Dear Folks:
I have been using my KPA-500 (driven by the K3s and transmitting through
the KAT-500) for about five years now. I have long noticed that, when
first using it, or if it has sat idling for a while, the amp's supply
voltage will be low on transmit and won't go higher until the amp has
been used for a couple of minutes. This becomes critical in some
instances since, particularly on 20 meters, the supply voltage will be
below 60 volts on transmit for a while and won't increase unless I
reduce the drive power by a few watts. I do always reduce the drive
power to make sure the supply voltage stays at 60 or above (I have been
told that this keeps the amp operating within normal limits and the math
indicates that this will make sure the current doesn't get too high).
Once I've been transmitting for a minute or two (I almost always use
CW), the amp appears to warm up and I can bump up the drive power a few
watts for higher power output and still keep the supply voltage at 60 or
above.
For the record, the amp is plugged into a normal wall outlet supplying
117VAC (or whatever the house is supplying at that moment), though it is
not using any of the same outlets that the rest of the shack uses. I
realize it is highly likely that all the outlets in the shack are on the
same breaker, but my prior tube-type amp used to dim the lights a bit
when I keyed it and had it plugged into the same outlets as the rest of
the shack. That stopped happening once I switched the outlet for the
tube amp and now I'm using that same outlet solely for the KPA-500.
My first question is whether any of you with a KPA-500 experience the
same thing, i.e., supply voltage is a little low at the beginning and
increases as the amp warms up?
My second question concerns the fact that, even with the amp warmed up,
I can seldom (if ever) hit 500 watts out on 20 meters, though I can do
it easily on all the other bands (I recognize that this is likely caused
by my antenna's characteristics on that band, though SWR doesn't exceed
1.7 at any frequency that I use, even without the tuner). I simply
can't get the drive up high enough to get there, without the supply
voltage dipping below 60. Usually, I can get between 350 to 425 watts
out. Do you think this would be different if I had a 220 volt outlet
installed in the shack? For the record, I recognize that the 100 watt
or so decrease in power out doesn't make that much difference. I am
asking because I wonder if it would be easier on the amp to run it off
of a 220 volt outlet.
As always, thanks for any help and advice.
73 de Bernie, KF0QS
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