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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