Elecraft

KPA500 Transformer

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Jim Spikes N4KH

KPA500 Transformer

Looking for details from anyone who resolved issues with excessive
transformer hum during transmit on a KPA-500.

I have a hum mitigation application note sent from Elecraft tech support.
But the procedure recommended is pretty involved - removing front/side
panels, un-plugging connections, removing the transformer, changing
positions of the rubber discs, and putting it back together. Possibly more
than once, depending on the results.

There is a risk of breaking something, and I'm not sure its going to solve
the problem if I'm successful. This is a new out of the box KPA500 kit.

If anybody has any lessons learned I would appreciate hearing them.

Jim, N4KH

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Alan - G4GNX

Re: KPA500 Transformer

I don't see the problem. I presume you bought a kit to assemble it
yourself. You simply reverse part of the assembly procedure, then
re-assemble it. I've assembled several KPA500s and I'd bet that you
didn't quite get it right first time. There's no shame in that. This is
a risk you take with self-assembly. ISTR there's a torque wrench setting
for tightening. Did you use one?

Have confidence. Take it apart, do as they say and enjoy feeling smug
that you fixed it yourself. :-)

Lessons learned? Yeah, take your time, follow instructions to the
letter. Don't do anything if you're tired. Plenty of space. Plenty of
light. The right tools and a suitable container for parts.

73,

Alan. G4GNX

------ Original Message ------
From: "Jim Spikes N4KH" <[hidden email]>
To: [hidden email]
Sent: 20/10/2020 00:59:06
Subject: [Elecraft] KPA500 Transformer

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Eric Norris-2

Re: KPA500 Transformer

In reply to this post by Jim Spikes N4KH

Hi Jim,

I had a bad hum from my KPA500 kit, an early model. Elecraft sent me a new
center bolt that was only threaded on the end--the original bolt had
threads all along the shaft. Also an additional pad.

Assuming you assembled it all correctly, try these two things: If you have
a torque wrench, tighten the bolt to the exact spec. If you don't have
one, try slightly tightening or even loosening the bolt. Second, make sure
the transformer is exactly centered on the bolt and not touching any of the
sheet metal, including the side panel. Use a strong flashlight to check it
with the top removed. UNPLUG THE AMP FIRST!

Mine has been hum-free for years, after the tweaking.

73 Eric WD6DBM

On Mon, Oct 19, 2020, 5:00 PM Jim Spikes N4KH <[hidden email]> wrote:

> Looking for details from anyone who resolved issues with excessive
> transformer hum during transmit on a KPA-500.
>
>
>
> I have a hum mitigation application note sent from Elecraft tech support.
> But the procedure recommended is pretty involved - removing front/side
> panels, un-plugging connections, removing the transformer, changing
> positions of the rubber discs, and putting it back together. Possibly more
> than once, depending on the results.
>
>
>
> There is a risk of breaking something, and I'm not sure its going to solve
> the problem if I'm successful. This is a new out of the box KPA500 kit.
>
>
>
> If anybody has any lessons learned I would appreciate hearing them.
>
>
>
> Jim, N4KH
>
> ______________________________________________________________
> 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]
>

Eric Norris-2

Re: KPA500 Transformer

In reply to this post by Jim Spikes N4KH

When the KPA500 first came out, there were lots of complaints about hum.
This made it difficult for Elecraft Support to differentiate between normal
hum, which I can barely hear, to the obnoxiously loud hum of a misaligned
transformer. I finally called support so they could hear the hum of my
KPA500, which was in the obnoxious category.

Take a breath, you can fix this. Tweaking the bolt torque, and slightly
moving the transformer, requires only removing the cover. If you don't own
and can't borrow a torque wrench, given your investment--buy one. A small,
inexpensive one will do the trick as the torque is quite low.

73 Eric WD6DBM

On Mon, Oct 19, 2020, 5:00 PM Jim Spikes N4KH <[hidden email]> wrote:

Macy monkeys

Re: KPA500 Transformer

Even the 'normal' hum was too much my tastes. My KPA500 is now on the floor, under the desk with a remote digital readout on the desk.

