KPA500 hum; horrendous

[Macy monkeys]

I'm certainly having my troubles with this new KPA500. The level of hum is unacceptable.

The manual says it is normal to hear hum. With 20 w drive I'm getting 350 watts out but the hum is horrendous when I send CW. SSB not so bad. Is this level of hum normal during keydown? It's room filling!

John K7FD
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[Bob McGraw - K4TAX]

Zero hum from mine.  From other comments, be sure the power transformer
is correctly installed and secured.  It may have moved during
transportation if you purchased a factory built unit.

As to 20 watts drive and 350 watts out, what bands?    With 20 watts
drive from my K3S I see 450 to 550 watts out on all bands as seen on the
amp LED indication and on an external {Bird 43} meter.    The HV is 62
volts and the current is 11.5 amps into a dummy load.  Amp is operated
from a 240 source.

73

Bob, K4TAX


On 11/6/2018 10:47 PM, Macy monkeys wrote:

> I'm certainly having my troubles with this new KPA500. The level of hum is unacceptable.
>
> The manual says it is normal to hear hum. With 20 w drive I'm getting 350 watts out but the hum is horrendous when I send CW. SSB not so bad. Is this level of hum normal during keydown? It's room filling!
>
> John K7FD
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[Macy monkeys]

I suspect that may be the case, Bob. I will wait until I hear from tech support before I pop  open then amplifier for a look-see. It is factory built.

Regarding power output, I was incorrect. On 80 and 40 meters I am seeing similar outputs as you. I am on a 240 source, HV is 74 volts.

John K7FD

> On Nov 7, 2018, at 5:19 AM, Bob McGraw K4TAX <[hidden email]> wrote:
>
> Zero hum from mine.  From other comments, be sure the power transformer is correctly installed and secured.  It may have moved during transportation if you purchased a factory built unit.
>
> As to 20 watts drive and 350 watts out, what bands?    With 20 watts drive from my K3S I see 450 to 550 watts out on all bands as seen on the amp LED indication and on an external {Bird 43} meter.    The HV is 62 volts and the current is 11.5 amps into a dummy load.  Amp is operated from a 240 source.
>
> 73
>
> Bob, K4TAX
>
>
>> On 11/6/2018 10:47 PM, Macy monkeys wrote:
>> I'm certainly having my troubles with this new KPA500. The level of hum is unacceptable.
>>
>> The manual says it is normal to hear hum. With 20 w drive I'm getting 350 watts out but the hum is horrendous when I send CW. SSB not so bad. Is this level of hum normal during keydown? It's room filling!
>>
>> John K7FD
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

[ANDY DURBIN]

Hum level depends on PA current draw from the torroidal transformer.  What is your PA voltage key down?  What is the complex impedance of the antenna system as measured at the amplifier?


I reduced my KPA500 hum level from intolerable to acceptable by adjusting the transformer voltage tap and bringing the antenna system load close to 50 ohm resistive.


Andy, k3wyc
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]