----- Original Message -----
From: Mitch Cox
To: Mitchell Cox
Sent: Saturday, December 18, 2010 1:08 PM
Subject: Re: [Amps] Fan for SB220
I have never quite understood the premise of painting the inside of an RF deck
ANY color. The black paint part comes from the fact that heat generators that
generate heat from the inside will radiate heat better and more efficiently if
the OUTSIDE is black. For example, a small block Chevrolet engine will run
about 8 degrees cooler if the entire engine is painted flat black as opposed to
the used to be standard, orange. The black surface does an outstanding job of
RADIATING heat. I have witnessed this with an engine on the dyno not painted
running without a thermostat. After the outside of the engine was given a coat
of flat black stove type paint, the temperature did come down between 6 and 8
degrees with no other changes. How this relates to painting the inside of an RF
compartment I am not sure I agree. The inside of the compartment is not
generating any heat so it would seem pointless to paint it. Breaking up the
shiney aluminum and reducing the reflection of heat back to
the tubes may have some merit. The cooling on a standard SB-220 is a hit or
miss proposition at best. You have a large fan blowing at 2 tubes without
anything directing or channeling airflow with a completely open top letting the
purposed airflow from the fan escape right through the roof of the amplifier
before it even reaches the tubes. Then you are counting on a part of the blade
tip to cool the tube seals under the chassis. I have always been amazed the
tubes last in the SB-220 as long as some of them do. Building a shroud to
effectively direct the airflow inside the chassis is a very good idea. Why not
get all of the air on the tubes? Placing muffin fans on top of any amplifier to
help the air escape? This does little more than cool the surrounding metal on
the top of the amplifier and make you think its helping, again the vacuum
created by a muffin fan on top of an amp is drawing air from around it's bottom
and could not possibly reach the tubes underneath unless the
whole top is enclosed and the muffin fan is sealed to the top. It would then
need to vacuum twice the airflow directed at the tubes to keep the muffin fan
from stagnating hot air or creating a log jam of hot air inside the RF deck.
The biggest problem with most amplifiers is the owners sensitivity to a loud
fan. In order to move enough air to keep the tubes cool, there has to be some
noise, then you have operators with all directional microphones that will pick
up a gnat fart in the furtherest corner of the back 40 with everyone
complaining about all the fan noise. Tube cooling is a slippery slope indeed.
From: Gary Smith
To: Carl ; amps@contesting.com
Sent: Saturday, December 18, 2010 12:12 PM
Subject: Re: [Amps] Fan for SB220
This may seem to be to at first but let me go on.
Years ago the same belief existed regarding black vs. sliver on the cylinders
of cast iron Harley -Davison motorcycles. (Yes, I am that old I have seen (and
owned H-D's) with cast iron cylinders.) One school of thought was "paint`em
black, it'll draw the heat out rather than keep it in" The other group's
belief was "paint it silver, that will draw the heat out" and so forth. The
comeuppance was that H-D offered bother colors of paint in touch up cans when
the cylinders got dinged to appease both groups
Pont here is make an aluminum separator and paint it black? Or just leave it
plain finish. Me thinks the difference in temp would not be worth the effort,
Its just a matter of belief.
But as a director of air one way or the other, that's a different subject.
Gary...wa6fgi
----- Original Message -----
From: Carl
To: donroden@hiwaay.net ; amps@contesting.com
Sent: Friday, December 17, 2010 6:33 PM
Subject: Re: [Amps] Fan for SB220
I dont see how that shield helps anything Don, especially black. Have you
done any temperature tests on the tubes and shield? A shroud partially or
fully encloses the fan as in automotive use.
Carl
KM1H
----- Original Message -----
From: <donroden@hiwaay.net>
To: <amps@contesting.com>
Sent: Friday, December 17, 2010 10:36 AM
Subject: Re: [Amps] Fan for SB220
>
> Carl,
>
> I'm supprised no one has mentioned adding a black aluminum shield
> between two 3-500s to help prevent the two tubes from radiating heat (
> and rf ) into each other. I've done this on my SB220, but didn't do
> any IMD measurements. It seems to improve the air flow too.
>
> Don R W4DNR
>
> Quoting Carl <km1h@jeremy.mv.com>:
>
>> Tests have shown that the turbulance from the high speed Harbach does
>> little
>> for the cooling unless a shroud is added. The one saving grace is a WW
>> resistor can be added to reduce the speed a bit and reduce the noise;
>> 150-250 Ohms 20W seems to do well. Dentron and Amp Supply used a
resistor
>> in
>> many of their amps.
>>
>> Carl
>> KM1H
>>
>>
>> ----- Original Message -----
>> From: "David G4FTC" <g4ftc@hotmail.com>
>> To: <amps@contesting.com>
>> Sent: Friday, December 17, 2010 1:47 AM
>> Subject: Re: [Amps] Fan for SB220
>>
>>
>>>
>>>
>>>> A local ham buddy just got back into the hobby after an 8 year hiatus
>>>> and
>>>> got a hold of 2 SB220's. He noticed they run hot and he asked the
>>>> following question...so I figured there are folks out here who might
>>>> know
>>>> the answer
>>>>
>>>> "....see how guys like the Harbach fan kit for the SB220? Mine is
>>>> running
>>>> hot and LOUD. I oiled the
>>>> bearings and cleaned it off of dust, but it's still got to go"
>>>>
>>>> Anyone done this mod?
>>>>
>>>> I recommended a small muffin on top to help extract the hot air for
>>>> now.
>>>> I did it on my old 30L1 and it sure cooled it down.
>>>>
>>>> Thanks
>>>
>>>
>>>
>>> I'm using one of the Harbach fans on a SB220 - they move a lot more air
>>> than the original Heathkit fans.
>>>
>>> Higher air-flow = higher noise
>>>
>>> But I can't say I've noticed that it runs hot.
>>>
>>> Regards
>>>
>>> David G4FTC
>>>
>>>
>>> _______________________________________________
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>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
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>>
>
>
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