John K7FD

> On Oct 19, 2020, at 6:25 PM, Eric Norris <[hidden email]> wrote:
>
> When the KPA500 first came out, there were lots of complaints about hum.
> This made it difficult for Elecraft Support to differentiate between normal
> hum, which I can barely hear, to the obnoxiously loud hum of a misaligned
> transformer. I finally called support so they could hear the hum of my
> KPA500, which was in the obnoxious category.
>
> Take a breath, you can fix this. Tweaking the bolt torque, and slightly
> moving the transformer, requires only removing the cover. If you don't own
> and can't borrow a torque wrench, given your investment--buy one. A small,
> inexpensive one will do the trick as the torque is quite low.
>
> 73 Eric WD6DBM
>
>> On Mon, Oct 19, 2020, 5:00 PM Jim Spikes N4KH <[hidden email]> wrote:
>>
>> Looking for details from anyone who resolved issues with excessive
>> transformer hum during transmit on a KPA-500.
>>
>>
>>
>> I have a hum mitigation application note sent from Elecraft tech support.
>> But the procedure recommended is pretty involved - removing front/side
>> panels, un-plugging connections, removing the transformer, changing
>> positions of the rubber discs, and putting it back together. Possibly more
>> than once, depending on the results.
>>
>>
>>
>> There is a risk of breaking something, and I'm not sure its going to solve
>> the problem if I'm successful. This is a new out of the box KPA500 kit.
>>
>>
>>
>> If anybody has any lessons learned I would appreciate hearing them.
>>
>>
>>
>> Jim, N4KH
>>
>> ______________________________________________________________
>> 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]
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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VE3NR

Re: KPA500 Transformer

In reply to this post by Jim Spikes N4KH

Toroidal transformers cause very little acoustic hum, unless the core
is not tightly wound or the copper wire windings are loose!

If you have to tighten the mounting bolt with a torque wrench
to get the transformer quiet, something is wrong!

Bert VE3NR

On 2020-10-19 19:59, Jim Spikes N4KH wrote:

Eric Norris-2

Re: KPA500 Transformer

The torque spec is called out in the manual. Why not use a torque wrench?
Can we please not resurrect the KPA500 hum thread already beat to death
multiple times years ago? Or does everyone need to chime in yet again?

55 inch-pounds.

73 Eric WD6DBM

On Mon, Oct 19, 2020, 9:15 PM Bert <[hidden email]> wrote:

> Toroidal transformers cause very little acoustic hum, unless the core
> is not tightly wound or the copper wire windings are loose!
>
> If you have to tighten the mounting bolt with a torque wrench
> to get the transformer quiet, something is wrong!
>
> Bert VE3NR
>
>
>
>
> On 2020-10-19 19:59, Jim Spikes N4KH wrote:
> > Looking for details from anyone who resolved issues with excessive
> > transformer hum during transmit on a KPA-500.
> >
> >
> >
> > I have a hum mitigation application note sent from Elecraft tech support.
> > But the procedure recommended is pretty involved - removing front/side
> > panels, un-plugging connections, removing the transformer, changing
> > positions of the rubber discs, and putting it back together. Possibly
> more
> > than once, depending on the results.
> >
> >
> >
> > There is a risk of breaking something, and I'm not sure its going to
> solve
> > the problem if I'm successful. This is a new out of the box KPA500 kit.
> >
> >
> >
> > If anybody has any lessons learned I would appreciate hearing them.
> >
> >
> >
> > Jim, N4KH
> >
> > ______________________________________________________________
> > 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]
>
> ______________________________________________________________
> 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
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>

Alan - G4GNX

Re: KPA500 Transformer

In reply to this post by VE3NR

Then perhaps someone needs to educate Elecraft not to specify use of a
torque wrench, in their assembly instructions. ;-)

73,

Alan. G4GNX

------ Original Message ------
From: "Bert" <[hidden email]>
To: [hidden email]
Sent: 20/10/2020 05:15:21
Subject: Re: [Elecraft] KPA500 Transformer

>Toroidal transformers cause very little acoustic hum, unless the core
>is not tightly wound or the copper wire windings are loose!
>
>If you have to tighten the mounting bolt with a torque wrench
>to get the transformer quiet, something is wrong!
>
>Bert VE3NR
>

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David Christ

Re: KPA500 Transformer

Torque wrenches are used for two reasons:

1) to make sure things are tight enough

2) to make sure things are not tightened too much.

Stating the proper torque is good engineering practice. For common screws and bolts one can find the suggested torque in reference books and online. For special circumstances the manufacturer should publish the proper values.

