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.
-------------- 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 _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
