KX1 - Low Power Output

[Oliver Olsen]

Hello,

 

I recently constructed a KX1 with the 30/80 meter option board, and I'm
having problems with low power out on all bands except 80 meters.  On a
13.8V power supply, I'm getting a hair over 3 watts, but only .5 - .7 watts
on 20 meters (measured on a 50 Ohm dummy load).

 

I checked the voltages on Q1, Q4, Q5 and Q6.  Interesting, on 80 meters, the
xmit voltages look OK, but on the other bands (e.g. 20 meters), the voltages
on Q4 and Q5 are lower than expected.  And just to make things interesting,
when I check the voltage on Q1 (gate or drain) during XMIT, output power on
20 meters jumps up to about 2 watts.  Actually touching the gate or drain
with any metallic object increases TX power on 20 meters.

 

I checked the current draw on 20 and 80 meters - current drain corresponds
with TX power output.

 

Any ideas?

 

Thanks in advance!  

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[Don Wilhelm-4]

First, check the soldering carefully.  If the solder connections look
convex (like a ball on the component lead), the connection did not
receive enough heat to flow the solder adequately onto the solder pad.  
If there is excess solder, wick it away and re-solder with a minimal
amount of solder and adequate heat (at least 700 deg F).  Watch the
solder flow - if it flows out to a thin, almost invisible, edge on both
the solder pad and the component lead, that is a good connection.  The
solder should be a bit concave - if it looks convex, it either has too
much solder or did not receive enough heat or both.

Check the low pass filter toroids (and T1 and L3 too) to be certain the
leads have been well stripped and tinned - if the solder connection
looks like a miniature volcano, you have a bad connection and the only
cure is to remove the toroid, re-tin the leads and re-solder it - you
cannot do a proper job of it while mounted on the board (I have tried
many times).

These two problems are the root cause for more than half of the repairs
I do.  It is seldom that I have to replace a part because it failed.

If you have questions about how a good solder connection should look,
check the drawings in the soldering tutorial on the Elecraft website
(and now being shipped with many of the kits).

73,
Don W3FPR

Oliver Olsen wrote:

> Hello,
>
>  
>
> I recently constructed a KX1 with the 30/80 meter option board, and I'm
> having problems with low power out on all bands except 80 meters.  On a
> 13.8V power supply, I'm getting a hair over 3 watts, but only .5 - .7 watts
> on 20 meters (measured on a 50 Ohm dummy load).
>
>  

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