[Elecraft] Elecraft K2/10 Build and a lesson learned.

[Vic Rosenthal 4X6GP]

Many moons ago when there was a K2 but no KPA100 I wanted to drive an 
amp with my K2 and I needed a few more watts. I made some modification 
(I don't remember the details) that allowed it to produce more than 20 
watts, which made a big difference in output from my amp. I operated for 
a while like that until the KPA100 came out, and it didn't seem to hurt 
anything.

73,
Vic, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/

On 26 Feb 2017 01:02, Cameron Francey wrote:
> Hi All,
>
> I Just finished my Elecraft K2/10 build.  I have lots of options to
> add but the basic K2/10 is now working and I'll let it settle in for
> a week or so to make sure its all ok before adding any options.
>
>
> I started this build at the end of January, taking care to sort and
> identify all the parts, especially the fixed value capacitors so it
> made life much easier to select the correct values efficiently during
> the build.
>
> Everything went well, got the phase 1 and 2 tests done, added the
> remainder of the components to finish phase 3 and then when I got to
> the transmitter alignment step I noticed that rather than about 2
> watts out as expected it was over 20 watts!  Gee, what was wrong I
> thought to myself?  I had a quick look over everything, made 100%
> sure all the components were installed correctly etc, but couldn't
> find anything wrong.  I even re-counted all the transformer winding's
> and made sure they were all installed correctly.  Nothing looked out
> of place.
>
>
> Having recently built two K1's and a K2/100 with KAT100 and nearly
> every option available I knew it had to be something I had done
> wrong.  So I kept my logic head on and decided after my initial
> disappointment and re-checking my work that a break away from the
> bench was a good start.
>
>
> Back to the bench this morning with a fresh mind I suspected that my
> issue was somehow with the components that either set or control the
> power level,  and my reason for thinking that was because the issue
> was present on every band and the power control pot made no
> difference to the output power, and RX wise it was performing really
> well so that eliminated a lot of the sections.  Thinking about ALC or
> the power control circuit on the control board I decided that was
> where to start and work outwards from there.  I knew the transmit
> section of the main RF board was in good shape since it was capable
> of producing more than 20 watts into a dummy load!
>
>
> So, I read the circuit diagram, pulled out the control board and
> started to trace the ALC circuit though the board.. That's when I
> found my problem, I couldn't believe how stupid I had been and missed
> soldering pin 2 of RP 3 on the Control Board, which is the ALC
> feedback loop.  After soldering that and re-testing all was well,
> phew!!!
>
>
> Where the lesson was learned was even though I'm close to obsessive
> compulsive when identifying and selecting each component and double
> checking twice before soldering anything, then checking with a
> magnifying glass that the joints look good I still somehow managed to
> let that un-soldered pin go unnoticed!
>
>
> I don't think I have caused any adverse effects to the PA section
> driving it so hard.  The short periods of transmitting at about 23
> watts never caused them to heat up.  Its interesting that the PA
> produced over 20 watts, so the 15 watts max output under normal
> conditions seems quite a conservative level for those 2SC1969's.
>
>
> Just thought I'd share my stupid mistake with the readers here and
> that even being really careful things can still slip through the
> net!
>
>
>
> Best Regards,
>
> Cameron, AF7DK/GM7LQR