[Elecraft] KPA500 Buzz SOLVED

[eric norris]

My KPA500 #274 worked fine with the yellow wire installed, but the voltage was a bit low (56-year old house) and output on 6M was also a tad low.  I wired it for 220v.  Since I use it for meteor scatter on 6m, I really wanted full output.  But when I switched to the red wire, I got a terrible buzz.  I don't mean a slight buzz, I mean a buzz on the order of an arc welder running at full tilt.  A buzz that was louder than when the pole pig across the street caught fire.  A buzz far too loud to be tolerated in a nice, quiet, Elecraft-equipped shack.  
 
I tried repositioning the transformer a number of times to no avail.  I finally contacted Gary at Elecraft support, and working with him got the problem solved.  Here's what I did:
 
1)  Replaced the transformer hold-down bolt that was threaded only at the top with a bolt that was threaded all the way down.  I installed this according to the new procedure in the KPA500 assembly manual (this is now shipped with all KPA500s).  
 
2)  I zip-tied together a number of the wires so that they were not contacting the transformer or the top of the case any more than was necessary.
 
3)  I used a torque wrench to install the transformer to the correct spec in the manual.
 
I'm not sure what fixed it, but the buzz is now down to a very slight, almost unnoticeable level.  I have silent QRO on CW.  Luxury.    
 
I offer this for anyone with an early KPA500 with a loud buzzing problem.  When this thread was active there seemed to be some confusion about what was a normal buzzing level.  Wayne stated that some buzz was normal, but I am sure that others experienced this extremely loud buzz that is not normal.  I never saw a resolution of this thread, so if I missed it my apologies.
 
73,
 
Eric WD6DBM