[Elecraft] K2/HF Packer Amp incompatability?

[Don Wilhelm]

  That sounds like the amp is not running linear.  First make sure the 
bias is set correctly.
Then do a test in CW mode -
Put a small amount of drive to the amp (measure it), and measure the 
output.  Compute the gain.
Increase the drive by a small amount, and again compute the gain.
Continue in small steps until you have reached the maximum output of the 
amp.
The gain should be the same if the amplifier is really linear.

If the input impedance of the amplifier is changing with drive level, 
that can be cured with an attenuator at the input - the driver will then 
see a more constant impedance.

73,
Don W3FPR


On 9/14/2010 9:57 AM, zendoc at netspace.net.au wrote:
> Hi Pat and group,
>
> FWIW,  I have just built an HF Packer Amp and have exactly the same problem with
> marked audio distortion on SSB when driving it with my FT 817nd. Maybe the
> problem isn't the K2?
>
> I have discovered others with the same problem, but no-one with a solution to
> this Amp's non-linear behaviour on SSB.  I was waiting to finish building my K2
> to try the amp with the K2, but I suspect now that the problem is with Amp.  I
> initially thought it was RF feedback and that the mic cord was the likely
> culprit.  But no amount of wrapping any of the connector cables through ferrite
> toroids has has any influence.  Audio is distorted on peaks in SSB and only when
> the Amp is on and running into an antenna.  Distortion is much less running the
> Amp into a dummy load and absent running the amp in bypass. Reducing the input
> power makes no difference to the audio quality.  I've tried running the Amp and
> the rig from separate power supplies and/or gel cells :  makes no discernable
> difference. I've never had any trouble with RF feedback before, running 600W
> from my AL 811 into the same antenna system.
>
> If you find any clues to a solution, please let me know.  Glad I bought the
> KPA100 for my K2!
>
> 73,
>
> John
> VK7JB
>
>
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