QRP K2 10m power output

[Ben Hofmann K1NT]

When I first built K2 #4429 in the fall of '04 I was
very careful with the winding/installation of T2
(following the App note on the Elecraft web site) in
order to get full 10w out on 10m.  My recollection is
that I was able to get at least 10w at 28.0 MHz, and
like 9.8w at 28.8 MHz, which I could live with, and
made no further changes.

This week I was performing the power control mod (R98)
and noticed that I was only getting a maximum of 7.5w
at 28.8 MHz.  While performing this mod, I had my
completed, but un-installed KPA100 in line, and I
thought maybe there was a difference in power output
measurement between the base K2 and the K2/100, so I
completely disconnected the KPA100, and replaced R98
with the original resistor to re-measure output on
28.8 MHz, getting again 7.5w or so.

The only changes I've made since my original
build/alignment is the addition of a K6XX/N0SS zero
beat indicator, addition of the K160RX module,
addition of 1 capacitor in VCO area to bring VCO
voltages into correct ranges after the addition of
K160RX, and the addition of the RF/12V connectors for
the KPA100.  I wonder what might have changed to lower
the 10m output?

-Ben  K1NT
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[Ron D'Eau Claire-2]

That is odd, Ben.

Any band-specific power change is usually associated with the bandpass
filters for that band. Ten meters could be an exception because the K2
transmit chain has the lowest gain at that band, so if something is reducing
your overall power output, it might only cause you to fail to meet specs on
that one band. Are you getting the amount of power you've previously had on
the other bands at full power output? If so then it is a 10-meter-only
situation.

If that's the case, I'd look very closely at all the BPF components
associated with 10 meters, including the relay pins, for a missed or poor
solder joint. Sometimes a bad joint doesn't show up for years, depending
upon the environment in which it's used. Then, as oxidation starts to find
its way into the space where the unsoldered lead touches the pad, things
start changing.

Ron AC7AC

-----Original Message-----
When I first built K2 #4429 in the fall of '04 I was
very careful with the winding/installation of T2
(following the App note on the Elecraft web site) in
order to get full 10w out on 10m.  My recollection is
that I was able to get at least 10w at 28.0 MHz, and
like 9.8w at 28.8 MHz, which I could live with, and
made no further changes.

This week I was performing the power control mod (R98)
and noticed that I was only getting a maximum of 7.5w
at 28.8 MHz.  While performing this mod, I had my
completed, but un-installed KPA100 in line, and I
thought maybe there was a difference in power output measurement between the
base K2 and the K2/100, so I completely disconnected the KPA100, and
replaced R98 with the original resistor to re-measure output on 28.8 MHz,
getting again 7.5w or so.

The only changes I've made since my original
build/alignment is the addition of a K6XX/N0SS zero
beat indicator, addition of the K160RX module,
addition of 1 capacitor in VCO area to bring VCO
voltages into correct ranges after the addition of
K160RX, and the addition of the RF/12V connectors for
the KPA100.  I wonder what might have changed to lower
the 10m output?

-Ben  K1NT

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[Leigh L. Klotz Jr WA5ZNU]

I had a problem with low output on the high bands that I traced to a
missing C150 (bottom board part) in the buffer amp before the XMIT
mixer.  Output was OK up to about the middle of 20m.

Your symptoms sound different, but what I found is that a loss in one
part of the distributed gain can be made up somewhere else with the ALC,
so you might check for missing components all along the transmit chain.

73,
Leigh/WA5ZNU

P.S. I just happened to have a spare C150 left over after I built my K2,
so I used that one to fix it.  Imagine that...
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