Humming KPA500

[Edward A. Dauer]

KPA500 started a new routine today after several years of perfect operation.  It emits an audible hum at a frequency of 60 Hz with a rise and fall time of 3 to 4 seconds.  It’s just loud enough to be annoying.  It continues whether the front panel power switch is on or off.  It ceases only when the rear panel power switch is off.  Neither the temperature of the amp nor the duty cycle have any no bearing on it, as the noise persists even when the amp comes on from dead cold.  Anyone heard this in a KPA500, or have any ideas about it?  Is something expensive about to happen?

Ted, KN1CBR

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[Clay Autery-2]

Loose PS transformer?

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Clay Autery, KY5G

On 9/2/2017 9:40 AM, Dauer, Edward wrote:
> KPA500 started a new routine today after several years of perfect operation.  It emits an audible hum at a frequency of 60 Hz with a rise and fall time of 3 to 4 seconds.  It’s just loud enough to be annoying.  It continues whether the front panel power switch is on or off.  It ceases only when the rear panel power switch is off.  Neither the temperature of the amp nor the duty cycle have any no bearing on it, as the noise persists even when the amp comes on from dead cold.  Anyone heard this in a KPA500, or have any ideas about it?  Is something expensive about to happen?
>
> Ted, KN1CBR

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[Elecraft mailing list]

Mine does the same thing.  I opened it up last year and could not find
anything loose.  Would like to get it resolved.  

Tex ka5y



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[Deni F5VJC]

Switching or variation of load on your AC supply?

On 3 September 2017 at 00:43, pkhjr via Elecraft <[hidden email]>
wrote:

> Mine does the same thing.  I opened it up last year and could not find
> anything loose.  Would like to get it resolved.
>
> Tex ka5y
>
>
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
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[Richard Lamont]

On 02/09/17 15:52, Clay Autery wrote:

> Loose PS transformer?

The assembly manual for the kit suggests that, although it isn't
necessary, if you have a torque wrench you should tighten it to 55
inch-pounds.


73,
Richard G4DYA
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