Thursday, January 3, 2013

PA checkout day

Provoked by an email by G4BVY after borrowing his 1kW 30dB Bird Tenulune I decided it was time to test out some amplifiers

First up was my Elecraft KPA500. It still had the old V1.11 software so this was upgraded to 2.23. It was then tested out and worked fine, a good tryout in preparation for this weekends ARRL RTTY contest

Next up was the 70MHz amplifier. Previously I had acquired a DEMI 48V 50MHz 300W PA. As the KPA500 gives me 500w on 6m it was decided to put it on 4m. Steve told me the only thing that would need changing is the low pass filter. Looking in the junkbox and finding some UNELCO caps and some 2mm silver plated wire one was built and installed.

Next a 48V power supply was needed. I had bought an Erskine one from Jim GI1CET on ebay (I first saw them when he had them at the EME2012 conference but was too late to get one) Unfortunately it produced 54V, bit high for the amplifier. Using the instructions provided,  the cover and sisterboard were removed and a 220k resistor put in parallel with the 22k resistor to the right of the voltage set pot. This gave me the 47-50V range which was ideal

Hooking up the PA to the output of the DEMI 70MHz xverter (configured so that whatever i did it could only run 10W maximum, rather than its normal 35W) 8W gave me 370W on 4m . A quick test showed that it still gave 400W  on 6m for 6W of drive, both of which were acceptable

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