[Elecraft] K3 Amplifier Drive Inconsistency

[Jim Rhodes]

Last night I noticed I had little to no output from my KX3/KXPA100 combo
especially on 40. I did a little experimenting and discovered that 3 turns
of the transmit audio line through an unknown mix clamp on ferrite fixed
the problem. Without it I was mildly affected on 20 and not at all on 15.
With that choke in place I was stable on 40 and all other bands I tried. I
am currently portable for work (in North Dakota) and am using a mobile
antenna clamped to the top of a 6 ft tall wooden fence. Without the choke
the ALC would go up when keyed, then drop off to near nothing. I know AFSK
is becoming a more preferred method of generating RTTY, but I have never
had this issue with FSK. So I learned a lesson about the little USB
soundcard I use for portable ops.

On Mon, Aug 5, 2019 at 6:34 PM <donovanf at starpower.net> wrote:

> Hi Bill,
>
>
> I've never experienced your reported amplifier drive problem with
> my K3 s/n #6100 driving 20 watts into my Lunar Link LA-62
> 1500 watt output 6 meter amplifier. Perhaps it unique to the
> K3 - KPA1500 combination.
>
>
> 73
> Frank
> W3LPL
>
> ----- Original Message -----
>
> From: "Bill Schwantes" <bill4070 at gmail.com>
> To: elecraft at mailman.qth.net
> Sent: Monday, August 5, 2019 11:24:54 PM
> Subject: [Elecraft] K3 Amplifier Drive Inconsistency
>
> I need help solving an amplifier drive inconsistency problem when I
> operate
> using digital modes on 50 MHz. I noticed during a recent contest that the
> K3 will sometimes key the amplifier but provide zero drive. I'm using K3
> SN
> 669 on 50 MHz FT8, FT4 and MSK 144 and driving a KPA1500 to about 750
> watts.
>
> After several consecutive transmissions I notice that the amplifier
> responds briefly to being keyed but the power drops to zero. It's keyed up
> but has no output. The K3's output (drive) is set at 17 watts but there is
> no output on the RF meter when this happens. The K3's red TX indicator is
> on. This problem also occurs when driving a KPA500, though less often
>
> I can correct this problem temporarily by switching the amplifier to
> standby, which allows the K3 to change to "barefoot" output then switch
> the amplifier back to "operate" which changes drive power back to it's
> preset level. That's usually good for a dozen or so transmit cycles before
> the problem reappears.
>
> This problem does not occur when driving other amplifiers; nor does it
> occur when using CW or SSB modes. It seems to have something to do with
> the
> K3/KPA1500 command interface controlling the output power of the K3.
>
> Any ideas?
>
> 73 Bill W7QQ
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