Re: K3/100 and KPA3 Rev C Tech Alert - Important

Eric Swartz - WA6HHQ, Elecraft

Hi Mike,

No, if its clean, you are probably OK. Make sure you are checking at
above 13W so the KPA3 is in-line.

Not ALL KPA3s in the s/n or date range have C3 installed. I actually
listed a slightly widers/n range than we thought the problem occurred in
just to make sure we caught them all. s/n 3008 is at the leading edge
and probably missed it.

As per the app note, you can look through the front top cover vents at
the KPA3 PCB to see if you have a Rev C PCB. Odds are you have the
prior rev.

73, Eric

--- In Elecraft_K3@..., "Leigh" <bipi@...> wrote:


I have serial # 3008. I've checked my signal on a spectrum analyzer
and it is clean. Do all KPA3's with the C3 installed on the board have
this problem or is it possible to show up at a later date?


73 de Mike

----- Original Message -----
From: wa6hhq
To: Elecraft_K3@...
Sent: Tuesday, November 17, 2009 4:05 PM
Subject: [Elecraft_K3] K3/100 and KPA3 Rev C Tech Alert - Important

Spurious TX sidebands due to C3 installation on early Rev C KPA3 PC

We have determined that a small number of K3/100s and KPA3s left the
factory earlier this year with capacitor C3 installed by mistake on
early Revision C KPA3 PC boards. This part location should be empty on
Rev. C KPA3s. Installation of C3 causes the PA bias supply to oscillate
on some KPA3s at approximately 15-20 kHz, resulting in spurious TX
sidebands at that spacing from the carrier.

S/N & Date Range: A small number of K3/100s within approximately S/N
3000-3138. These radios were shipped approximately April 30 to June 2,
2009. Upgrade or repair KPA3s sent separately during this time period
may also be affected.

After June 2, 2009, this problem was corrected for all K3/100s s/n
3139 and later, and all Rev C KPA3s bought as an upgrade. This alert
does not apply to Rev C KPA3s shipped after June 2, 2009.

Symptom: A strong TX spur, approximately -20 dB down from peak
transmit power, spaced approximately 15-20 kHz on each side of the
operating frequency.

Corrective Action: Remove capacitor C3 from the Rev C KPA3 PCB as
described in our detailed Tech note.

A detailed Tech. Alert App note (.pdf) can be downloaded from:

It contains detailed info and pictures.

Its also linked to from our K3 Mods and App notes Page:

We apologize for this issue. We thought we had contacted all of the
K3 owners affected, but we have found a few we missed, so we are posting
this here.

If after reading the Tech. Alert you have questions, please feel
free to contact our Tech. group at k3support@... or via phone at

73, Eric WA6HHQ

Join to automatically receive all group messages.