[Elecraft] K2/100

[W3FPR]

Andrew,

With the KPA100 installed, and the power set to 10 or 11 watts, what is 
the actual power output in TUNE?
It should be near 2 watts.

If not, there is a problem in the VRFDET section of the KPA100 or in the 
base K2.
First, remove the KPA100 (physically) and try it with just the base K2.

If the base K2 is OK, then yoou have some KPA100 problem to solve.  Put 
the KPA100 upside down on a box or book about 1/2 the height of the K2 
and remove the shield.

set the power to about 50 watts and prepare to do some voltage measurements.
Measure the voltage at U5 pin 5 - then at 5 pin 7, they should be close 
to the same voltage.
U6 pin 3 should be about 1/2 that voltage.  If not, the problem is Q10 
and possibly Q11.

If all OK this far, then make certain U6 pin 8 is near 5 volts.
If so, then check U6 pin 6 and tell me what the voltage there actually 
is.  U6 is a common failure.

73,
Don W3FPR

On 7/26/2026 1:16 PM, Andrew Lenton via Elecraft wrote:
> Hi I have just performed all the mods on the KPA100 and reset the FWD 
> and REF and set the bias at 400mA, my bird watt meter tracks the 
> indicated power on the K2
>   After fitting the screen and putting it all back together it works 
> fine on SSB.
>   On low power tune is fine, however on more than 11 Watts pressing 
> tune causes the power to jump to 140 and the SWR 2.2:1, so suspecting 
> it is "hooting" when all back together.
>
>  Before I dive in an suggestions?