The solid top cover piece and the proper positioning of the fan blade in the
baffle certainly does direct the flow.
Properly built and knowing how to solder the filament socket wires does
wonders for a SB-220. Its a great design that does what it is supposed to.
Unfortunately a small percentage of builders cant do either and come up with
all sorts of excuses to show their ignorance. With over 300 220's converted
to 6M Ive seen them all.
Carl
KM1H
----- Original Message -----
From: "Mitch Cox" <ww4cox@embarqmail.com>
To: "Amps" <amps@contesting.com>
Sent: Saturday, December 18, 2010 1:20 PM
Subject: [Amps] Fw: Fan for SB220
>
> ----- 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
> >>>
> >>>
> >>> _______________________________________________
> >>> 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
> >>
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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