David K0LUM

> On Oct 20, 2020, at 5:31 AM, Alan - G4GNX <[hidden email]> wrote:
>
> Then perhaps someone needs to educate Elecraft not to specify use of a torque wrench, in their assembly instructions. ;-)
>
> 73,
>
> Alan. G4GNX
>
>
> ------ Original Message ------
> From: "Bert" <[hidden email]>
> To: [hidden email]
> Sent: 20/10/2020 05:15:21
> Subject: Re: [Elecraft] KPA500 Transformer
>
>> Toroidal transformers cause very little acoustic hum, unless the core
>> is not tightly wound or the copper wire windings are loose!
>>
>> If you have to tighten the mounting bolt with a torque wrench
>> to get the transformer quiet, something is wrong!
>>
>> Bert VE3NR
>>
>
> ______________________________________________________________
> 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
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VE3NR

Re: KPA500 Transformer

In reply to this post by Jim Spikes N4KH

Agree 100%!!!
Bert VE3NR

On 2020-10-20 8:11, jimn4kh wrote:

> I wasn't my intention to resurrect an old thread. I checked the
> archives before posting my message yesterday. I found a little info
> but not much. Perhaps I missed it. I delayed going to the list but
> Elecraft tech support is apparently really backed up because I've
> gotten zero response to my emails and voicemails beyond one email with
> the hum mitigation tech note I mentioned before. I thought perhaps the
> larger community had a specific solution. Judging from the widely
> varied responses I've gotten ovciously not. I've tightened, loosened,
> and moved the transformer around multiple times with no change. I'll
> go get a torque wrench and try that but I cant imagine it resolving
> the problem given how loud it is. Ill take it all apart first and try
> the procedure once and see if it helps. I just dont like having to
> solve problems through expermention on a $2k+ amplifier.
> Jim N4KH
>
>
> Sent from my Verizon, Samsung Galaxy smartphone
>
>
> -------- Original message --------
> From: Eric Norris <[hidden email]>
> Date: 10/19/20 11:37 PM (GMT-06:00)
> To: Bert <[hidden email]>
> Cc: "elecraft@mailman qth. net" <[hidden email]>
> Subject: Re: [Elecraft] KPA500 Transformer
>
> The torque spec is called out in the manual. Why not use a torque wrench?
> Can we please not resurrect the KPA500 hum thread already beat to death
> multiple times years ago? Or does everyone need to chime in yet again?
>
> 55 inch-pounds.
>
> 73 Eric WD6DBM
>
> On Mon, Oct 19, 2020, 9:15 PM Bert <[hidden email]> wrote:
>
> > Toroidal transformers cause very little acoustic hum, unless the core
> > is not tightly wound or the copper wire windings are loose!
> >
> > If you have to tighten the mounting bolt with a torque wrench
> > to get the transformer quiet, something is wrong!
> >
> > Bert VE3NR
> >
> >
> >
> >
> > On 2020-10-19 19:59, Jim Spikes N4KH wrote:
> > > Looking for details from anyone who resolved issues with excessive
> > > transformer hum during transmit on a KPA-500.
> > >
> > >
> > >
> > > I have a hum mitigation application note sent from Elecraft tech
> support.
> > > But the procedure recommended is pretty involved - removing front/side
> > > panels, un-plugging connections, removing the transformer, changing
> > > positions of the rubber discs, and putting it back together. Possibly
> > more
> > > than once, depending on the results.
> > >
> > >
> > >
> > > There is a risk of breaking something, and I'm not sure its going to
> > solve
> > > the problem if I'm successful. This is a new out of the box KPA500
> kit.
> > >
> > >
> > >
> > > If anybody has any lessons learned I would appreciate hearing them.
> > >
> > >
> > >
> > > Jim, N4KH
> > >
> > > ______________________________________________________________
> > > 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]
> >
> > ______________________________________________________________
> > 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]
> >
> ______________________________________________________________
> 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]

Alan - G4GNX

Re: JIM's KPA 500 transformer [was: KPA500 Transformer]

Jim.

I don't see this as resurrecting an old thread. You've asked for help in
your particular circumstance, not to discuss the merits of a generic
transformer.

As you seem to have done almost everything sensible, if the correct
torque doesn't correct it, I think your only recourse is to get back on
to Elecraft and tell them you think the transformer's faulty.

In the meantime, I guess the only thing you can do is either not use it,
or wear headphones and try to ignore it.

