[Elecraft] KPA500 code oscillator

[W1GO (Joe)]

Thanks, Ron.  Did all suggested and ensured every screw and bolt tightened.  Reseated transformer and really tightened down.  Unfortunately, same hum on CW; even with less than 10W drive.

Back to the drawing board.

Thank you,

Joe
W1GO

> On Oct 23, 2016, at 5:56 PM, Ron D'Eau Claire <ron at cobi.biz> wrote:
> 
> 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
>