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

[Jack Berry]

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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