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

[Cameron Francey]

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