Posted by
Don Wilhelm-3 on
May 16, 2005; 2:24am
URL: http://elecraft.85.s1.nabble.com/K2-current-draw-tp378454p378456.html
Vic,
There are only 2 things that have potential for causing higer drive
requirements on 20 meters - the base K2 low pass filter and the base circuit
of the KPA100. I have not noticed any problem with 20 meters on all the
KPA100s that I have worked on (but I follow the manual recommendation to set
CAL CUR to 3.5 Amps, and I look no further), so I suggest that you look
carefully at the resistors and capacitors in the base circuit of the KPA100
and count the turns on the toroids for the 20/30 meter portion of the K2
LPF - my bet is that you can 'tweak' the windings in the K2 LPF to improve
the situation - one extra turn on a toroid (L18, L19 or L20) can lower the
frequency enough to reduce to power output per ampere (actually increse the
current draw) from the base K2 on 20 meters, and not be noticable under any
other conditions - the load presented by the KPA100 is not precisely 50 ohms
on all bands, hence my suggestion to investigate the base circuit. OTOH,
the KPA100 manual recommends that the CAL CUR be increased to 3.5 Amps when
the KPA1000 is installed, so things are still within expectations, but with
fine tuning, you may be able to do better than average.
73,
Don W3FPR
> -----Original Message-----
>
> I just noticed an interesting thing about my K2/100: the current
> drawn by the
> low-power part of the K2 (that's the current measured when you
> tap DISPLAY) is
> extra high on one band: 20 meters. When I'm running 100 watts
> out, the current
> displayed varies from about 2.2-2.8 amps on all bands other than
> 20. On 20,
> it's 3.5 amps.
>
> My first thought was that the bandpass filter was misaligned on 20. Sure
> enough, after adjusting L7 and L8 on 30 meters, the 20-meter
> trimmers were at
> minimum capacity when the output peaked. I had to add an 8 pf
> capacitor across
> one of them and a 27 pf capacitor (!) across the other in order
> to have the peak
> fall in the adjustment range of the trimmer. Very suspicious.
>
> After doing this, I verified that the current draw when running
> 10 watts on 20
> meters was in line with the other bands. But when running 100
> watts, I still
> get 3.5 amps!
>
> Something funny is going on. Why was I unable to get a peak on
> 20 without extra
> capacity across the bandpass filter trimmers? And why is the
> current drawn at
> 10 watts normal, but high at 100 watts?
>
> This is not something new, I've just ignored it until now!
>
>
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