[Elecraft] Strange KPA100 behavior

[Don Wilhelm]

Mike,

If you are certain you had the red toroid cores (not any blue ones) then 
you have the older KPA100 T/R switch design - it must have been shipped 
before mid-Nov 2006.  You do not have to check C31 with the red toroid 
KPA100.

Do check to see if the KPA100 is displaying low power - you can do that 
check at low power by powering the base K2 and removing the power from 
the KPA100.  If the internal wattmeter is working, you will be able to 
control power output and have a correct power reading if the wattmeter 
is correctly calibrated.  If you cannot control power output, then you 
have something wrong with the wattmeter - T4 is the first suspect, check 
the lead placement and check the lead tinning carefully.  Be certain the 
red wire goes through the toroid core center and that the bare wire you 
soldered onto the SO239 jack is well soldered to the board at T4-6.

As for the 7:1 SWR you read on the Elecraft W1 - do investigate that, 
and I strongly suggest that the cause can be found in either your dummy 
load or in the connecting cables - use a very short coax connection to a 
dummy load.

73,
Don W3FPR

geddes at tampabay.rr.com wrote:
> Don,
> 
> I am not at home right now to look at K2, but will try and answer your 
> questions to provide additional information.
> 
> I am not sure what the K2 was displaying in terms of watts out (I 
> think it was a low number), but I confirmed the output at 165w using 
> two external wattmeters (first the Elecraft W1, which I did not 
> totally believe because it was maxed out, then my Bird 43 with 1000w 
> slug).  I was connected to a Bird 125w dummy load, confirmed 50 ohm. 
> The cable was probably not the best, it was a 20 ft run of RG-58 I 
> think.
> 
> My kit used the red toroids, and I assume at L15 and L16 but would 
> have to check when I can look at the kit (when I get home). Also will 
> have to check the value of C31.  
> 
> Don't know if this will help you or not . . but this is what I can 
> provide for now.  Will check the rest when I get home this evening.
> 
> Thanks,
> 
> Mike
> N4JX
>