[Elecraft] KPA500 Hum

[Mike Fatchett W0MU]

Ok.  I just never heard it before.  I did recall others mentioning 
this.  It is not loud.  The amp works great.

J6/W0MU November 21 - December 1 2011 CQ WW DX CW
W0MU-1 CC Cluster w0mu.net


On 9/26/2011 1:07 PM, Eric Swartz - WA6HHQ, Elecraft wrote:
> Hi Mike,
>
> This doesn't sound unusual.
>
> There is also a normal amount of 'resting' idle low level transformer 
> hum, which varies with line voltage and frequency.  Also, when the 
> rear switch is on, the transformer primary is active even when the 
> front switch is off ( but the output windings are disconnected from 
> the amp.)  the front switch is more like a stand-by - active switch.
>
> 73, Eric   WA6HHQ
>
> ---
> www.elecraft.com
>
>
> On 9/26/2011 11:49 AM, Ron D'Eau Claire wrote:
>> What you are describing is very unusual, Mike.
>>
>> Typically, one will hear some hum from the transformer with  the "key 
>> down"
>> (full 500 watt carrier). It is most pronounced when using the green
>> transformer tap (lowest line voltage input). Normally there is no hum 
>> with
>> the KPA500 off, or when running the KPA500 at low duty-cycle loads 
>> such as
>> SSB, even at full peak power output.
>>
>> I'd drop a line to the elecraft support reflector and see what the
>> Ele-guru's say.
>>
>> 73,
>>
>> Ron AC7AC
>>
>> -----Original Message-----
>>
>> My KPA500 now seems to have the hummms.  It comes and goes whether the
>> unit is on or off.  It does go away when you turn off the rear switch.
>>
>> I noticed someone changed the tap and that appeared to fix the hum.
>>
>> I am running the amp on 110V.  My actual wall voltage is 119V.
>>
>> I did not notice this at all while I was at our Montana home over the
>> summer.
>>
>> Mike W0MU
>>