HI current 30 meters

[Shamrock]

I bought a K2, sn 01489 on ebay. Had to replace the PA transistors and drivers and R50. Upgraded the firmware. Anyway, on 30 meters, at 5watts, it draws 1.56a. At 10 watts, 3.42a. Also a bit high, I think is 40 meters which at 10 watts draws 2.46a, and 15 meters at 10 watts, 2.30a. The rest of the bands range from 1.80a to 2.14a at 10 watts. This is into a dummy load. Any suggestions would be appreciated.

[Don Wilhelm-4]

  First, check the number of turns on toroids L18, L19 and L20 in the
low pass filter.  I suspect they are OK, or you would have problems on
20 meters as well, but check anyway.

If this is a QRP K2, check the number of turns on T4.  Normally the
green wire is connected to the PA transistor collectors and has 2 turns
while the white winding connects to the Low Pass Filter and has 3
turns.  If you find only 2 turns on the side that connects to the LPF,
then the prior owner had would it for "better efficiency at 5 watts" -
but that also means poorer efficiency at higher power settings, and if
the KSB2 is installed, that winding must be changed back to 3 turns to
operate in a linear fashion.

Then I need to ask exactly what you have, and how you are determining
the power output?  Specifically, do you have the KAT2 or KAT100
installed and do you have the KPA100.

If this is a basic K2 with no tuner installed, the load must be a good
50 ohm non-reactive dummy load to achieve a good indication of power
output during a TUNE operation.

If you have the KAT2, KPA100, or KAT100, you must calibrate the
wattmeter in those options before getting a good indication of power
output.  Let me know what you have and I should be able to help further.

73,
Don W3FPR

On 10/25/2010 8:22 PM, Shamrock wrote:
> I bought a K2, sn 01489 on ebay. Had to replace the PA transistors and
> drivers and R50. Upgraded the firmware. Anyway, on 30 meters, at 5watts, it
> draws 1.56a. At 10 watts, 3.42a. Also a bit high, I think is 40 meters which
> at 10 watts draws 2.46a, and 15 meters at 10 watts, 2.30a. The rest of the
> bands range from 1.80a to 2.14a at 10 watts. This is into a dummy load. Any
> suggestions would be appreciated.
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[Shamrock]

Sorry, Don, I don't have the hang of this forum yet. My K2 is a bare bones unit with the exception of the audio filter. I have a Diamond SX-200 power meter and an MFJ-280C dummy load. It could be that it is wired for max efficiency at 5 watts, but even at 5 watts, 30 meters stands out with respect to current drain. At 5W, 30 meters draws 1.56a. The next closest band is 20 meters, 5 watts, 1.36a, and the lowest current drain is on 12 meters at 1.24a. I'll check those items you suggested and let you know how it goes.
Thanks
Jim
KG4TUM

[Don Wilhelm-4]

  Jim,

I am not sure about "the hang of this forum" thing.  It is just public
email where we try to help each other with Elecraft products.

You may have a problem with that wattmeter rather than the K2.  Analog
metered wattmeters are notoriously inaccurate, especially at low power
readings.  What range are you using on the wattmeter?  The thing about
these analog wattmeters (including the much revered Bird) is that they
have their accuracy specified as a percentage of the full scale
reading.  That means if you are using a 100 watt scale and the specified
accuracy is 10%, the reading can be off by as much as 10 watts - and
that is true *anywhere* on the scale.  Also, wattmeters can be frequency
dependent.

A normal K2 has more gain at 40 and 30 meters than on the other bands.  
Given the way the K2 controls power, you should have less current drawn
for any given power output on those bands.  If that is not true, then
the most likely place to look for the problem is in the Low Pass Filter
for the bands drawing excessive current, or the winding of T4.  Also be
sure Z1 and Z2 are in place and properly soldered.  You might want to
check the actual construction against the manual sections that detail
the winding of T4 and its installation.  If you do not have the manual,
you may download it from www.elecraft.com.

73,
Don W3FPR


On 10/25/2010 11:25 PM, Shamrock wrote:

> Sorry, Don, I don't have the hang of this forum yet. My K2 is a bare bones
> unit with the exception of the audio filter. I have a Diamond SX-200 power
> meter and an MFJ-280C dummy load. It could be that it is wired for max
> efficiency at 5 watts, but even at 5 watts, 30 meters stands out with
> respect to current drain. At 5W, 30 meters draws 1.56a. The next closest
> band is 20 meters, 5 watts, 1.36a, and the lowest current drain is on 12
> meters at 1.24a. I'll check those items you suggested and let you know how
> it goes.
> Thanks
> Jim
> KG4TUM

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[Shamrock]

Thanks for your insights. I'll take a look at all of what you have suggested. I use the 20 watt scale, the next lower scale is 5 watts. The K2 and the wattmeter agree on 10 watts on 30 meters, it's just the amount of current that bothers me. I appreciate your help.
Thanks
Jim