When you remove the KPA500 top cover, the Z-bracket is the metal bracket running from the front to back panels dividing the inside into the power supply (with the big transformer) and RF sections.
The Z-bracket attaches to the front and back panels, the bottom cover and to the top. Make sure you got all the screws tight. Also, be sure you installed the transformer correctly, including the rubber disk between the transformer and the bottom cover and you have the bumpers in place where the transformer rests against edge. Be sure the Bellevue washer is installed right side up. That's the washer under the nut holding the transformer in place. As the text explained, it is very slightly conical and must be installed so the center hole of the washer is slightly higher than the edges. Put it on the desk and tap on the edges of the washer with a pencil. If it rocks a bit, it is upside. If it is right side up, it will sit still. Be sure it is installed right side up. Finally, tighten the nut on the Bellevue washer a bit more. If you have a torque wrench available, it should be set to 55 in/lbs but it is not real critical. As the text says, run the washer down onto the Bellevue washer, and then tighten one or two turns further. IF needed add a bit more to quiet it! My KPA500 hums under full load, but not loudly - about as loud as my Astron power supply under full load. If anything is "buzzing" it is certainly a loose fastener somewhere. 73, Ron AC7AC On Sun, Oct 23, 2016 at 5:46 PM, W1GO (Joe) <w...@icloud.com> wrote: > > Hi all, > > Finished assembly of KPA500 and a little surprised at the magnitude of > hum / buzz during CW (no real issue on SSB); I've read about it but was > surprised at just how pronounced it is. I could use the KPA500 as a code > oscillator for practice; no need to keep monitor turned on. I've read > most of the historical dialogue regarding methods to minimize "the > buzz": use yellow wire tap, keep wires from touching chassis, make > sure everything (including transformer) is good and tight, etc. all > those things are done with little positive impact. I'm running off well regulated 240 VAC. > > I just wonder if anyone has any other "secrets" they might share. My > code proficiency is not great, at this point, and having the KPA500 > groan in response to my keying is somewhat distracting; even with > headphones when monitor is turned up higher than usual. > > Best regards, > > Joe > W1GO > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net Please help support this email > list: http://www.qsl.net/donate.html Message delivered to > k...@arrl.net > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to r...@cobi.biz ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
