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KPA500 cabinet buzz

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Michael Blake

KPA500 cabinet buzz

I just built my KPA500 today and on the air reports were good. 20watts Drive seemed right for about 500 watt peaks. After running it for about an hour I shut down to clean up the kit building mess and when I returned later I was hearing a loud 60 cycle mechanical buzz from the left side of the cabinet when in operation. The buzz would vary from very light when keyed with no drive to quite loud when putting out 500 watts CW. I had not noticed any noise earlier but I was wearing Bose noise cancelling headphones as I normally do.

The voltage looks normal under load and the output power is 500 watts with a little over 20 watts drive.

I removed the top cover, loosened the transformer mounting bolt a bit, turned it up on its left side to make sure the transformer was resting against the two bumpers and retightened the mounting screw per the instructions. This did not result in any change in the mechanical vibration.

Any suggestions?

Michael Blake
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Dave AD6A

Re: KPA500 cabinet buzz

My KPA500 (that I built about a year ago) buzzes in the same way as
Michael's.
My transformer is hard against the rubber buffers, the double-rubber pads
are properly in place, and the bolt is nicely torqued down. I'd be
interested in hearing any ideas to mitigate this issue also.

73, Dave AD6A

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Michael Blake
Sent: Thursday, January 25, 2018 5:50 PM
To: Elecraft Mailing List <[hidden email]>
Subject: [Elecraft] KPA500 cabinet buzz

I just built my KPA500 today and on the air reports were good. 20watts Drive
seemed right for about 500 watt peaks. After running it for about an hour I
shut down to clean up the kit building mess and when I returned later I was
hearing a loud 60 cycle mechanical buzz from the left side of the cabinet
when in operation. The buzz would vary from very light when keyed with no
drive to quite loud when putting out 500 watts CW. I had not noticed any
noise earlier but I was wearing Bose noise cancelling headphones as I
normally do.

The voltage looks normal under load and the output power is 500 watts with a
little over 20 watts drive.

I removed the top cover, loosened the transformer mounting bolt a bit,
turned it up on its left side to make sure the transformer was resting
against the two bumpers and retightened the mounting screw per the
instructions. This did not result in any change in the mechanical
vibration.

Any suggestions?

Michael Blake
[hidden email]

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Elecraft mailing list

Re: KPA500 cabinet buzz

My KPA500 hums in standby when PWM controlled heating elements on other circuits are operating. (coffee maker and flat iron, neither of which are mine) I assume it is a power quality problem, but I have no way to be certain.

--ae0mm

-------- Original Message --------
On January 25, 2018 8:46 PM, Dave AD6A <[hidden email]> wrote:

> My KPA500 (that I built about a year ago) buzzes in the same way as
> Michael's.
> My transformer is hard against the rubber buffers, the double-rubber pads
> are properly in place, and the bolt is nicely torqued down. I'd be
> interested in hearing any ideas to mitigate this issue also.
>
> 73, Dave AD6A
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Michael Blake
> Sent: Thursday, January 25, 2018 5:50 PM
> To: Elecraft Mailing List [hidden email]
> Subject: [Elecraft] KPA500 cabinet buzz
>
> I just built my KPA500 today and on the air reports were good. 20watts Drive
> seemed right for about 500 watt peaks. After running it for about an hour I
> shut down to clean up the kit building mess and when I returned later I was
> hearing a loud 60 cycle mechanical buzz from the left side of the cabinet
> when in operation. The buzz would vary from very light when keyed with no
> drive to quite loud when putting out 500 watts CW. I had not noticed any
> noise earlier but I was wearing Bose noise cancelling headphones as I
> normally do.
>
> The voltage looks normal under load and the output power is 500 watts with a
> little over 20 watts drive.
>
> I removed the top cover, loosened the transformer mounting bolt a bit,
> turned it up on its left side to make sure the transformer was resting
> against the two bumpers and retightened the mounting screw per the
> instructions. This did not result in any change in the mechanical
> vibration.
>
> Any suggestions?
>
> Michael Blake
> [hidden email]
>
> ---------------------------------------------------------------
>
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> delivered to [hidden email]
>
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> ---------------------------------------------------------------
>
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Chris Hallinan

Re: KPA500 cabinet buzz

In reply to this post by Dave AD6A

Mine is about 2 months old and has buzzed during key-down since I first
powered it up. Just figured it was that giant toroidal transforming doing
its thing.

