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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>>
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>>
>
>
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