Does the shield increase overall heat build-up inside the amp because it is
absorbing the heat? I had always thought black was a no-no. I see that you
have improved air flow. Maybe that carries it all away. Interesting though.
I have seen that type of separation or compartmental construction in mission
critical equipment through the years. Today a lot of the mission critical
equipment that I see come through (solid state) is built with a very rugged
single piece cast chassis with lots of compartments separated by walls cast
into the chassis and a single circuit board that mates up on top. Around
each isolated part of the circuit board there is a tight mesh type "RF
Gasket" material. When you put the circuit board in all of the sections are
isolated. You then screw the watertight top cover down with lots of high
torque screws placed to evenly distribute the pressure. That is the type
chassis in most police cars now.
I was at the factory (Motorola) and there was a mobile mounted on the roll
bar of an open cab Holland and Holland tractor in the middle of winter. They
explained that they leave it on all year long in the wx as part of the
testing. It just keeps working. The put them on "paint shakers", cold
chambers, high and low altitude chambers and test for vibration and big
shock. This kind of constructions holds up to it. For the display covers,
they place a faceplate looking toward the high ceiling. There is a tube with
BBs that drops on after another for weeks on the clear display to make sure
it will hold up and stay clear. There is a robot that pushes every button
and turns every pot 24 hours a day to simulate 20 years of operation before
parts are finalized. It was fun to see how they do it now. Before that I had
lamented that the days of quality construction were behind us. It is always
interesting to see how the good stuff is made and how they make sure that
things will run "no matter what"/
Sorry to get off-subject of amps a little bit (a lot), but I though it might
interest some of the builders out there.
N9FUT, Sam
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of donroden@hiwaay.net
Sent: Friday, December 17, 2010 10:36 AM
To: amps@contesting.com
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
>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
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