Chris K1AY

On Thu, Jan 25, 2018 at 9:46 PM, Dave AD6A <[hidden email]> wrote:

> My KPA500 (that I built about a year ago) buzzes in the same way as
> Michael's.
> My transformer is hard against the rubber buffers, the double-rubber pads
> are properly in place, and the bolt is nicely torqued down. I'd be
> interested in hearing any ideas to mitigate this issue also.
>
> 73, Dave AD6A
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Michael Blake
> Sent: Thursday, January 25, 2018 5:50 PM
> To: Elecraft Mailing List <[hidden email]>
> Subject: [Elecraft] KPA500 cabinet buzz
>
> I just built my KPA500 today and on the air reports were good. 20watts
> Drive
> seemed right for about 500 watt peaks. After running it for about an hour I
> shut down to clean up the kit building mess and when I returned later I was
> hearing a loud 60 cycle mechanical buzz from the left side of the cabinet
> when in operation. The buzz would vary from very light when keyed with no
> drive to quite loud when putting out 500 watts CW. I had not noticed any
> noise earlier but I was wearing Bose noise cancelling headphones as I
> normally do.
>
> The voltage looks normal under load and the output power is 500 watts with
> a
> little over 20 watts drive.
>
> I removed the top cover, loosened the transformer mounting bolt a bit,
> turned it up on its left side to make sure the transformer was resting
> against the two bumpers and retightened the mounting screw per the
> instructions. This did not result in any change in the mechanical
> vibration.
>
> Any suggestions?
>
> Michael Blake
> [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> 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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>
> ______________________________________________________________
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--
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k2qo

Re: KPA500 cabinet buzz

After much searching, this 2.4 year old thread is the only info I can find on
this issue. I bought a factory built KPA500 a few months ago and mine buzzes
on CW key down. Af first I thought maybe this is normal as I never owned an
HF amp. Now I think it is a problem.

Any know how to fix this? I can shoot a short movie if that helps.

73,
Mark K2QO

--
Sent from: http://elecraft.365791.n2.nabble.com/
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Richard P McCoy

Re: KPA500 cabinet buzz

In reply to this post by Michael Blake

Mark:

I have this same issue with my KPA500,
connected to my K3S via AuxIO cable.

It's been that way since new from Elecraft.
It sounds like the AC transformer vibrating against the cabinet?
It's the same on different bands and power levels.

I've just never had the time to research the problem.

73, Dick, N4UN

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

After much searching, this 2.4 year old thread is the only info I can find on
this issue. I bought a factory built KPA500 a few months ago and mine buzzes
on CW key down. Af first I thought maybe this is normal as I never owned an
HF amp. Now I think it is a problem.

Any know how to fix this? I can shoot a short movie if that helps.

73,
Mark K2QO
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Eric Norris-2

Re: KPA500 cabinet buzz

In reply to this post by k2qo

There is KPA500 buzz (normal), and KPA500 BUZZ (abnormal). I own two.

KPA Numero Uno was bought way back when, when the kits were first
available. When I first built it, it buzzed something akin to to your
teeth clacking when you notice a full-grown T. Rex is standing next to
you. At that time, many were complaining about KPA500 buzz, but one must
understand that some would complain that their K3 did not come with the
case stuffed with Krugerands. A call to Support convinced them it was
really loud. They sent me an updated bolt, washer, and spacer set. I very
carefully repositioned the transformer, and torqued the bolt to factory
spec. Several times. No buzz then, no buzz now that I can hear. I do now
have an LP-100A sitting on the top left forward of the cabinet. A perfect
fit. Perhaps that is a dampner, who knows.

KPA500 Numero Two-o was bought this year, is factory-built, and has a very
slight audible buzz on cw. These amps have compact, toroidal, linear
transformers that produce a little buzz. If it ever rises to an annoying
level, I would: 1) Turn off the amp using the front-panel switch to drain
the filter caps and let the fan run all the way down. 2) Turn off the
rear-panel switch. 3) Unlug the amp from A/C. 4. Remove the top cover as
shown in the manual. 5) Using a very strong light, see if the transformer
is touching the cabinet. 6) If so, you can SLIGHTLY. loosen the bolt
(PAY ATTENTION TO THE TIGHTNESS OF THE BOLT IF YOU DO NOT HAVE A TORQUE
WRENCH), and very, very carefully adjust the transformer so it is a hair
away from the cabinet on all sides. 7) Reverse the steps. Repeat if
necessary. OR Call Support. OR wear headphones. OR Fuggedaboutit.
NOTE: You can indeed make it worse. The reason you are probably hearing
it for the first time is that all amps I have owned with linear supplies
also buzz, but the constant fan masks it.

73 Eric WD6DBM

On Sat, May 29, 2021, 5:57 PM k2qo <[hidden email]> wrote:

> After much searching, this 2.4 year old thread is the only info I can find
> on
> this issue. I bought a factory built KPA500 a few months ago and mine
> buzzes
> on CW key down. Af first I thought maybe this is normal as I never owned an
> HF amp. Now I think it is a problem.
>
> Any know how to fix this? I can shoot a short movie if that helps.
>
> 73,
> Mark K2QO
>
>
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
> ______________________________________________________________
> 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]
>

Mike Maloney

Re: KPA500 cabinet buzz

The KPA-500 transformer should be more than just a "hair" away from sides (step 6 above) as there are rubber bumpers and a ribbon cable between that should NOT be pinched. Refer to Kit Assembly Instructions page 35 and figure 52.
Mike AC5P
On Sunday, May 30, 2021, 07:29:59 AM CDT, Eric Norris <[hidden email]> wrote:

There is KPA500 buzz (normal), and KPA500 BUZZ (abnormal). I own two.

