KX3 Heatsink discussion

[hhoyt]

Sorry of this appears twice, I got a bounce on the first submission:

The Pro Audio Engineering Kx32 Heatsink has more surface area than any
other commercially available KX3 heatsink.  Regarding mass, more is not
necessarily better.  If you take two heatsinks with the same surface
area, on the initial key-down the one with more mass gives a longer
initial warmup time.  Unfortunately it also retains heat longer, meaning
on the subsequent transmit cycles, it still retains heat from the
previous cycle.  We strove to minimize the mass of our heatsinks, the
limitation ended up being rigidity and resistance of the fins to damage.

The limitation on convective heatsink efficiency is not the thermal
conductivity of aluminum, it is surface area.  Our tests show very
little thermal Δ (delta if your browser is ASCII only!) across the area
of any given heatsink of almost any convective design.  This is because
the limitation is dissipation due to convection.  If you model the
thermal path as a series string of resistances, the aluminum is very low
resistance and the surface to air resistance is very high.

For more information visit our website!

Cheers & 73,

Howie
Pro Audio Engineering

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[Jan-10]

OH ~ I think we all understand that the word "heat-sink" implies that it
might/will get warm :-)

BUT ~ I  originally asked about the "heating" of the KX3 when driving
the KXPA100 at 20W

SO ~ I experimented this morning with adjusting the power OUT of the KX3
while driving the KXPA100 amplifier.  With rotation of the Power knob on
the KX3, it climbs to 10W [as measured at the Output of the KX3] and
with further rotation of the knob, it drops to less than 2W  for ~ 40W
out from the Amplifier and about 4W yields ~ 100W from the Amp.

THUS ~ why should the KX3 heat-up when driving an amplifier ????

Cheers, Jan K1ND


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[hhoyt]

Hi Jan,

Elecraft designed the KX twins to run with maximum efficiency, so up to
10 watts, it is the more efficient PA in the KX3 which supplies the
output power with the KXPA100 in bypass, and when more than 10 watts is
dialed in the KXPA100 is enabled, and the KX3 throttles back to make the
KXPA100 output whatever is desired.

Cheers & 73,

Howie - WA4PSC

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