Switching Supplies

[williamsonr]

Pardon me if someone has already pointed this out (I have not followed the entire thread)- my past experience with linear supplies reveals an all too often failure mode of either shorted pass transistors or blown control chips (LM-723).  In either case the output voltage from the supply can rise to the unregulated DC filtered voltage (usually 20+ volts) and cook anything attached.  A fast and effective crowbar, if designed correctly, will clamp this voltage before it destroys your expensive equipment. With switchers my experience has been that one or more of the switching FETs or high speed diodes fail and the supply just dies (no output).  Which one would you rather have connected to your brand new K3 if it failed?

73
Rodger
N4NRW
counting down the day till the K3 arrival!
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[WA8EBM]

I  have 2 SEC1223's and no hash. I also have an Astron RS35 and RS50 linear
supplies.  Sometimes the magnetic hum from them drives me crazy.  The little
cork pads Astron puts in them to alleviate this
does not help much. I keep them under the closed console on the floor.
                      Mike  WA8EBM
----- Original Message -----
From: <[hidden email]>
To: <[hidden email]>
Sent: Tuesday, July 08, 2008 6:28 AM
Subject: [Elecraft] Switching Supplies

> Pardon me if someone has already pointed this out (I have not followed the
> entire thread)- my past experience with linear supplies reveals an all too
> often failure mode of either shorted pass transistors or blown control
> chips (LM-723).  In either case the output voltage from the supply can
> rise to the unregulated DC filtered voltage (usually 20+ volts) and cook
> anything attached.  A fast and effective crowbar, if designed correctly,
> will clamp this voltage before it destroys your expensive equipment. With
> switchers my experience has been that one or more of the switching FETs or
> high speed diodes fail and the supply just dies (no output).  Which one
> would you rather have connected to your brand new K3 if it failed?
>
> 73
> Rodger
> N4NRW
> counting down the day till the K3 arrival!
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[Jan Erik Holm]

Mike Penkas wrote:
> I  have 2 SEC1223's and no hash. I also have an Astron RS35 and RS50
> linear supplies.  Sometimes the magnetic hum from them drives me crazy.  
> The little cork pads Astron puts in them to alleviate this
> does not help much. I keep them under the closed console on the floor.
>                      Mike  WA8EBM

Sorry to disagree but the SEC1223 is far from quiet. However it can
be made much better by modifications. The DC side needs much better
filtering, also some work can be done on the AC side.

73 Jim SM2EKM


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[Stewart Baker]

I believe that all new SEC1223's have the mods fitted.

73
Stewart G3RXQ
On Tue, 08 Jul 2008 14:40:27 +0200, Jan Erik Holm wrote:
> Mike Penkas wrote:
>> I  have 2 SEC1223's and no hash. I also have an Astron RS35 and
RS50
>> linear supplies.  Sometimes the magnetic hum from them drives
me crazy.
>> The little cork pads Astron puts in them to alleviate this
>> does not help much. I keep them under the closed console on the
floor.
>> Mike  WA8EBM
>>
> Sorry to disagree but the SEC1223 is far from quiet. However it
can
> be made much better by modifications. The DC side needs much
better

> filtering, also some work can be done on the AC side.
>
> 73 Jim SM2EKM
>
>
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[Bill Coleman-2]

On Jul 8, 2008, at 8:40 AM, Jan Erik Holm wrote:

> Mike Penkas wrote:
>> I  have 2 SEC1223's and no hash. I also have an Astron RS35 and  
>> RS50 linear supplies.  Sometimes the magnetic hum from them drives  
>> me crazy.  The little cork pads Astron puts in them to alleviate this
>> does not help much. I keep them under the closed console on the  
>> floor.
>>                     Mike  WA8EBM
>
> Sorry to disagree but the SEC1223 is far from quiet. However it can
> be made much better by modifications. The DC side needs much better  
> filtering, also some work can be done on the AC side.

I bought a used SEC-1223 at a hamfest to power my K2. I found it  
reasonably quiet on all bands except 160m. I added ferrite beads and  
bypassing to the DC output, and more ferrite to the AC leads and all  
but knocked the birdies completely out of the picture on 160m.

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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