73,

Alan. G4GNX

>
>On 2020-10-20 8:11, jimn4kh wrote:
>>I wasn't my intention to resurrect an old thread. I checked the archives before posting my message yesterday. I found a little info but not much. Perhaps I missed it. I delayed going to the list but Elecraft tech support is apparently really backed up because I've gotten zero response to my emails and voicemails beyond one email with the hum mitigation tech note I mentioned before. I thought perhaps the larger community had a specific solution. Judging from the widely varied responses I've gotten obviously not. I've tightened, loosened, and moved the transformer around multiple times with no change. I'll go get a torque wrench and try that but I cant imagine it resolving the problem given how loud it is. Ill take it all apart first and try the procedure once and see if it helps. I just don't like having to solve problems through experimentation on a $2k+ amplifier.
>>Jim N4KH
>>
>>

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Don Wilhelm

Re: JIM's KPA 500 transformer [was: KPA500 Transformer]

Jim,

If your KPA500 is older, there was a change to the transformer mounting
which added a couple washers to the assembly - both under and above the
transformer. Contact [hidden email] for details and availability
of the kit.

>>
>> On 2020-10-20 8:11, jimn4kh wrote:
>>> I wasn't my intention to resurrect an old thread. I checked the
>>> archives before posting my message yesterday. I found a little info
>>> but not much. Perhaps I missed it. I delayed going to the list but
>>> Elecraft tech support is apparently really backed up because I've
>>> gotten zero response to my emails and voicemails beyond one email
>>> with the hum mitigation tech note I mentioned before. I thought
>>> perhaps the larger community had a specific solution. Judging from
>>> the widely varied responses I've gotten obviously not. I've
>>> tightened, loosened, and moved the transformer around multiple times
>>> with no change. I'll go get a torque wrench and try that but I cant
>>> imagine it resolving the problem given how loud it is. Ill take it
>>> all apart first and try the procedure once and see if it helps. I
>>> just don't like having to solve problems through experimentation on a
>>> $2k+ amplifier.
>>> Jim N4KH

Rich NE1EE

Re: JIM's KPA 500 transformer [was: KPA500 Transformer]

In reply to this post by Alan - G4GNX

Elecraft post acknowledgement - reply to direct post by another

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David Gilbert-2

Re: KPA500 Transformer

In reply to this post by Eric Norris-2

Because everyone who now owns a KPA500 owned it years ago and was a list
member back then??

Besides, I've been a member of this list since at least 2008 and I can
recall many KPA500 owners still complaining about hum even after trying
to follow all of the advice given here. It's still a valid topic and
not outside the list boundary rules.

And of course, every single post in this recent KPA500 hum thread has
been clearly identified in the headline and could be easily ignored or
deleted by anyone who was able to read it. You could have done so
yourself in far less time than it took you to write your post.

Dave AB7E

On 10/19/2020 9:34 PM, Eric Norris wrote:
> The torque spec is called out in the manual. Why not use a torque wrench?
> Can we please not resurrect the KPA500 hum thread already beat to death
> multiple times years ago? Or does everyone need to chime in yet again?
>
> 55 inch-pounds.
>
> 73 Eric WD6DBM

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Nr4c

Re: KPA500 Transformer

In reply to this post by Alan - G4GNX

No, no. The torque wrench is used to insure the proper torque is applied.

A torque wrench is not a torque multiplier, it is a measurement instrument.

Sent from my iPhone
...nr4c. bill

> On Oct 20, 2020, at 6:33 AM, Alan - G4GNX <[hidden email]> wrote:
>
> Then perhaps someone needs to educate Elecraft not to specify use of a torque wrench, in their assembly instructions. ;-)
>
> 73,
>
> Alan. G4GNX
>
>
> ------ Original Message ------
> From: "Bert" <[hidden email]>
> To: [hidden email]
> Sent: 20/10/2020 05:15:21
> Subject: Re: [Elecraft] KPA500 Transformer
>
>> Toroidal transformers cause very little acoustic hum, unless the core
>> is not tightly wound or the copper wire windings are loose!
>>
>> If you have to tighten the mounting bolt with a torque wrench
>> to get the transformer quiet, something is wrong!
>>
>> Bert VE3NR
>>
>
> ______________________________________________________________
> 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]

Elecraft mailing list

Re: KPA500 Transformer

In reply to this post by David Gilbert-2

Here is a video that shows what the root issue may actually be.
https://youtu.be/80XN7OHoBSc

On Tuesday, October 20, 2020, 02:11:51 PM EDT, David Gilbert <[hidden email]> wrote:

Because everyone who now owns a KPA500 owned it years ago and was a list
member back then??

Besides, I've been a member of this list since at least 2008 and I can
recall many KPA500 owners still complaining about hum even after trying
to follow all of the advice given here. It's still a valid topic and
not outside the list boundary rules.

