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Author Topic: SB-220 fan  (Read 1098 times)
KC8RPD
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Posts: 134




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« on: December 30, 2016, 05:19:28 PM »

I'm going over an SB-220 or 221 that I acquired a while ago.  While I'll be replacing a few things as a matter of course- HV filter caps and such- I keep looking at that cooling fan and wonder if a boxer (muffin?) fan might be more effective.  I have a selection of these things, 4" & 5", so I have choices.  I figured this has been done before, so I thought to ask.

Thanks in advance

Rich
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N4UE
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Posts: 657




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« Reply #1 on: December 30, 2016, 05:28:18 PM »

Hi Rich. The Heath engineers did an excellent job with the 220  I just finished a complete rebuild of a 220 and my fan was fine. If yours is binding or has other problems, Harbach sells a replacement.
I also added a 'shroud' both above and below the chassis. The fan (in addition to cooling the tubes) provides cooling to the tube pins, which is important.

I have an LK-500 I recently converted to 6M. It has a large muffin fan which also cools above and below the tube sub-chassis. But, that fan is pretty loud. The Heath fan is great.

You can find pictures of the shroud on the web.

ron
N4UE
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WA7PRC
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Posts: 1713


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« Reply #2 on: December 30, 2016, 07:23:03 PM »

I agree with Ron N4UE. Richard Measures AG6K has written about the SB-220/1, including cooling (link). As well, others have mentioned that it works fine as long as you ensure the fan is installed as the manual states, the blank plate on top is in place, and the motor is maintained. If the motor bearings are shot, you can buy a replacement motor from Grainger, Dayton pn 4M070 (link) for about half what a certain popular HK aftermarket supplier gets.

The 3-500Z tube specifications (datasheet) state that the wire-glass seals must be maintained below 225°C (anode) and below 200°C (filament). That is why the fan blade protrudes below chassis level. David K5DBX found that adding a shroud around the OEM fan blade increased the air volume and decreased the fan blade noise. This is my version:

I used thin soft aluminum strips, about 1-1/2" wide. Existing hardware secures it, as well as a bead of RTV. Not shown is the strip BELOW chassis level.

Bryan WA7PRC
http://www.tinyurl.com/wa7prc-sb220
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KC8RPD
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Posts: 134




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« Reply #3 on: December 31, 2016, 05:14:36 AM »

Thanks to all for the info.  The shroud is something I had thought of as well.  It is said that a shroud can increase efficiency by up to 30%.  I hope my work looks as good as the example.

Rich

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