[Elecraft] Which PS for K2/100, linear or switcher?

[Ron D'Eau Claire]

Vic wrote:
One other thing to keep in mind is that a slightly reactive load -- even 
with a reasonable SWR -- may change the current draw significantly.  I 
think this was my issue, actually.  Some band on which the antenna's SWR 
was about 1.4:1 nevertheless drew much more current than the dummy load.

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Absolutely! That's why I suggested that for anyone with a "chronic"
over-current problem it might be a problem with an output LPF network since
it can cause exactly that symptom even when feeding a 50 ohm non-reactive
load. 

Of course the Astron 20A can deliver considerably more than 20A on peaks
without trouble, but that should NEVER happen in normal operation since
tune-up should always be done at greatly-reduced power (typically 20 watts
or so). So the only real issue should be that of running full power into a
somewhat reactive load. 

You raised an interesting question so I tried a little experiment with
reactive loads on my K2/100. On 80 meters where mine draws 16 Amps at just
100 watts into an SWR of 1.0:1, the current demand increases to 18 Amps when
the SWR is increased to 2.0:1 with excess inductive reactance and actually
drops to 15 A when the SWR is increased to 2.0:1 with excess capacitive
reactance in the load (I have a center fed doublet with a manual balanced
ATU so it's easy to tinker with the SWR). If yours is hitting 20 amps, that
would be less than a 10% difference. I'd not be surprised to see that sort
of variation in rigs. 

My point was only that a 35 amp supply for the K2/100 was "overkill" and
that the 20A supply Elecraft recommends is plenty to supply a K2/100 with
full transmit current at 100 watts. I've never had the 20 amp "fast blow"
fuse in my power supply line open under any operating conditions. 

Some rigs may demand closer to 20 Amps than others, but there should not be
enough difference to be of concern or to justify using a bigger supply for
that reason alone. One point to keep in mind is that Astron rates their
supplies conservatively. Not all manufacturers are as careful as Elecraft
and Astron with their ratings. 

I've seen some posts here on the reflector saying that since Astron rates
the 20A supply at 16 Amps continuous duty it is being pushed hard by the
K2/100 which might draw closer to 20 Amps at times. That's simply not
correct. The 20A ICS rating that Astron gives for the supply is precisely
for the sort of load the K2/100 imposes on it at full power in normal
Amateur service. Even if someone was going to run their K2/100 key-down 24/7
as a beacon or something, they'd have to reduce the RF power significantly
below 100 watts to avoid damaging the K2/100. That would greatly reduce the
current demand on the power supply. 

Ron AC7AC