[Elecraft] [QRO] KPA500 variation of PA current band-by-band

[Mike Harris]

Given that the poster is in the UK can probably assume 240Vac.

Regards,

Mike VP8NO

On 04/02/2012 17:31, Jack Berry wrote:
> 120 or 240 volts supply?
>
> On Feb 4, 2012, at 2:27 PM, david park<contrast014 at yahoo.com>  wrote:
>
>> I have recently assembled KPA500 serial number 641.  When testing into a dummy load I find that I get a large variation in the DC power input when driving for 500W CW when I go from band to band. My worst band is 21MHz, where I get the highest current (lowest efficiency).  The drive was adjusted to give 500W as indicated by the LCD display.  Here are my results:-
>>
>> 1.8MHz      DC current 10.0A    fan hardly ever comes on
>> 3.5MHz      DC current  10.0A   fan hardly ever comes on
>> 7MHz                             12.0A
>> 10.1MHz                        12.4A
>> 14MHz                           14.3A
>> 18.1MHz                        13.8A
>> 21MHz                           16.4A   temperature rises rapidly and fan soon gets to full speed
>> 24.9MHz                        13.5A
>> 29.7MHz                        12.3A
>>
>> I have no results for 50MHz band as I have no transceiver covering that band.
>>
>> The readings drift as the heatsink (and the dummy load) warm up, and so I took readings quickly and allowed time for the heatsink to cool down between each band. I find that the KPA500 current sensor tends to give low readings.
>> I would be interested in knowing how other amplifiers perform.
>>
>> David Park G3PSV
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