KPA Numero Uno was bought way back when, when the kits were first
available. When I first built it, it buzzed something akin to to your
teeth clacking when you notice a full-grown T. Rex is standing next to
you. At that time, many were complaining about KPA500 buzz, but one must
understand that some would complain that their K3 did not come with the
case stuffed with Krugerands. A call to Support convinced them it was
really loud. They sent me an updated bolt, washer, and spacer set. I very
carefully repositioned the transformer, and torqued the bolt to factory
spec. Several times. No buzz then, no buzz now that I can hear. I do now
have an LP-100A sitting on the top left forward of the cabinet. A perfect
fit. Perhaps that is a dampner, who knows.

KPA500 Numero Two-o was bought this year, is factory-built, and has a very
slight audible buzz on cw. These amps have compact, toroidal, linear
transformers that produce a little buzz. If it ever rises to an annoying
level, I would: 1) Turn off the amp using the front-panel switch to drain
the filter caps and let the fan run all the way down. 2) Turn off the
rear-panel switch. 3) Unlug the amp from A/C. 4. Remove the top cover as
shown in the manual. 5) Using a very strong light, see if the transformer
is touching the cabinet. 6) If so, you can SLIGHTLY. loosen the bolt
(PAY ATTENTION TO THE TIGHTNESS OF THE BOLT IF YOU DO NOT HAVE A TORQUE
WRENCH), and very, very carefully adjust the transformer so it is a hair
away from the cabinet on all sides. 7) Reverse the steps. Repeat if
necessary. OR Call Support. OR wear headphones. OR Fuggedaboutit.
NOTE: You can indeed make it worse. The reason you are probably hearing
it for the first time is that all amps I have owned with linear supplies
also buzz, but the constant fan masks it.

73 Eric WD6DBM

On Sat, May 29, 2021, 5:57 PM k2qo <[hidden email]> wrote:

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Richard P McCoy

KPA500 cabinet buzz

In reply to this post by Richard P McCoy

---------- Forwarded message ---------
From: Mike Flowers <[hidden email]>
Date: Sat, May 29, 2021 at 11:11 PM
Subject: Re: [Elecraft] KPA500 cabinet buzz

Hi Mark,

I’d verify this with Elecraft Support.

When I got my KPA500 it was used and shipped with the transformer in a
separate box.

The assembly manual was very specific about how to position and tighten the
washer and wing nut holding the transformer in place. Important to avoid
mechanical buzzing …

Perhaps downloading the KPA500 Assembly manual could provide some guidance.

-- 73 de Mike Flowers, K6MKF, NCDXC - "It's about DX!"

> On May 29, 2021, at 8:39 PM, Richard P McCoy <[hidden email]> wrote:
>
> Mark:
>
> I have this same issue with my KPA500,
> connected to my K3S via AuxIO cable.
>
> It's been that way since new from Elecraft.
> It sounds like the AC transformer vibrating against the cabinet?
> It's the same on different bands and power levels.
>
> I've just never had the time to research the problem.
>
> 73, Dick, N4UN
>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>
> After much searching, this 2.4 year old thread is the only info I can

find on
> this issue. I bought a factory built KPA500 a few months ago and mine
buzzes
> on CW key down. Af first I thought maybe this is normal as I never owned
an

> HF amp. Now I think it is a problem.
>
> Any know how to fix this? I can shoot a short movie if that helps.
>
> 73,
> Mark K2QO
> ______________________________________________________________
> 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]

ANDY DURBIN

KPA500 cabinet buzz

In reply to this post by Michael Blake

"The KPA-500 transformer should be more than just a "hair" away from sides (step 6 above) as there are rubber bumpers and a ribbon cable between that should NOT be pinched. "

Over the production life of the KPA500 the transformer design, and perhaps the supplier, have changed several times. The transformer supplied with my kit was significantly larger in diameter that the one shown in the assembly manual photos. The only way I could ensure clearance was to shim the transformer before tightening the bolt and remove the shims afterwards. There is very little clearance, perhaps 2 cereal box thicknesses, but I didn't record the shim stack.

Andy, k3wyc
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Eric Norris-2

Re: KPA500 cabinet buzz

In reply to this post by Mike Maloney

I didn't say " a hair's width," I said "a hair," a technical term
understood by OFs as an approximation. I also didn't say "pinch the ribbon
cable," because that is not the side of the cabinet where the problem lies
in my experience.

Now, are you guys telling me there is an actual wing-nut on the KPA500
transformer hold-down bolt on modern units? If so, forget the torque
wrench and try tightening the wing-nut a hair--after following all safety
precautions outlined in the manual or my OP.

By all means refer to the original KPA500 Assembly Manual.

Good luck, pilgrim.

73 Eric WD6DBM

A Mr Richard Fedder of Fort Wayne, N.J. wrote:

> The KPA-500 transformer should be more than just a "hair" away from sides
> (step 6 above) as there are rubber bumpers and a ribbon cable between that
> should NOT be pinched. Refer to Kit Assembly Instructions page 35 and
> figure 52...
>
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k2qo

Re: KPA500 cabinet buzz

In reply to this post by Michael Blake