And of course, every single post in this recent KPA500 hum thread has
been clearly identified in the headline and could be easily ignored or
deleted by anyone who was able to read it. You could have done so
yourself in far less time than it took you to write your post.

Dave AB7E

On 10/19/2020 9:34 PM, Eric Norris wrote:
> The torque spec is called out in the manual. Why not use a torque wrench?
> Can we please not resurrect the KPA500 hum thread already beat to death
> multiple times years ago? Or does everyone need to chime in yet again?
>
> 55 inch-pounds.
>
> 73 Eric WD6DBM

______________________________________________________________
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______________________________________________________________
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Josh Fiden

Re: KPA500 Transformer

In reply to this post by Nr4c

Yes. 100% of the time I’ve specified using a calibrated torque wrench or driver in an assembly procedure is to prevent *too much* torque from being applied.

73
Josh W6XU

Sent from my mobile device

> On Oct 20, 2020, at 11:43 AM, Nr4c <[hidden email]> wrote:
>
> No, no. The torque wrench is used to insure the proper torque is applied.
>
> A torque wrench is not a torque multiplier, it is a measurement instrument.
>

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Alan - G4GNX

Re: KPA500 Transformer

In reply to this post by Nr4c

Guys. My comment was sarcastic and has a smiley on the end of it.
Elecraft know what they're doing and I would not expect anyone to tell
them they got it wrong!

73,

Alan. G4GNX

------ Original Message ------
From: "Nr4c" <[hidden email]>
To: "Alan - G4GNX" <[hidden email]>
Cc: "Elecraft Reflector" <[hidden email]>
Sent: 20/10/2020 19:42:31
Subject: Re: [Elecraft] KPA500 Transformer

> No, no. The torque wrench is used to insure the proper torque is applied.
>
>A torque wrench is not a torque multiplier, it is a measurement instrument.
>
>Sent from my iPhone
>...nr4c. bill
>
>
>> On Oct 20, 2020, at 6:33 AM, Alan - G4GNX <[hidden email]> wrote:
>>
>> Then perhaps someone needs to educate Elecraft not to specify use of a torque wrench, in their assembly instructions. ;-)
>>
>> 73,
>>
>> Alan. G4GNX
>>
>>

Elecraft mailing list

Re: KPA500 Transformer

Gee Alan, we get told that all the time, specially by coworkers… <GRIN>

As for the transformer, the tech support guys give good advice here. Place the rubber disks below the transformer in the appropriate places, and one above as the instructions indicate.
Essentially you want to get the transformer off the base chassis enough to keep it from vibrating against it. We all worry about tightening the nut down too much, which is why we added the torque wrench suggestion in the manual. But it does need to be rather tight to keep things from vibrating. Also, make sure all the screws in the chassis are tight. The hum can come from other parts as well. Making sure thins like the rectifier board are properly tight can help alleviate this situation also.

Someone asked about keeping the rear-panel power on. I have the first KPA500 still in operation, and it has seen very little rear-panel off time during its life. In this situation, the power supply is on, and the microcontroller is on in sleep mode. This means the unit does draw current, but not very much. I have seen no effect from it on my power bill. During months when I participate in contests I can’t say that - running 500 or so watts for long periods each weekend does spin the power meter a bit.

Thanks for the compliment, we work very hard to create, build and support products that make you guys happy. I think it shows.

73!
Jack, W6FB
Elecraft Engineering

> On Oct 20, 2020, at 2:27 PM, Alan - G4GNX <[hidden email]> wrote:
>
> Guys. My comment was sarcastic and has a smiley on the end of it. Elecraft know what they're doing and I would not expect anyone to tell them they got it wrong!
>
> 73,
>
> Alan. G4GNX
>
>
> ------ Original Message ------
> From: "Nr4c" <[hidden email]>
> To: "Alan - G4GNX" <[hidden email]>
> Cc: "Elecraft Reflector" <[hidden email]>
> Sent: 20/10/2020 19:42:31
> Subject: Re: [Elecraft] KPA500 Transformer
>
>> No, no. The torque wrench is used to insure the proper torque is applied.
>>
>> A torque wrench is not a torque multiplier, it is a measurement instrument.
>>
>> Sent from my iPhone
>> ...nr4c. bill
>>
>>
>>> On Oct 20, 2020, at 6:33 AM, Alan - G4GNX <[hidden email]> wrote:
>>>
>>> Then perhaps someone needs to educate Elecraft not to specify use of a torque wrench, in their assembly instructions. ;-)
>>>
>>> 73,
>>>
>>> Alan. G4GNX
>>>
>>>
>
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