[Elecraft] [K2] Low power output

[Don Wilhelm]

Petr,

The specification for the K2 is for 10 watts or greater.  Most will go 
to 12 watts on 40 and 30 meters with an adequate power supply voltage 
while few can achieve 15 watts on all bands.

There is nothing specific to the KPA100 option that would cause low 
power output from the base K2.
However, there are a few things to check.

First check the value of R98 on the bottom of the board.  The normal 
value is 270 ohms, but after the addition of the KPA100, some 
experienced power oscillation due to the added RF Gain, and that value 
may have been increased to damp the oscillation.

Then check to make certain T4 was not wound for "greater efficiency at 5 
watts" with a 2:2:1:1 ratio instead of the normal 2:3:1:1 ratio - count 
the number of white turns on T4.  That 'more efficient' T4 is actually 
less efficient above 5 watts and should never be used with the KSB2 
option or the KPA100.

If there is also HiCur as well as low power then the problem is either 
with T4 or the Low Pass Filter.

Make certain the power supply leads are tight and large enough to keep 
the voltage drop low - a power source with at least 13.8 volts should be 
used and the voltage should not drop below 12.5 during transmit.  15 
watts is not possible with a lower voltage, and the output on 12 and 10 
meters may be less.  10 watts or more meets specification.

If those checks do not provide the answer, then he will have to do the 
"Transmit Signal Tracing" in Appendix A of the manual to identify the 
first stage with less than the expected RF voltage output.

73,
Don W3FPR

On 9/4/2019 6:47 AM, Petr, OK1RP/M0SIS wrote:
> Hi folks,
> 
> my colleque got as birthday gift from family the K2. All seems ok, receiver
> works excellent.
> The only issue he found is the low power output thru all bands. He can not
> get 15W but something
> below 10W... He mentioned in last email that preview owner had installed
> KPA100 option which
> has been removed probably before selling.
> Is there something related to KPA100 which could be modified and need to be
> now set back to get
> 15W from his K2 please?
>