair dryer, point it directly at your nose, about 2-3 inches
>away from it. Note the airflow and hot air all the way around your head;
>even the back of your neck. If QRO did their engineering homework, they
>would have determined by the paint test that both tubes stayed within
>a few degrees of each other while in operation. I have not examined
>the QRO line of amps that closely, but if they, unlike Heath did not
>provide cooling air for the tube base and pins, this could lead to
>a melt-down in the future. Also the omission of air system plate caps
>was not a good idea. Before I redesigned or added additional cooling
>I would invest in some of that temp. sensitive paint to see if both
>tubes, from top to bottom are within mfg. specs. At first glance at
>a SB-220, one would think that the cooling of the tubes might be a
>bit under-engineered, but quite the contrary is true....
>
>(((73)))
>
Phil, K5PC
"To do is to be".....Sartre
"To be is to do".....Aristotle
"To be or not to be".Shakespeare
"Do be do be do".....Sinatra
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