Posted by
Dave KD1NA on
Jun 18, 2012; 11:42am
URL: http://elecraft.85.s1.nabble.com/KPA-500-tp7557770.html
Everyone,
I have had my KPA500 linear for some time now and have been really happy
with it. I use it with my K3 and they communicate with each other via the
DB15 AUX cable that I built ( the one furnished by Elecraft was too short).
The only issue I have encountered is the finals in the linear seem to heat
up rather quickly causing the fan to kick in in a rather short period of
time. it doesn't matter if I use the dummy load or a good match antenna. I
also noticed the finals seem to cool rather quickly after the transmittion
is terminated and the fan turns on after about 30 seconds to one minute
after starting a ssb transmittion then goes to a higher speed after about
30 seconds more. If my transmittion time is greater then 2 to 3 minutes the
fans go to high and the final temperature is around 70 degrees C. I have
never had the linear go in to a fault because of heat.
The fix.
I removed the top, front, and right side panels of the KPA500. When I first
built the linear I realized the mounting screws that mount the Z panel to
the amplifier module were too long so I used the shorter ones that would
normally go to mount the top panel. On inspecting these screws they were
tight. Looking at the right panel I noticed there are 4 screws that mount
the panel directly to the amplifier's heat sink. They were not as tight as
I would have liked. I wanted to get the most efficient heat transfer from
the module so I carefully applied some heat sink compound to the side of
the heat sink of the amplifier module before carefully mounting the right
sied panel back on the amplifier. I carefully made sure the 4 screws that
mount from the panel to the heatsink ( which are normally covered by the
handle) were solidly and carefully tightened. After inspecting the
transformer connections and the rest of the inside of the linear I
reassembled it and tested it out.
Findings.
Now when I am running ssb typically the fan doesn't come on until well in
to the qso and never has the fan reach high mode. If I brick the key at 500
watts into a dummy load the fan goes high after about 2 minutes. I also
noted the finals heat up slower and cool slower and the left panel
temperature follows the final temperature..
Now the amp seems very happy and I am not bugged by the constant fan noise
during a qso.
I thought I would pass this on to everyone.
Thanks and 73
Dave KD1NA
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