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KPA500 code oscillator

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W1GO (Joe)

KPA500 code oscillator

Hi all,

Finished assembly of KPA500 and a little surprised at the magnitude of hum / buzz during CW (no real issue on SSB); I've read about it but was surprised at just how pronounced it is. I could use the KPA500 as a code oscillator for practice; no need to keep monitor turned on. I've read most of the historical dialogue regarding methods to minimize "the buzz": use yellow wire tap, keep wires from touching chassis, make sure everything (including transformer) is good and tight, etc. all those things are done with little positive impact. I'm running off well regulated 240 VAC.

I just wonder if anyone has any other "secrets" they might share. My code proficiency is not great, at this point, and having the KPA500 groan in response to my keying is somewhat distracting; even with headphones when monitor is turned up higher than usual.

Best regards,

Joe
W1GO
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joeduerbusch

Re: KPA500 code oscillator

Hl Joe, I also have a KPA500. It also had the Buzz and noise. I sent it
in to Elecraft for a different reason, and they found a Bad "Z-Bracket" and
replaced it. Now is the KPA500 is silent except for the loud fan.
Mine was factory built, so I don't know what this bracket is, but think you
should take a look at it.

Joe K0BX

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On Sun, Oct 23, 2016 at 5:46 PM, W1GO (Joe) <[hidden email]> wrote:

>
> Hi all,
>
> Finished assembly of KPA500 and a little surprised at the magnitude of hum
> / buzz during CW (no real issue on SSB); I've read about it but was
> surprised at just how pronounced it is. I could use the KPA500 as a code
> oscillator for practice; no need to keep monitor turned on. I've read most
> of the historical dialogue regarding methods to minimize "the buzz": use
> yellow wire tap, keep wires from touching chassis, make sure everything
> (including transformer) is good and tight, etc. all those things are done
> with little positive impact. I'm running off well regulated 240 VAC.
>
> I just wonder if anyone has any other "secrets" they might share. My code
> proficiency is not great, at this point, and having the KPA500 groan in
> response to my keying is somewhat distracting; even with headphones when
> monitor is turned up higher than usual.
>
> Best regards,
>
> Joe
> W1GO
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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W1GO (Joe)

Re: KPA500 code oscillator

Thanks, Ron. Did all suggested and ensured every screw and bolt tightened. Reseated transformer and really tightened down. Unfortunately, same hum on CW; even with less than 10W drive.

Back to the drawing board.

Thank you,

Joe
W1GO

> On Oct 23, 2016, at 5:56 PM, Ron D'Eau Claire <[hidden email]> wrote:
>
> When you remove the KPA500 top cover, the Z-bracket is the metal bracket
> running from the front to back panels dividing the inside into the power
> supply (with the big transformer) and RF sections.
>
> The Z-bracket attaches to the front and back panels, the bottom cover and to
> the top. Make sure you got all the screws tight.
>
> Also, be sure you installed the transformer correctly, including the rubber
> disk between the transformer and the bottom cover and you have the bumpers
> in place where the transformer rests against edge. Be sure the Bellevue
> washer is installed right side up. That's the washer under the nut holding
> the transformer in place. As the text explained, it is very slightly conical
> and must be installed so the center hole of the washer is slightly higher
> than the edges. Put it on the desk and tap on the edges of the washer with a
> pencil. If it rocks a bit, it is upside. If it is right side up, it will sit
> still. Be sure it is installed right side up.
>
> Finally, tighten the nut on the Bellevue washer a bit more. If you have a
> torque wrench available, it should be set to 55 in/lbs but it is not real
> critical. As the text says, run the washer down onto the Bellevue washer,
> and then tighten one or two turns further. IF needed add a bit more to quiet
> it!
>
> My KPA500 hums under full load, but not loudly - about as loud as my Astron
> power supply under full load. If anything is "buzzing" it is certainly a
> loose fastener somewhere.
>
> 73, Ron AC7AC
>

W1GO (Joe)

Re: KPA500 code oscillator

In reply to this post by W1GO (Joe)

Al,

Quick follow-up on the KPA500 with the very loud buzzing transformer … after hours of disassembling, reassembling, tightening, etc., I couldn’t correct the problem and sent the unit back to the mother ship. The transformer had a problem and was replaced. I have heard from others that they were similarly told of a problem with transformers that would require replacement. My unit is now wonderfully quiet.

My unit was a kit, but it makes me wonder if the “burn-in” of assembled units is simply an idle current test or if the unit it tested under load at different modes; my unit was quiet on SSB but ferociously loud on CW (even at 5W drive). It seems that would be pretty easy to detect in an assembled unit; kits are a whole other story.

In any event, aside for the $80+ it cost me to ship the unit back, all is well … and quiet.

Joe W1GO

> On Oct 23, 2016, at 5:46 PM, W1GO (Joe) <[hidden email]> wrote:
>
>
> Hi all,
>
> Finished assembly of KPA500 and a little surprised at the magnitude of hum / buzz during CW (no real issue on SSB); I've read about it but was surprised at just how pronounced it is. I could use the KPA500 as a code oscillator for practice; no need to keep monitor turned on. I've read most of the historical dialogue regarding methods to minimize "the buzz": use yellow wire tap, keep wires from touching chassis, make sure everything (including transformer) is good and tight, etc. all those things are done with little positive impact. I'm running off well regulated 240 VAC.
>
> I just wonder if anyone has any other "secrets" they might share. My code proficiency is not great, at this point, and having the KPA500 groan in response to my keying is somewhat distracting; even with headphones when monitor is turned up higher than usual.
>
> Best regards,
>
> Joe
> W1GO
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]