Mr. Clements description of the cooling of the 3-500Z tubes is exactly what
occurs in the HF-2000. We also get cooling air on the base of the tube. Use
of the caps on the tubes is open to debate. My experience for light duty SSB
and CW use has found they are not required. The primary objective of the
HF-2000 is to provide a legal limit amplifier that is almost whisper quite.
This has been achieved. If you want to run the HF-2000 in a high duty cycle
mode, we recommend an external muffin fan (50 CFM) be placed on top of the
amplifer directly above the tubes. This provides the necessary cooling for
high duty cycle.
73's
Ray C. KB8VU
QRO Technologies, Inc. http://www.qrotec.com
-----Original Message-----
From: Phil Clements <philk5pc@connect.net>
To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: Friday, April 24, 1998 11:55 AM
Subject: [AMPS] Re: Cooling of Tubes
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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