[Elecraft] K2/100 RF Power Output Control (SSB)

[Don Wilhelm]

Gene,

You may have a simple problem - diodes D16 and D17 in the KPA100 
wattmeter may be damaged.
When that happens, the K2 microprocessor thinks there is no power being 
developed and increases the drive to the maximum.
To test for that condition, set the power control to 4 or 5 watts and 
measure the actual power output.  If it is 14 or 15 watts (maximum power 
from the base K2) then it is a sure bet that there is something wrong 
with the wattmeter in the KPA100, and the diodes are the most probable 
source.

If you have proper power control up to 12 watts, then several other 
problems might be present.  If that is the case ask again and we can 
advise you where to check next - but do the diode checks first.  You can 
check them like any diode with an ohmmeter.

If the diodes are bad, you will have to remove the KPA100 and take off 
its shield plate.  There is a chance that you can replace the diodes 
(they are near the SO239 jack) from the top of the board, leaving short 
leads above the board to solder the new diodes - worst case, you will 
have to remove the board from the heat sink and unsolder the diodes from 
the bottom.

You may have heard advice to disconnect the K2 from the antenna when not 
in use, and you should heed that advice.  Those diodes can be damaged by 
static discharges coming in on the feedline.  Static can be caused by 
wind, rain, snow, lightning, etc. Plus, for your personal safety and the 
safety of those in your household, disconnecting the antennas is good 
insurance against fire or lightning induced shocks during a lightning storm.

73,
Don W3FPR

Eugene Balinski wrote:
> All,
>
>      Still new to the K2/100 (6k serial number). I have a
>  question about the power output control in SSB mode.  I
> was hoping to be able to vary the RF output from QRP all
> the way to the 100W level, however when I advance the RF
> Power knob past the 12W indicated on the display, I hear a
> relay click and the radio goes to the 100W+ output level.
>   This causes the power supply (RS-20) to actually go out
> of regulation (more than 22A) on voice peaks.
>
>     Is there an issue with the PO control, or does it
> behave differently with the 100W amp ?
>
>   73 and thanks in advance,
>
>