Hello all, I'm a new KPA500 owner as of last week and new to Elecraft other than a KX1 I had some years ago. The following may have been covered here before but I didn't see it in the archives. When choosing the proper power transformer tap I followed the instructions in the manual: I measured my 240V line and determined from the table in the manual that the yellow tap was the best, so that's what I used. This resulted in a no-load drain voltage of around 73 volts. Last night I did two-tone TX IMD3 tests at 500w and while the results were acceptable I wondered if they could be better. Later I got to thinking that more HV might improve those numbers, so as an experiment I selected the red tap (next one down) on the power transformer and checked the HV. This time it was 81V with no load, still within the 65-85v range specified in the manual. But the third order TX IMD numbers improved across the board by an average of 2.5 dB over my first test. On the bands above 20m the improvement was over 3 dB. Nothing to sneeze at when dealing with TX third order IMD products. By the way, my KPA500 third order TX IMD performance exceeds -40 dB (IMD3 below PEP, ARRL method) on several bands as tested with my rig.
One nice thing about the low drive requirements of the KPA500 (25 to 35 watts) is that the driving rig (in my case anyway) is very clean, IMD-wise, at those low power levels. I mention this because the KPA500 manual sort of implies that there is one "right" tap, but in my case there were two that were acceptable and one that was best. Of course your mileage may vary. This is a very nice amplifier - well designed, and the PIN diode switching is fantastic. So far I haven't missed my Drake L7 at all. 73, Doug K4DSP ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
