[Elecraft] Setting of FWD cal pot R26 in the KPA100

[Ron Willcocks]

Greetings
               Since making my KPA100 some time ago I always had the odd 
time when "HI CUR" would show, and I had tweaked the CAL CUR up to 
3.74amps, but when I started getting the over current message again after 
doing the latest PA mods and Firmware upgrade I decided it was time to find 
out what was going on.
I thought the best option was to call in the "Heavies" straight away, so I 
contacted Gary Surrency and received a prompt reply suggesting ( amongst 
other things) that R26, the FWD cal pot in the KPA100 might be set too low.
Apparently if this is so, it allows more than 100 -110watts output from the 
KPA100, which will demand more drive from the K2 and push the current 
required up..
I am not exactly flush with good test gear now-days so I borrowed a watt 
meter, and I was somewhat surprised to see I was delivering the best part 
of 140w on 20m.
I tried the R26/R27 adjustment according to the manual, and it just didn't 
seem to work out, so I contacted Gary again.
This time he suggested the R26 pot should show about 41 - 43k ohms to 
ground, and the R27 pot should be set about 20% higher.
Mine was set to 36k, so I adjusted it to 42K (as a starting point) and 
tried the output again. This time I was putting out around 110watts on 20m 
and drawing only 3.2amps. Tests on all the other bands showed decent output 
with reduced current readings, so I have left R26 where it is and put the 
set back together.
Why I had the trouble setting R26 in the first place is a mystery. I have 
made another K2/100 for a friend since I built my KPA100 and had no 
problems with that alignment.
Anyway, I record this saga here in case someone else has been caught out 
the same way? I imagine I made mine worse during the mods I did to the amp, 
by most likely bumping R26 a tad lower.
I have Cal Cur set to 3.50amps now.......Where would we be without Gary?
Cheers.......Ron ZL1TW